A method for the measurement of specific lactate radioactivity in biological samples is presented. It is based on the following steps: (a) enzymatic conversion of lactate to pyruvate, (b) pyruvate conversion to 2,4dinitrophenylhydrazone, (c) concentration-separation of the latter in reusable Amberlite XAD-7 polymeric adsorbent columns, and finally (d) estimation of the radioactivity thus retained compared with that of enzymatically untreated aliquots of the same samples. Specificity was ensured by the use of lactate dehydrogenase as specific recognizing agent for lactic acid. No interference from glucose, lactate, or amino acids was observed. The method presented is simple and can be applied in routine multiple estimations of lactic acid radioactivity in coniunction with the enzymatic measurement of lactate in biological samples in tracer metabolic studies. Q 1985 Academic Press, Inc.
' Supported by a grant from the "Comision Asesora para la Investigation Cientifica y Tkxica" from the Government of Spain and a grant from the University of Palma de Mallorca.
Methods
All reagents used were of analytical grade. Labeled materials were obtained from The Radiochemical Center (Amersham, U. IL). Biochemical standards and reagents were ob-