Demonstration of adenylate-kinase activity in hepatic microsomes. Relevance to Ca2+ uptake.

It is demonstrated that the hepatic microsomal fraction contains significant adenylate-kinase activity. This explains a paradoxical ADP-stimulated Ca2+ uptake into microsomal vesicles which is inhibited when adenylate kinase is inhibited. The presence of adenylate kinase in the microsomal fraction helps to prevent sudden drops in ATP level, and thus has a stabilizing effect on the many ATP-dependent reactions carried out in this subcellular compartment.