Ca²⁺-Dependent Proteolytic Modification of the Camp-Dependent Protein Kinase in Drosophila Wild-Type and Dunce Memory Mutants

Abstract

Two cAMP-dependent protein kinases with different activation constants were separated from Drosophila melanogaster head extracts. Both are only found in nervous tissue. The first cAMP-dependent kinase, with M_r = 190,000, has been already characterized as tetrameric Drosophila type II cAMP-dependent protein kinase R₂C₂. The second purified cAMP-dependent protein kinase, with M_r = 80,000, is dimeric in structure R_PC, and the cAMP-concentration required for half maximal activation is 4 fold lower than for the type II kinase. The generation of R_P can be stimulated in vitro by addition of exogenous calcium and is due to an endogenous Ca²⁺-dependent protease that selectively degrades the regulatory subunit. Extraction in the presence of various protease inhibitors does not affect the amounts of R_p, suggesting that the observed quantitative change in R_P occurs in vivo. The amounts of R_P in the nervous tissue of the memory mutants dunce' and dunce², which have increased cAMP levels, are different from the amount of R_P in wild-type flies. Also treatments of wild-type flies with drugs affecting cAMP-metabolism and acetylcholine levels led to amounts of R_P different from untreated flies.

Key Words:

• cAMP-cascade
• enzyme regulation
• Co²⁺ -dependent protease
• neural plasticity