Biophysical Journal 61: 631-638 (1992)
© 1992 the Biophysical Society

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The efficiency of malachite green, free and protein bound, as a photon-to-heat converter

Guilherme L. Indig ^*, Daniel G. Jay  and Joseph J. Grabowski ^*

Department of Chemistry, Harvard University, Cambridge, Massachusetts 02138
Department of Cellular and Developmental Biology, Harvard University, Cambridge, Massachusetts 02138

ABSTRACT

Dye assisted laser inactivation of proteins has been found to be a methodology that can achieve high selectivity. Despite the fact that the methodology is successful, knowledge of the detailed inactivation mechanism would allow full optimization of this technique. Here, pulsed-laser photoacoustic calorimetry is used to study the photophysical properties, principally the heat release behavior, of protein bound malachite green. We found that when bound to bovine serum albumin the dye is a good photon-to-heat converter, but 2.6% of the absorbed photon energy (_exc = 624 nm) is not released as heat in less than 10 µs. This observation suggests that a mechanism other than simple heat-induced inactivation may be the principle process; a long lived excited triplet state of malachite green (or species derived from it) is postulated to play a major role.