Fiber depolymerization

¹ University of Warwick
² Albert Einstein College of Medicine
³ Drexel University
⁴ University of Chicago

^* To whom correspondence should be addressed. E-mail: m.s.turner{at}warwick.ac.uk.

Submitted on September 29, 2005
Revised on November 9, 2005
Accepted on 4 May 2006

	Abstract

Depolymerisation is, by definition, a crucial process in the reversible assembly of various biopolymers. It may also be an important factor in the pathology of sickle cell disease. If sickle hemoglobin fibers fail to depolymerize fully during passage through the lungs then they will reintroduce aggregates into the systemic circulation and eliminate or shorten the protective delay (nucleation) time for the subsequent growth of fibers. We study how depolymerization depends on the rates of end- and side-depolymerization, k_end and k_side, which are respectively the rates at which fiber length is lost at each end and the rate at which new "breaks" appear per unit fiber length. We present both an analytic mean field theory and supporting simulations showing that the characteristic fiber depolymerization time =1/(k_endk_side) depends on both rates, but not on the fiber length L, in a large intermediate regime 1<<k_side L²/k_end<<(L/d)², with d the fiber diameter. We present new experimental data which confirms that both mechanisms are important and shows how the rate of side depolymerization depends strongly on the concentration of CO, acting as a proxy for oxygen. Our theory remains rather general and could be applied to the depolymerization of an entire class of linear aggregates, not just sickle hemoglobin fibers.

Key Words: depolymerization, fiber, hemoglobin, nucleation, polymer, sickle