A variant alkaline phosphatase detected in a patient with lung cancer

A variant alkaline phosphatase (ALP), with heat-sensitivity characteristics similar to that of the bone type, was found in the serum of a patient suffering from lung cancer. In disc polyacrylamide gel electrophoretic studies most of this enzyme had migrated to the region corresponding to liver ALP, with the remainder affecting bone ALP. Like kidney ALP, this ALP was markedly inhibited by 0.5 mmol/l L-cysteine. The K(m) of this ALP for p-nitrophenylphosphate was 0.39 mmol/l, similar to that of kidney ALP. The sugar moiety of this enzyme bore greater resemblance to that of kidney ALP than liver or bone ALP. However, immunoprecipitation of this particular ALP was strong with a monoclonal antibody against liver ALP and moderate with an antibody against bone ALP.