Protein kinases in brown adipose tissue of developing rats. Electrophoretic separation and assay of soluble protein kinases on polyacrylamide gels and a study of their properties and changes during development.

Protein kinase activity was detected and assayed directly on polyacrylamide gels after disc electrophoresis of the 100,000 X g supernatant fraction of brown adipose tissue of infant rats. Nine major bands of activity were detected, eight of which could be stimulated by cAMP or inhibited by the cAMP-dependent protein kinase inhibitor protein. This electrophoretic technique revealed heterogeneity in the cAMP-dependent protein kinase activity eluted from DEAE-cellulose by high concentrations of salt, but not in the peak of activity eluted by low concentrations of salt. The catalytic properties and substrate specificities of the kinases in the various bands were studied while the enzymes were still in the gels. The activity in each band differed from each of the others in at least one of these properties. The activities of the protein kinases in brown fat changed as the animals grew, and each band exhibited a distinct and unique developmental pattern. The major changes in kinase activities occurred in the immediate post-parturition period, then at 15 days after birth and at weaning. These developmental stages coincide with the periods during which the tissue undergoes changes in the rate of its proliferation, differentiation, and functional activity.