CALMODULIN-BINDING PROTEINS AND CALCIUM CALMODULIN-REGULATED ENZYME-ACTIVITIES ASSOCIATED WITH BRAIN ACTOMYOSIN

Calcium‐ and calmodulin‐regulated ATPase and protein kinase activities are shown to be strongly associated with brain actomyosin. Similar enzymatic activities and an invariable polypeptide profile on sodium dodecyl sulfatepolyacrylamide gel electrophoresis were obtained for brain actomyosin taken through a solubilization‐precipitation cycle (1.0–0.1 M KC1), or precipitated from buffers containing 1% Triton X‐100 or 10 mM EDTA and 10 mM EGTA. These data suggest a specific complex of brain actomyosin with a protein kinase similar to calmodulin‐dependent kinase II, a 190‐kDa calmodulin‐binding protein (P190), and a calmodulin‐like polypeptide. P190 was the major substrate for endogenous calcium‐dependent phosphorylation. 125I‐Calmodulin overlay technique revealed four major calmodulin‐binding polypeptides associated with brain actomyosin: 50‐and 60‐kDa subunits of the calmodulin‐dependent kinase II, P190, and a high molecular weight polypeptide which is probably fodrin. A fraction enriched in P190 had Ca2+‐ and calmodulin‐stimulated MgATPase activity, but not myosin‐like K‐EDTA ATPase activity. The lack of immunological crossreactivity between brain myosin heavy chain and P190 confirmed that they are distinct molecules. Copyright © 1990, Wiley Blackwell. All rights reserved