Determination of the specific radioactivity of [C-14]lactate by enzymatic decarboxylation and (CO2)-C-14 collection

We present an enzymatic method for the determination of L-[C-14]lactate specific radioactivity in complex biological samples containing other radiolabeled compounds. The method is based on the conversion of L-lactate to L-pyruvate by lactate oxidase (no EC number assigned) and the decarboxylation of L-pyruvate by pyruvate oxidase (EC 1.2.3.3). The (CO2)-C-14 produced by the enzymatic decarboxylation of pyruvate is quantitatively captured in a CO2 trap and its radioactivity is measured. The method is simple, specific, and precise (2% relative SD). It can be conveniently used for routine multiple determinations of L-[C-14]lactate specific radioactivity in tracer metabolic studies. Under specified conditions, the method can also be used to determine the specific radioactivity of L-[C-14]pyruvate. (C) 1997 Academic Press.