| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Key Laboratory of Colloid and Interface Chemistry (Shandong University), Ministry of Education, School of Chemistry and Chemical Engineering, Shandong University, Jinan 250100, China
Correspondence: Address reprint requests to Jinghe Yang, Fax: 86-531-8564464; E-mail: yjh{at}sdu.edu.cn.
 |
ABSTRACT |
|---|
 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
|---|
|
INTRODUCTION |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
|---|
). The protein-surfactant interactions are important because they can shed light on the functional properties. Over the past decade, protein-surfactant complexes have been studied extensively in the field of chemistry, biochemistry, and food science. It is well known that surfactants bind strongly to protein, thereby inducing conformational changes in the protein. These conformational changes often result in changes of polarity and stability of the protein. Many methods have been used to investigate these changes, such as calorimetry for thermal stability (Kelley and McClements, 2003), turbidimetry for protein aggregation (Valstar et al., 2000), fluorometry for polarity (Ray and Chakrabarti, 2003), and NMR for structure of complex (McCoy and Wyss, 2002), etc. Different models to describe the saturated protein-SDS complex have been summarized by Guo (Guo and Chen, 1990) as follows: 1), the "rodlike particle model" (Reynolds and Tanford, 1970a,b); 2), the "flexible helix model" (Lundahl et al., 1986); 3), the "necklace model" (Shirahama et al., 1974); and 4), the "
-helix/random coil model" ((Mattice et al., 1976). Among them, the necklace model seems to be best supported by experimental results, obtained with techniques such as small-angle neutron scattering study (Ibel et al., 1990; Chen and Teixeira, 1986), viscometry (Shinagawa et al., 1993), and NMR (Turro and Lei, 1995), etc. It was reported that NMR could distinguish the two possible "necklace and bead" structures (Turro and Lei, 1995); in one the surfactant aggregate wraps around the hydrophobic parts of protein because of hydrophobic interactions, and in the other the protein wraps around the surfactant micelles. Recently, Gelamo and his co-workers (Gelamo et al., 2002) described the modeling of bovine serum albumin (BSA) with low concentration of anionic surfactant (SDS) and cationic surfactants (CTAC and HPS), which was monitored by fluorescence spectroscopy of the intrinsic tryptophan residues.
However, the surfactants used are typically anionic surfactants such as SDS because it has a stronger interaction with the protein compared to cationic surfactants (Nozaki et al., 1974; Ananthapadmanabhan, 1993). In addition, the surfactants are usually controlled to be at the low concentrations. It is valuable for us to know the changes of BSA at the high concentration of surfactants. Herein, we investigated in deeper details the interaction of BSA with aromatic cationic surfactants CPB from low to high concentrations, mainly at the concentrations of its first and second critical micelle concentration (CMC). The study also proposed the structural models of protein-CPB complex and evaluated the effect of the aromatic ring stacking between BSA and CPB.
|
MATERIALS AND METHODS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
|---|
Methods
Ultraviolet-visible (UV-vis) spectroscopy was recorded on a Hitachi UV-4100 spectrophotometer at room temperature in a 1-cm quartz cuvette. Static fluorescence spectroscopy was recorded with a F4500 spectrofluorimeter (Hitachi, Tokyo, Japan) in a 1-cm quartz cuvette and the excitation and emission slits are both 5 nm with the scan speed of 1200 nm/min. Far-UV and near-UV circular dichroism (CD) spectroscopy was carried out on a JASCO J-725S spectropolarimeter (Easton, MD). The 1H-NMR spectroscopy was recorded with a Bruker (Billerica, MA) Avance-600 spectrometer (600 MHz) using D2O as solvent. Chemical shifts were reported in ppm (
) relative to internal standard tetramethylsilane at 0.00 ppm. CMC data were measured on a processor tensiometer-K12 (with a precision of 0.01 mN x m–1; Krüss, Hamburg, Germany) by the Wilhelmy plate. Small angle x-ray scattering (SAXS) curves were obtained at the SAXS beam line of a Philips PW3830 x-ray generator (Eindhoven, The Netherlands) (50 K, 40 mA), at room temperature (22 ± 1°C), with radiation wavelength 
= 1.542 Å and sample-to-detector distance of 233 nm with an MBRAUN (Stratham, NH) position sensitive detector. The obtained curves (data collection of 16 min) were corrected and normalized by taking into account the decrease of the x-ray beam intensity during the experiment. Due to the samples' attenuation, the parasitic background (buffer solution) was subtracted.
