A spectrophotometric assay of Zn(2+)-glycerophosphorylcholine phosphocholine phosphodiesterase using p-nitrophenylphosphorylcholine.

A direct spectrophotometric assay for the glycerophosphorylcholine phosphocholine phosphodiesterase requiring zinc ions for activity is described. This assay is based on the continuous measurement of p-nitrophenol produced from the enzymatic hydrolysis of p-nitrophenylphosphorylcholine. The assay method, which showed a good linearity with time and amount of protein, was found to be rapid, simple, and, at the same time, accurate and sensitive enough to allow the quantitation of nanomolar amounts of product. With an alkaline buffer containing Triton X-100, the Zn(2+)-glycerophosphorylcholine phosphocholine phosphodiesterase activity in the tissue homogenate can be directly and selectively measured by this technique. The specific activity of the phosphodiesterase in brain and kidney was determined to be 80 and 6.5 nmol/h mg protein, respectively, and much lower activity was present in other tissues.