A study of G-actin

Abstract

1. 1. Starch-gel electrophoresis at pH 8.5 and sedimentation analysis of carefully prepared rabbit G-actin indicate that this protein is heterogeneous. Upon reduction it behaves as a homogeneous protein.

2. 2. Identical starch-gel diagrams were obtained for skeletal muscle of the rabbit, the breast muscles of the pigeon, and heart and skeletal muscles of the ox.

3. 3. Arguments are advanced for the view that the observed heterogeneity of fresh G-actin might well find its origin in intramolecular disulfide linkages, occurring in some molecules, though not always between the same areas within each molecule, and leading to the formation of a restricted number of aggregates upon denaturation of the non-reduced protein.

4. 4. The molecular weight of G-actin was determined at 58 500 ± 1000.

5. 5. Phenylalanine was found to be the C-terminal amino acid residue of G-actin, in confirmation of observations by others. “Non mole to mole” ratios were found in determining the N-terminal residue. This residue may be blocked by an acetyl group.

6. 6. The amino acid composition of G-actin was determined and found to agree excellently with data published by others.