The Specificity of Chicken Gizzard Actin

Abstract

Actin was obtained in high purity and with a high yield from chicken gizzard muscle. 1) The amino acid composition of gizzard actin was almost identical with skeletal actin. Gizzard actin contained approximately 6 cysteinyl residues per mol of actin, although skeletal actin had 5 cysteinyl residues per mol. 2) Two forms of polymerized actin, F-type and f-type, were obtained depending on whether or not calcium ions were present in the medium used for extraction and purification. F-type actin was almost identical with skeletal muscle F-actin in sedimentation coefficient, viscosity, and activation of the Mg²⁺ ATPase of myosin. f-type actin showed charactristics similar to those of plasmodium Mg-polymer; low viscosity, steady ATP-splitting and electron micrographic appearances. 3) When dialyzed aginst a buffer without added calcium, gizzard G-actin which was otherwise capable of polymerizing to F-type, was transformed to f-type-forming G-actin, with concomitant loss of a considerable amount of bound calcium. 4) Skeletal and gizzard actins were cleaved by 2-nitro-5-thiocyanobenzoic acid at cysteine residues, and then analyzed by SDS-polyacrylamide gel eleotrophoresis. At least two fragments of cleaved gizzard actin showed similar but nonidentical electrophretic mobility as compared with the corresponding fragments of skeletal actin.