|
RESULTS AND DISCUSSIONS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
|---|
; Caspi and Ben-Jacob, 2000; Tao, 1981). The decrease was considered to be the result of the conformational changes due to the increase of the -helix content (Gaggelli et al., 2002; Tao, 1981). This surfactant-induced unfolding process could be illuminated by the curve of the absorbance variation 
A caused by the addition of CPB versus the logarithm of the concentration of surfactant (Fig. 1 b). Five characteristic regions were observed, indicating the binding of surfactant as a ligand to BSA. The curve in the left four regions (from 1 to 4) was in good agreement with the binding isotherms reported previously (Jones, 1975). The main unfolding process of the protein was believed to occur in the cooperative binding region 3 and the normal micelle formation occurred as excess surfactant was added in the region 4. Thus, it is believed that at the inflexion point between the 3 and 4 regions, the maximum unfolding occurs when CPB concentration is 1.00 x 10–5 mol/L, which is near the first CMC of CPB (1.50 (±0.01) x 10–5 mol/L) in the absence of protein as determined by the Wilhelmy-plate method. It is deduced that the unfolding is completed when CPB reaches its first CMC.
|
225 nm. The absorbance and the peak position moved toward shorter wavelengths with the increase of CPB concentration. And these changes were presented in region 5 of Fig. 1 b. Folding reoccurs for BSA, possibly meaning a renaturing process. However, in this region BSA differs from native BSA because this peak does not come back to 200 nm, indicating the changes in polarity of the microenvironment. In addition, the second CMC of CPB in the absence of BSA was obtained to be 8.50 (±0.13) x 10–5 mol/L with pyrene as a fluorescence probe according to the reported method (Li et al., 1985). So this alteration of secondary structure of BSA occurred near the second CMC of CPB.
Far-UV CD spectroscopy gave quantitative information on the secondary structure mentioned above (Fig. 2 a). The spectra (normalized to residue molar ellipticity) were analyzed with the software DICROPROT by self-consistent method to get structural information from the spectral changes (Deleage, 1993). At the first CMC, the CD spectra gave a large value of molar ellipticity at 222 and 208 nm, indicating an augmentation of the -helix content in BSA structure from 49 to 78%; at the same time, the ß-sheet content decreased from 9.8 to 7.6%. When CPB concentration reached the second CMC, the molar ellipticity decreased, yielding a broad minimum at 217 nm, where -helix was calculated to be 37% and ß-sheet to be 10.5%.
|
; Kelly and Price, 1997; Price, 2000), were recorded at different CPB concentrations, and the results were shown in Fig. 2 b. It was shown that there were two minima at 261 and 268 nm as well as two shoulders at 277 and 284 nm. An increase in the ellipticity at 261 and 268 nm and a decrease from 280 to 300 nm at the first CMC of CPB denote a change of tertiary structure, especially the loss in asymmetry around disulfide bridges and the changes in the environment of the tryptophan residue. Under this condition, BSA is less compact compared to the native state. When CPB concentration reached its second CMC, there was a slight loss in the CD signals at 261 and 268 nm compared with those of native BSA, reflecting the perturbations that existed around numerous disulfide bridges, which resulted in the revivification of tertiary structure. Apparently, this revivification is not the same as that of native BSA based on their different near-UV CD spectra. In addition, a small raise in ellipticity in the region between 280 and 300 nm was observed, which was ascribed to the changes in the environment of the tryptophan residues. Based on the results mentioned above, we suggest that at low CPB concentration, the surfactant molecules bind on the surface of protein through electrostatic and hydrophobic interactions, causing the protein to expand somewhat. Large amounts of CPB molecules are adsorbed on the surface of the protein with the increasing concentrations of CPB, resulting in the formation of the aggregates (such as micelle-like clusters). The intrachain hydrophobic interaction is replaced by the repulsive force, leading to the expanding of polypeptide and the unfolding of BSA, and finally destroys the tertiary structure.
