216 PROTEIN KINASES IN BROWN ADIPOSE TISSUE OF DEVELOPING RATS. SEPARATION, SUBSTRATE SPECIFICITIES AND CHANGES IN INDIVIDUAL ACTIVITIES DURING PERINATAL DEVELOPMENT

Abstract

Brown adipose tissue of the rat undergoes a very rapid process of functional and morphological maturation perinatally,reaches a peak in its differentiation and functional capacity 1 to 2 weeks after birth and its involution commences at 3 to 4 weeks of age. The regulation of the tissue function, i.e. heat production, and of its maturation, are hormone-mediated and are associated with the phosphorylation and de-phosphorylation of specific proteins and enzymes. The diversity of the protein kinase system, and yet its specificity to carry out phosphorylations associated with a particular function, is reflected in that nine activities could be separated from the tissue soluble extracts on polyacrylamide. Five of the enzymes were histone kinases,two preferred phosvitin or casein, and arginine-rich histone and protamine were rapidly phosphorylated by the remaining two. Cyclic AMP stimulated the phosphorylation of histones but not that of the other proteins. The pattern of activity changes during development was different with different protein substrates, as was the relative abundance of each individual enzyme. It is speculated that there are three classes of protein kinases in brown fat: a) those related to the tissue's function,e.g. lipolysis and glycogenolysis ; b) those related to proliferation and cell division ; c) those related to the tissue's differentiation, e.g. enzyme inductions.