Pyridoxal-5′-phosphate and alkaline phosphatase

✍ Scribed by Lawrence Lumeng

• Publisher: John Wiley and Sons
• Year: 1986
• Tongue: English
• Weight: 287 KB
• Volume: 6
• Category: Article
• ISSN: 0270-9139
• DOI: 10.1002/hep.1840060231

✦ Synopsis

Markedly increased circulating concentrations of pyridoxal-5'-phosphate (PLP) were found in each of 14 patients representing all clinical forms of bypophosphatasia, an inborn error characterized by deficient activity of the tissue-nonspecific (bone/liver/kidney) isoenzyme of alkaline phosphatase (AP). The mean PLP concentration in plasma was 1,174 nM (range. 214 to 3,839 nM) in the patients and 57 2 26 nM (mean 2 S.D.) in 38 control subjects. In four affected children, urinary excretion of the PLP degradation product, 4-pyridoxic acid, was unremarkable during consumption of normal quantities of dietary vitamin Bs.

Our findings identify increased circulating PLP concentration as a marker for hypophosphatasia and provide further evidence that tissue-nonspecific AP acts in vitamin Be metabolism. Tissue-nonspecific AP appears to function as an ectoenzyme to regulate extracellular but not intracellular levels of PLP substrate. Performing assays of circulating PLP concentrations alone to assess vitamin Be nutrition may be misleading in disorders associated with altered AP activity.