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

We present an enzymatic method for the determination of L-[14C]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 14CO2 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-[14C]lactate specific radioactivity in tracer metabolic studies. Under specified conditions, the method can also be used to determine the specific radioactivity of L-[14C]pyruvate.