Calcium-Regulated Protein Kinases and Phosphatases

Huang, C

Abstract

(1) The calmodulin-dependent protein phosphatase is activatable by Ni(II) in the absence of calmodulin provided some Ca(II) is present. The mechanism of activation is consistent with the random binding of 2 Ni(II) ions which leads to a conformational rearrangement. Experimental and theoretical considerations seem to rule out the existence of an activated intermediate that is reversible to the inactive state on removal of Ni(II). The time-dependent binding of 2 Ni(II) ions to the phosphatase has been confirmed by direct binding studies using radioactive Ni. Phosphorylation of the phosphatase by protein kinase C is further verified by using the catalytic subunit of protein kinase C, the M kinase. (2) A Ca(II)-inhibited 56,000 MW phosphatase has been purified to greater than 80% purity. Survey of various chromatographic fractions of bovine brain reveals the presence of several Ca(II)- sensitive protein phosphatases whose MW range from 20,000 to 200,000. (3) Anomalous stoichiometry of protein-ligand and protein- protein interactions as determined by the continuous variation method is discussed for 2 cases: positive cooperativity and ordered reconstitution of unidentical enzyme subunits. It is shown that apparent stoichiometry greater than the true value may be observed at intermediate levels of total protein and ligand. These anomalous stoichiometries should provide clues to the mode of interaction of the components involved. (4) An improved procedure for the calculation of King-Altman patterns for kinetic reaction schemes has been developed. In this method, each scheme is broken down into 2 diagrams. In one diagram, a selected branch is deleted, while in the other diagram the selected branch must always be present. In the latter diagram, the selected branch is compressed into a point. The sub-diagramming procedure can be repeated as many times as necessary until the resultant diagrams can all be easily calculated.