A Convenient Method for the Determination of Metabolically Liberated C¹⁴O₂

Abstract

Because of the widespread use of carbon-14-labeled compounds in biochemical studies in which C¹⁴O₂ is liberated, many ingenious methods have been devised for the trapping of the C¹⁴O₂ for purposes of determining the radioactivity. We do not intend to review the literature on the subject. For a number of years our laboratory has been engaged in the study of γ-aminobutyric acid and the enzyme which fauns it from L-glutamic acid, glutamic decarboxylase (see [¹]). Both γ-aminobutyric acid and the enzyme occur uniquely in the central nervous system of various vertebrate species. Since the decarboxylase has a relatively low turnover number under the optimal in vitro conditions, it is necessary to employ an extremely sensitive method, if small portions of nervous tissue are to be studied. Albers devised a micro method by which small amounts of C¹⁴O₂ liberated from L-glutamic acid-C¹⁴ were trapped in Hyamine base and counted in a liquid scintillation counter [²]. Our method is essentially a modification of the latter procedure which enables the C¹⁴O₂ to be trapped in Hyamine base contained in a regulation size counting vial, and to be counted under standard conditions without any additional pipetting, thus avoiding the inaccuracies introduced by further transfers.

This study was supported in part by grants from the National Institute of Neurological Diseases and Blindness, National Institutes of Health, and a grant from the National Association for Mental Health, Inc. Presented at the Seventh Symposium on Advances in Tracer Methodology, March, 1963.