Cyclic AMP dependent protein kinase activity was demonstrated in extracts of epithelial cells and cortical fibers of bovine eye lens. The histone fractions can be phosphorylated by these enzymes. Highest phosphorylation was obtained with f2b and f1 histone fractions. The Km values of the epithelial and cortical enzymes were very similar with all histone fractions. Protein kinase in the two extracts had a similar affinity to ATP and showed a pH optimum at 6·0-6·2. The enzymes were activated by cyclic AMP and the concentration of cyclic AMP necessary to half maximal activation was similar for both enzymes: 5×10-8 m for the epithelial enzyme and 9×10-8 m for the cortical enzyme. The magnitude of activation, however, was very different. The activity of the epithelial enzyme was increased 5-8-fold, while that of the cortical enzyme up to 25-fold. The high cyclic AMP sensitivity of the cortical enzyme was accompanied by a relatively high cyclic AMP binding capacity.
ASJC Scopus subject areas
- Sensory Systems
- Cellular and Molecular Neuroscience