Adenosine 3':5'-monophosphate-dependent protein kinase from human placenta: characterization of the catalytic subunit.

The catalytic subunit of cAMP-dependent protein kinase (EC 2.7.1.37) was purified for the first time from human placenta by DEAE-cellulose and HTP chromatography. Sodium dodecyl sulfate/polyacrylamide gel electrophoresis showed a single band of average molecular weight of 42 kDa (SEM = 0.52). Kinetic experiments showed a Km for ATP of 12.6 +/- 1.2 mumol/l, for histone II-AS of 1.3 +/- 0.05 mg.ml-1, for kemptide of 11.4 +/- 4.4 mumol/l. The synthetic inhibitor IP20-amide showed a competitive mechanism of inhibition with a Ki of 5.0 nmol/l. The protein kinase inhibitors H7 and H9 showed an apparent Ki of 8.3 and 4.9 mumol/l respectively. Preparative isoelectric focusing revealed the presence of 5 different isoforms with an average pI of 6.17, 6.70, 7.15, 7.67, 8.9.