Inhibition of calcium-dependent actin gelation by actin-binding protein from platelets

Various proteins related to cell contraction have been extracted from human platelets. Of these, a protein (48K) with the molecular weight of 48,000 and one with the molecular weight of 47,000 (P47) often migrate together with actin on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. We studied the biochemical characteristics of the 48K protein, purified by actin affinity and DEAE-Sepharose chromatography. The 48K protein did not react with anti-actin antibody or peroxidase-labelled actin. The protein inhibited the calcium-dependent gelation of actin. The 48K protein seemed to be a regulatory protein involving cell contraction not identified before.