When CPB concentration reaches its second CMC in BSA-CPB system, the surfactant molecules aggregate in the big rod micelles with strong hydrophobic inner core, resulting in stronger hydrophobic interaction between CPB and BSA in comparison to their electrostatic force. In addition, the dimension of rod micelle is similar to that of BSA (May and Ben-Shaul, 2001). Far-UV and near-UV CD studies also indicate that the secondary and tertiary structures of BSA under this condition were compressed and refolded. On the basis of above reasons, we propose a structural model of CPB-BSA complex at the second CMC of CPB in which BSA molecule penetrates into the rod micelle of CPB. In this packing model, the rod micelle limits the expanding of BSA molecule. On the other hand, the stronger hydrophobic interaction makes the hydrophobic part of the BSA molecule expose outside while its hydrophilic part is totally buried inside. Thus, BSA is refolded again, but the refolding is different from that in the aqueous environment, and refolded structure is different from the native BSA according to their far-UV and near-UV CD spectra.
1H-NMR studies
Here, we chose the NMR method to obtain the information on the mobility of different parts of surfactant molecule, e.g., headgroup region versus tails, and in turn, provided the information on the location of the protein in relation to the surfactant headgroups and the tails in the complex. In this article NMR spectra of 1.0 x 10–5 and 9.0 x 10–5 mol/L CPB and their complexes with 1.0 x 10–4 g/mL BSA were shown in Fig. 3. Corresponding to the pyridine in the headgroup of CPB, there were three clusters signals (Sun et al., 2004); the peaks at the chemical shift of 9.169, 8.774, and 8.298 ppm in Fig. 3 (1) corresponded to the H-2, H-1, and H-3, respectively. When CPB was mixed with BSA near the first CMC, three signals were broadened and moved to upfield significantly. The broadening effect indicates a significant reduction in the headgroup mobility and the involvement of the headgroup in the protein-surfactant aggregate, which supports the model that the protein wraps around the micelles or premicelles.
|
) between the pyridine in CPB and the residues (such as tryptophan, tyrosine, or phenylalanine) in BSA. Governed by the position of the protons relative to the ring, the magnitude of the chemical shift may serve as a measure of the extent of stacking. The strength of aromatic ring stacking in solution may be evaluated by stacking efficiency 
(Ladokhin et al., 1999), which can be calculated from Eq. 1:
 | (1) |
and 
are observed upfield shift value and the shift expected for complete stacking, respectively. And can be estimated according to a simple model of aromatic ring stacking:
 | (2) |
The association constant K is defined by:
 | (3) |
can be calculated by 
usingEq. 4:
 | (4) |
and 
represent the shift in monomeric A and in a complete stacking, respectively.
In our system, K in Eq. 3 was calculated by fluorophotometry (Guo et al., 2003) according to Eq. 5:
 | (5) |
|
for H-2 and H-3 are 0.179 and 0.085, and the corresponding efficiency are 0.76 and 0.73, respectively. This indicates that these two protons are the closest to the aromatic rings of BSA. When CPB reached its second CMC, these signals become as narrow as those of the pure CPB except a little upfield moving, indicating that the headgroups of CPB gain their mobility again due to the departure from the BSA surface. This result is considered as the form of rod micelles at CPB's second CMC. And the upfield moving in the spectra is considered to be the result of the weak aromatic rings stacking between the CPB molecules themselves.
