[Soluble cAMP-dependent protein kinases from the rabbit myometrium].

Two isoforms (I and II) of soluble cAMP-dependent protein kinase with basal activity of 2.1 and 10.87 nmole of 32P/min/mg of protein, respectively, were detected in rabbit myometrium at functional rest. cAMP (5 microM) activates 1.5-fold both isoforms of the enzyme. The apparent Km values for ATP of isoforms I and II is 0.9 X 10(-5) M and 2.1 X 10(-5) M, respectively; Km for histone H1 are 0.15 and 0.29 mg/ml, respectively. The pH optimum for both isoforms lies at 7.3-7.6; the pI values are 5.0 and 5.5, respectively. Na-DS electrophoresis in polyacrylamide gel demonstrated that the molecular weight of the regulatory subunit (R) of isoform I is 47000, that of the catalytic subunit (C) is 31000. No difference in the electrophoretic mobility of C for forms I and II were found. The molecular weight of R II is 54000. Isoform II reveals the ability for autophosphorylation. The plot for the dependence of the reaction rate versus enzyme concentration is linear; up to 1.5 mole of 32P per mole of the holoenzyme is incorporated. The myometrium of pregnant rabbits contains one isoform of cAMP-dependent protein kinase which is identical to isoform II in terms of its elution profile on DEAE-cellulose, molecular weight of R, pI and the ability for autophosphorylation. The optimal conditions for the pregnant rabbit myometrium enzyme activity are as follows: pH 7.0-9.0, cAMP--10(-8) M, basal activity--3.68 nmole of 32P/min/mg of protein, cAMP activation--2.4-fold. The values of apparent Km for ATP and histone H1 are 5.6 X 10(-5) M and 0.42 mg/ml, respectively. During autophosphorylation 0.4 mole of 32P per mole of the holoenzyme is incorporated.