Rat cerebral-cortex adenosine deaminase activity and its subcellular distribution

A radioisotopic assay for adenosine deaminase (EC 3.5.4.4) is described together with its application in investigating the activity of the enzyme in rat cerebral cortex. Activity of the adenosine deaminase was determined to be 115nmol/min per g of tissue, measured in isoosmotic sucrose dispersions of the neocortex, and to be 170nmol/min per g of tissue after treatment with Triton X-100. The enzyme was concluded to be largely cytoplasmic, with a K(m) of 54-57mum for adenosine. Action of the deaminase, and other aspects of the metabolism of adenosine in intact neocortical tissue, were quantitatively appraised on the basis of the newly determined characteristics.