Determination of the Specific Radioactivity of [14C]Lactate by Enzymatic Decarboxylation and14CO2Collection

We present an enzymatic method for the determination ofl-[14C]lactate specific radioactivity in complex biological samples containing other radiolabeled compounds. The method is based on the conversion ofl-lactate tol-pyruvate by lactate oxidase (no EC number assigned) and the decarboxylation ofl-pyruvate by pyruvate oxidase (EC 1.2.3.3). The14CO2produced by the enzymatic decarboxylation of pyruvate is quantitatively captured in a CO2trap and its radioactivity is measured. The method is simple, specific, and precise (2% relative SD). It can be conveniently used for routine multiple determinations ofl-[14C]lactate specific radioactivity in tracer metabolic studies. Under specified conditions, the method can also be used to determine the specific radioactivity ofl-[14C]pyruvate.