Fluorescence spectroscopy
Fluorescence measurements showed that the addition of CPB could markedly influence the fluorescence of BSA. At the excitation wavelength of 290 nm, BSA was excited and the emission peak was at 350 nm. When a low concentration of CPB was added, the BSA emission was enhanced (Fig. 4 a). This enhancing effect reached a maximum at 1.25 x 10–5 mol/L CPB and remained constant until 7.50 x 10–5 mol/L, then the fluorescence of BSA was quenched suddenly, as shown in Fig. 4 b. The second-order derivative fluorescence spectra were recorded to analyze the details of this enhancement, which were shown in Fig. 4 c. The peak at 280 nm was attributed to tyrosine residue and the peak at 320 nm was attributed to tryptophan residue (Wang et al., 2000). In the presence of CPB, the peak of tryptophan residue increases significantly, indicating that it is the main contributor for the BSA fluorescence. The I– quenching test proved that the dosage of I– required to quench the fluorescence of unfolded BSA in the first CMC of CPB was about twice that required for native BSA. There are two tryptophan residues in one BSA molecule: Trp-134 in the eighth helix of D129-R144 in domain I, and Trp-213 in the second helix of E206-F221 in domain II (McLachlan and Walker, 1977). Only the helix of Trp-134 is active to interact with ligand in native BSA (similar to known crystallographic structure of human serum albumin (PDB1BJ5)) (shown in Fig. 5). As a ligand, CPB with low concentration primarily acts on Trp-134 through the aromatic ring stacking, which was proved by our NMR measurement above. With the increase of CPB concentration, Trp-213 gradually is exposed to the surface of BSA and interacts with CPB due to the unfolding of BSA. When CPB reaches its second CMC and above, BSA is refolded and tryptophan residues are hidden from CPB, and accordingly the aromatic ring stacking between CPB and the tryptophan residues disappears.
|
|
):
 | (6) |
the scattering vector; 2
, the scattering angle). In this study, the concentrations of both of BSA and CPB were low enough that they could be considered as a widely separated system (not interaction system, S(q) 
1). Hence, I(q) can be represented as (Improta et al., 1998):
 | (7) |
The inverse Fourier transform of I(q) yields P(r), which is the frequency of vectors connecting small-volume elements within the entire volume of the scattering particles (Glatter and Krathy, 1982):
 | (8) |
The behavior of P(r) provides the information about the shape of the scattering particles, thus it is extremely sensitive to the disposition of domains within a multidomain structure, and it goes to zero at the maximum linear dimension Dmax of the molecule. Moreover, the particle radius of gyration Rg is derived from P(r) and gives a simple measure of the distribution of volume elements within the molecule away from its center-of-mass, which is defined as the root-mean square of all elemental volumes from the center-of-mass of the particle, weighted by their scattering densities. 
can be represented as (Glatter and Krathy, 1982):
 | (9) |
The SAXS experimental results are presented in Fig. 6. It can be seen that there are obvious difference between the curves of BSA in the absence and presence of CPB at both the first CMC and above the second CMC. Compared to the native BSA, two distinct regions in the SAXS curve are marked when CPB is added. One has a greater slope than that of native BSA in the small q region, suggesting an increase in the scattering particle size, and another one has a different decay in the scattering curve, indicating changes of the protein shape. The data were analyzed through the distance distribution function p(r) using the GNOM program for Eqs. 8 and 9 (GNOM program is available free at ftp://ftp.embl-hamburg.de/szx.) When CPB is at its first CMC, calculated values of Rg and Dmax are 41.4 and 145 Å for BSA-CPB, and 30.2 and 95 Å for the native BSA, indicating a CPB-induced protein expanding. Whereas, when CPB concentration reaches its second CMC, Rg and Dmax decrease to 34.1 and 99 Å, which are a little bigger than that of native BSA but obviously smaller than those in BSA-CPB at its first CMC. Therefore, there is clear evidence that the expansion of BSA is limited and the size of the complex is decreased. In addition, it can also be seen from Fig. 6 that both Rg and the scattering intensity (I) have significant enhancement at the first CMC of CPB, which is considered to be the result of the aggregation between the clusters of BSA-CPB via the interaction between the hydrophobic patches exposed on the polypeptides chains in BSA. On the contrary, both Rg and I decrease at the second CMC of CPB, which indicates the decreasing of the aggregation mentioned above.
|
|
|
CONCLUSIONS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
|---|
|
ACKNOWLEDGEMENTS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
|---|
This work was supported by Natural Science Foundation of Shandong Province, and by Visiting Scholar Foundation of Key Laboratory at Shandong University.
