Ionic strength and myofibrillar protein solubilization.

Myofibrils from bovine longissimus muscle were obtained at 2 h postmortem and incubated in .10 to .35 M ionic strength buffers under various conditions in vitro. Increasing ionic strength or increasing the incubation time from 1 to 72 h decreased the turbidity of suspensions of myofibrils and increased myofibrillar solubilization (P less than .01 for both measures). The use of KCl or NaCl to elevate ionic strength gave essentially identical results, but lactate generally was ineffective in changing either the percentage myofibrillar solubilization or the turbidity of suspensions of myofibrils. Gel electrophoresis under denaturing conditions indicated that KCl was more effective than NaCl in causing the release of C-protein from myofibrils, and both salts were quite effective in dissociating M-protein, actin, troponin-T, tropomyosin, myosin light chain-3 and a 30,000-dalton molecular weight protein from myofilaments. Small increases in alpha-actinin also were observed, especially in samples incubated for 72 h. Substantially more myosin light chain-3, tropomyosin (or paratropomyosin) and troponin-T, and less actin and the 30,000-dalton protein, were released in samples incubated at pH 5.5 than at pH 7.0 (P less than .05). Electron micrographs indicated loss of thick filament ultrastructure after incubation for 24 h in either .1 or .3 M ionic strength, but the Z-lines were largely unaffected. In samples that had first been incubated with trypsin for 10 min, the Z-lines were virtually indistinguishable at .1 M ionic strength, and absolutely no myofibrillar structures could be discerned in samples incubated in .3 M ionic strength buffer.(ABSTRACT TRUNCATED AT 250 WORDS)