The Myosin Filament: XI Filament Assembly

Abstract

The critical parameters required for the assembly of myosin filaments with a length distribution comparable to that for native myosin filaments were examined. It was found that: a) Two steps are required in the dilution of a myosin solution from 0 .6M KC1 to 0.15M KC1. In Step I the KC1 concentration is reduced from 0.6 to 0.3M KC1 and in Step II from 0.3 to 0.15M KC1. b) The rate of change of KC1 required for Step I is different than that required for Step II. c) Increasing the total time of dilution in either Step I or II alone leads to an increase in length and a broadening of the length distribution. In Step I assembly of myosin molecules into non sedimentable units occurs. These may be the basic units from which the filaments are assembled in Step II. d) Rapid dilution in Step I alone has no effect on the length distribution obtained at 0.15M KC1, but rapid dilution in Step II alone leads to short filaments (about 0.6 urn), e) Increasing the time of dilution in Step II alone to 3 hrs or 6 hrs gives a bimodal distribution in lengths with one peak at about 0.8 urn and the other at about 2.2 urn. f) The length distribution obtained at 0.15M KC1 is not critically dependent on information contained in the portion of the filament previously assembled in Step II, but is critically dependent on the rate of change of KC1 concentration during the assembly of the rest of the filament.