Enzymatic microassay of pyridoxal-5'-phosphate using L-tyrosine apodecarboxylase and L-(1-14C) tyrosine.

A microassay for pyridoxal-5'-phosphate (PLP) is described, which incorporates both the enzymatic and radioisotopic techniques. The method is based upon the stoichiometric decarboxylation of L-(1-14C) tyrosine by L-tyrosine apodecarboxylase and PLP. This method is an extensive modification of the ones reported by us previously, the main features of this present method being the ease of preparation of the enzyme extract and the substrate, elimination of the preincubation period and shortening of the 14CO2-trapping step. The assay as described here is rapid, highly sensitive and specific.