Distribution of cyclic AMP-dependent protein kinase in the bovine cornea

Soluble and particulate fractions of bovine corneal epithelium, stroma and endothelium were prepared and assayed for protein kinase activity. All preparations exhibited measurable activity in the absence of cyclic AMP (cyclic AMP-independent activity) as well as significant enzyme stimulation in its presence (cyclic AMP-dependent activity). The epithelial layer contained over 90% of the total corneal cyclic AMP-dependent protein kinase activity, almost all of it in the soluble fraction. In contrast, over one-third of the endothelial activity was expressed by the particulate fraction. All preparations showed high affinity and high specificity for, cyclic AMP in terms of binding cyclic [ 3H]AMP and stimulating protein kinase activity. Elution characteristics of soluble preparations on DEAE cellulose columns demonstrated that epithelial and endothelial layers contained predominantly ‘Type II cyclic AMP-dependent protein kinase, whereas stroma had the ‘Type I enzyme. Each preparation studies also exhibited endogenous substrates for cyclic AMP-dependent protein kinase.