α-Actinin from red and white porcine muscle

Abstract

Properties of purified α-actinin prepared from red and white sections of porcine semitendinosus muscle were compared. Although Z-lines were 2.25 times wider in red semitendinosus than in white semitendinosus, identical yields of α-actinin were obtained from these two sections of the semitendinosus. Since α-actinin is located in the Z-line, this result indicates that the Z-line contains proteins in addition to α-actinin. Reconstituted actomyosin prepared from red semitendinosus had a lower Mg 2+-modified ATPase activity and a slower rate of turbidity increase than reconstituted actomyosin made from white semitendinosus; this result and the fact that red semitendinosus had wider Z-lines than the white semitendinosus confirmed that red semitendinosus contained a predominance of red fibers, whereas the white semitendinosus contained a predominance of white fibers. Red α-actinin contained more aspartic acid than white α-actinin; this difference was mainly responsible for red α-actinin having 17 more negatively charged amino acids per 1000 total amino acids than white α-actinin. Because of this difference in negatively charged, amino acid side chains, red α-actinin could be separated from white α-actinin by DEAE-cellulose chromatography or polyacrylamide gel electrophoresis. Red α-actinin did not differ from white α-actinin in sedimentation pattern (both 6.1 S), in circular dichroic spectra (both about 59% α-helical), in rate of digestion by trypsin, or in ability to increase the Mg 2+-modified ATPase activity or rate of turbidity increase in suspensions of either red or white reconstituted actomyosin. The properties of porcine α-actinin are very similar to those of rabbit α-actinin, but the physiological role of α-actinin remains undetermined.