Reinigung und Charakterisierung von cAMP‐abhängigen Proteinkinasen bei Hefen in einem Saccharomyces cerevisiae Wildstamm und ausgewählten Mutanten des cAMP‐Stoffwechsels

Protein kinases represent a diverse family of enzymes that play a critical role in regulation. Among nearly 100 known protein kinases, the cAMP‐dependent enzyme is best understood biochemically. Unlike other protein kinases, cAMP‐dependent protein kinase consists of two different types of subunits that dissociate, a regulatory subunit (R), which is the receptor for cAMP, and a catalytic subunit (C). In the absence of cAMP, the enzyme exists as an inactive tetramer, R 2 C 2. The binding of intracellular cAMP to the R subunit decreases the affinity of the R subunit for the C subunit by approximately four orders of magnitude and, under physiological conditions, leads to dissociation of the holoenzyme into R 2 (cAMP) 4 dimer and two free C subunits that are catalytically active. Mutants of the cAMP metabolism, adenylate cyclase and cell cycle mutants, provided further information about protein synthesis and cellular growth in Saccharomyces cerevisiae. The purified protein kinases were divided into different types according to their elution profiles from the DEAE‐cellulose matrix. Two types of cAMP‐dependent and two types of cAMP‐independent protein kinases were isolated from the wild strain. Differences in the activities of the kinases in the mutants showed a close relationship to the locus of the respective mutations in the cell‐cycle. Some properties of the protein kinases are discussed with respect to individual mutations.