Submitted on August 18, 2004; accepted for publication February 4, 2005.
|
REFERENCES |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
|---|
Caspi, S., and E. Ben-Jacob. 2000. Conformation changes and folding of proteins mediated by Davydov's solution. Phys. Lett. A. 272:124–129.[CrossRef]
Chen, S. H., and J. Teixeira. 1986. Structure and fractal dimension of protein-detergent complexes. Phys. Rev. Lett. 57:2583–2586.[CrossRef][Medline]
Clegg, R. M. 1995. Fluorescence resonance energy transfer. Curr. Opin. Biotechnol. 6:103–110.[CrossRef][Medline]
Dalgleish, D. G. 1996. Food emulsions. In Emulsions and Emulsion Stability. J. Sjoblom, editor. Marcel Dekker, New York.
Deleage, G. 1993. DICROPROT, version 2.5. Institute of Biological Chemistry of Proteins, Lyon, France. http://www.ibcp.fr. [Online].
Dockal, M., D. C. Carter, and F. Ruker. 2000. Conformational transitions of the three recombinant domains of human serum albumin depending on pH. J. Biol. Chem. 275:3042–3050.
Gaggelli, E., F. Berti, N. D'Amelio, N. Gaggelli, G. Valensin, L. Bovalini, A. Paffetti, and L. Trabalzini. 2002. Metabolic pathways of carcinogenic chromium. Environ. Health Perspect. 110:733–738.[Medline]
Gelamo, E. L., C. H. T. P. Silva, H. Imasato, and M. Tabak. 2002. Interaction of bovine (BSA) and human (HSA) serum albumins with ionic surfactants: spectroscopy and modeling. Biochim. Biophys. Acta. 1594:84–99.[CrossRef][Medline]
Glatter, O., and O. Krathy. 1982. Small Angle X-Ray Scattering. O. Glatter and O. Krathy, editors. Academic Press, London, UK.
Guinier, A., and G. Fournet. 1955. Small Angle Scattering of X-Ray. A. Guinier and G. Fournet, editors. Wiley, New York.
Guo, X. H., and S. H. Chen. 1990. The structure and thermodynamics of protein-SDS complexes in solution and the mechanism of their transports in gel electrophoresis process. Chem. Phys. 149:129–139.[CrossRef]
Guo, C. C., H. P. Li, X. B. Zhang, and R. B. Tong. 2003. Synthesis of meso-5, 10, 15, 20-tetra [4-(N-pyrrolidinyl)phenyl] porphyrin and its interaction with bovine serum albumin. Chem. J. Chinese Universities. 24:282–287.
Ibel, K., R. P. May, K. Kirschner, H. Szadkowski, E. Mascher, and P. Lundahl. 1990. Protein-decorated micelle structure of sodium-dodecyl-sulfate-protein complexes as determined by neutron scattering. Eur. J. Biochem. 190:311–318.[Medline]
Improta, S., J. K. Krueger, M. Gaute, and R. A. Atkinson. 1998. The assembly of immunoglobulin-like modules in titin: implications for muscle elasticity. J. Mol. Biol. 284:761–777.[CrossRef][Medline]
Jones, M. N. 1975. A theoretical approach to the binding of amphipathic molecules to globular proteins. Biochem. J. 151:109–114.[Medline]
Kelley, D., and D. J. McClements. 2003. Interactions of bovine serum albumin with ionic surfactants in aqueous solutions. Food Hydrocolloids. 17:73–85.[CrossRef]
Kelly, S. M., and N. C. Price. 1997. The application of circular dichroism to studies of protein folding and unfolding. Biochim. Biophys. Acta. 1338:161–185.[CrossRef][Medline]
Ladokhin, A. S., M. E. Selsted, and S. H. White. 1999. CD spectra of indolicidin antimicrobial peptides suggest turns, not polyproline helix. Biochemistry. 38:12313–12319.[CrossRef][Medline]
Li, G., Y. Lin, Y. Gu, J. Shen, and J. Yang. 1985. The determination of the second CMC of surfactants by fluorescence. Journal of Shandong University. 4:111–115 (Natural Science Edition).
