5′-AMP hydrolysis by suspensions and homogenates of pancreatic islet cells from normal and cortisone-treated rats
Summary, in English
Suspensions of endocrine pancreas cells were prepared by shaking collagenase-isolated rat islets of Langerhans in calcium-free buffer. When incubated with 1.0 mM substrate at pH 7.4, the cells split, Pi from 5′-AMP at a rate of 87 nmol/h per μg DNA, and from β-glycerophosphate at a rate of 25 nmol/h per μg DNA Km for 5′ AMP was about 54 μM. Adenosine or theophylline inhibited the 5′-AMP hydrolysis. Homogenization of the cells increased the activity toward 5′-AMP by 23% and that toward β-glycerophosphate by 115%. Injecting rats with cortisone had no effect on the 5′-AMP hydrolysis by whole cells but significantly increased the activity in cell homogenates; the intracellular activity toward 5′-AMP was more than doubled by the cortisone treatment. Staining whole islet cells for 5′-AMP-splitting activity resulted in a demarcation of the cell periphery in control rats. Cells from cortisone-treated rats showed heavier deposits of reaction product, and their cell periphery did not stand out as clearly. It is suggested that 5′-nucleotidase is largely an ectoenzyme in normal rat islet cells. The cells also contain an as yet unidentified intracellular phosphatase that seems to be solely responsible for the increased hydrolysis of 5′-AMP in cortisone-treated rats.