A Variant Alkaline Phosphatase Detected in a Patient with Lung Cancer

Abstract

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/1 L-cysteine. The K(m) of this ALP for p-nitrophenylphosphate was 0.39 mmol/1, 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, immunoprécipitation of this particular ALP was strong with a monoclonal antibody against liver ALP and moderate with an antibody against bone ALP.

Alkaline Phosphatase: A Reliable Endogenous Partner for Drug Delivery and Diagnostics

“…ALP is also competitively and reversibly inhibited by inorganic phosphate, the product of dephosphorylation reaction. Furthermore, l-cysteine, l-tryptophan, l-phenylalanine, and lleucine were found to inhibit human TSAP, [31,108] while lhomoarginine was shown to be a TNAP inhibitor. [109,110] The mechanism involved the interaction of Arg residue and Zn1 in the ALP active site with l-amino acids through their carboxylic and amine groups, respectively, and thus interfering the hydrolysis of phosphate-ALP intermediate.…”