Liu, D. H., D. A. Williamson, M. L. Kennedy, T. D. Williams, M. M. Morton, and D. R. Benson. 1999. Aromatic side chain-porphyrin interactions in designed hemoproteins. J. Am. Chem. Soc. 121:11798–11812.[CrossRef]
Lundahl, P., E. Greijer, M. Sandberg, S. Cardell, and K. O. Eriksson. 1986. A model for ionic and hydrophobic interactions and hydrogen-bonding in sodium dodecyl sulfate-protein complexes. Biochim. Biophys. Acta. 873:20–26.[CrossRef]
Mattice, W. L., J. M. Riser, and D. S. Clark. 1996. Conformational properties of the complexes formed by proteins and sodium dodecyl sulfate. Biochemistry. 15:4264–4272.[CrossRef]
May, S., and A. Ben-Shaul. 2001. Molecular theory of the sphere-to-rod transition and the second CMC in aqueous micellar solutions. J. Phys. Chem. B. 105:630–640.
McCoy, M. A., and D. F. Wyss. 2002. Structures of protein-protein complexes are docked using only NMR restraints from residual dipolar coupling and chemical shift perturbations. J. Am. Chem. Soc. 124:2104–2105.[CrossRef][Medline]
McLachlan, A. D., and J. E. Walker. 1977. Profile analysis: detection of distantly related proteins. J. Mol. Biol. 112:543–558.[CrossRef][Medline]
Nozaki, Y., J. A. Reynolds, and C. Tanford. 1974. The interaction of a cationic detergent with bovine serum albumin and other proteins. J. Biol. Chem. 249:4452–4459.
Price, N. C. 2000. Conformational issues in the characterization of proteins. Biotechnol. Appl. Biochem. 31:29–40.[CrossRef]
Ray, S., and A. Chakrabarti. 2003. Erythroid spectrin in miceller detergents. Cell Motil. Cytoskeleton. 54:16–28.[CrossRef][Medline]
Reynolds, J. A., and C. Tanford. 1970a. Binding of Dodecyl Sulfate to Proteins at High Binding Ratios. Possible Implications for the State of Proteins in Biological Membranes. Proc. Natl. Acad. Sci. USA. 66:1002–1007.
Reynolds, J. A., and C. Tanford. 1970b. The Gross Conformation of Protein-Sodium Dodecyl Sulfate Complexes. J. Biol. Chem. 245:5161–5165.
Shinagawa, S., K. Kameyama, and T. Takagi. 1993. Effect of salt concentration of buffer on the binding of sodium dodecyl sulfate and on the viscosity behavior of the protein polypeptide derived from bovine serum albumin in the presence of the surfactant. Biochim. Biophys. Acta. 1161:79–84.[CrossRef][Medline]
Shirahama, K., K. Tsujii, and T. Takagi. 1974. Free-boundary electrophoresis of sodium dodecyl sulfate-protein polypeptide complexes with special reference to SDS-polyacrylamide gel electrophoresis. J. Biochem. (Tokyo). 75:309–319.
Sun, C. X., J. H. Yang, X. Wu, B. Y. Su, and S. F. Liu. 2004. Fluorescent enhancement effect in terbium-gadolinium-protein-cetylpyridine bromide system and its application for the determination of protein at nanogram level. Chem. Phys. Lett. 398:343–350.[CrossRef]
Tao, W. S. 1981. Protein Macular Basic. The People's Education Press, China.
Turro, N. J., and X. G. Lei. 1995. Spectroscopic probe analysis of protein-surfactant interactions: the BSA/SDS system. Langmuir. 11:2525–2533.[CrossRef]
Valstar, A., M. Almgren, W. Brown, and M. Vasilescu. 2000. The interaction of bovine serum albumin with surfactants studied by light scattering. Langmuir. 16:922–927.[CrossRef]
Wang, H. Y., Q. S. Hui, L. D. Liu, Y. Sun, and L. Ma. 2000. Simultaneous determination of tryptophan and tyrosine by second order derivative fluorimetry. Spectroscopy and Spectral Analysis. 6:427–430.
This article has been cited by other articles:
 |
|
 |
|
  A. Feis, L. Tofani, G. De Sanctis, M. Coletta, and G. Smulevich Multiphasic Kinetics of Myoglobin/Sodium Dodecyl Sulfate Complex Formation Biophys. J., June 1, 2007; 92(11): 4078 - 4087. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
