Mechanistic Studies of cAMP-Dependent Protein Kinase Actio

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Abstract
The chemistry of the catalytic subunit of type-II cAMP-dependent protein kinase has been probed employing kinetic studies, magnetic resonance methods, and stereochemical techniques. The active complex is an enzyme-ATP-metal bridge. The enzyme acts on the Δ-isomer of β,γ-bidentate Co(NH3)4 ATP and the A isomer of the Mg++ complex of β-thio ATP. Through a combination of kinetic and NMR studies using a variety of hepatapeptide substrates, α-helical, β-pleated sheet, and some β-turn conformations have been ruled out for the enzyme-bound peptide substrates. However, β2–5 and β3–6 turn conformations remain possible and are being examined further. Finally, the introduction of a new peptide substrate Leu-Arg-Arg-Tyr(o-NO2)-Ser-Leu-Gly, which on phosphorylation undergoes a spectral change that can be readily monitored, has permitted extensive kinetic studies with chemically modified catalytic subunits which are helping to clarify the active site requirements of the enzyme.

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