STUDIES ON BOVINE NATURAL ACTOMYOSIN .2. PHYSICO-CHEMICAL PROPERTIES AND TENDERNESS OF MUSCLE

SUMMARY: Studies were made of physicochemical characteristics of natural actomyosin from bovine longissimus of different post‐mortem ages and tenderness classifications. Reduced viscosity, ATP sensitivity, and “actin” content (polyethylene sulfonate treatment) were higher for natural actomyosin prepared from muscle 12‐24 hr post‐mortem than from pre‐rigor muscle, which confirms previous reports for rabbit natural actomyosin. A higher actin to myosin ratio in actomyosin from muscle 12‐24 hr was therefore postulated. A stronger interaction of actin and myosin in actomyosin from muscle 12‐24 hr post‐mortem than from pre‐rigor or aged muscle was also suggested by reduced viscosity and ultracentrifugation data. Reduced viscosity differences between actomyosins from tough and tender muscle suggested a higher gel character in actomyosin from tough muscle. This possibly indicated a higher content of α‐actinin. No consistent differences in ATP sensitivity, myosin and actin content of natural actomyosin of tough and tender muscle were found. Natural actomyosin from muscle aged post‐mortem showed the appearance during analytical ultracentrifugation of an additional component which sedimented at about 11S to 12S. This component appeared in the actomyosin prepared from tender muscle after 24 hr but did not appear until 10 days in the actomyosin from tough muscle. Copyright © 1969, Wiley Blackwell. All rights reserved