Swelling and contraction of mitochondrial particles: a re-examination of the existence of a contractile protein extractable with 0.6 M-potassium chloride.

Abstract

Using ATP-induced superprecipitation as criterion for the presence of an actomyosin-like protein, an attempt was made to resolve the uncertainty concerning the 0.6 m -KCl-extractable “contractile protein” in mitochondria. It was not possible to extract from liver mitochondria, using 0.6 m -KCl under various conditions, a protein which would superprecipitate upon the addition of ATP (with or without added magnesium ions). The superprecipitation observed with heart sarcosome extracts, well characterized by its dependence on pH, ATP and magnesium ions, and by its modification with EDTA and heavy-metal ions, was not demonstrably different from that of heart muscle actomyosin. Even though electron micrographs of heart sarcosome pellets do not show the presence of myofibrillar material, it is concluded that the superprecipitation observed with the 0.6 m -KCl extracts is, in fact, due to extrasarcosomal actomyosin which cannot be eliminated by successive washings and differential centrifugation of the sarcosomes. Although extractions other than with 0.6 m -KCl may prove successful later in demonstrating the existence in the mitochondrial membrane of contractile macromolecules, the present results suggest that mitochondria do not contain a functional “contractile protein”.