Proteolysis and structure of skeletal muscle actin.

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Abstract
Under standard conditions, G-actin [from rabbit muscle] was submitted to 9 proteases of varying specificity, and in each case the pattern of fragments produced was studied by NaDodSO4 [sodium dodecyl sulfate] gel electrophoresis. The actin monomer apparently consists of a large region (.apprx. 33 kilodaltons) and a small, easily degraded region (.apprx. 9 kilodaltons). The COOH terminus is in the large region. Consideration of primary sequence homologies, medium resolution maps of actin crystals and certain reactions of actin suggests that the NH2 terminus is in the small region, as is the negative sequence to which a divalent metal cation is normally chelated, but that the nucleotide-binding site is on the large region near the junction between the regions. These results make numerous properties of actin understandable.