Multiple Forms of Hepatic Adenosine 3':5' -Monophosphate Dependent Protein Kinase

Abstract

Cytoplasmic hepatic protein kinase is resolved into three fractions by chromatography on DEAE-Sephadex. Two of these fractions exhibit a sedimentation constant = 6.8 S, whereas the third component is 4.0 S. The activity of each 6.8S fraction is stimulated by adenosine 3':5'-mono-phosphate (cAMP) whereas that of the smallest protein kinase (4.0 S) is independent of this nucleotide. The 6.8S protein kinase that is present in the highest proportion can be dissociated to yield two protein kinase fractions, each of 4.0 S, whose activity is independent of cAMP, and neither of which is identical with the 4.OS protein kinase isolated by DEAE-Sephadex chromatography. On the basis of reconstitution experiments and on work recently presented by several laboratories it is interpreted that each 4.OS component represents a species of catalytic subunit of cAMP-dependent protein kinase, whereas the 6.8S protein is a holoenzyme(s) composed of catalytic and nucleotide-binding regulatory subunits. © 1971, American Chemical Society. All rights reserved.