GLYCOLYSIS-CITRIC ACID CYCLE INTERRELATION - A NEW APPROACH AND SOME INSIGHTS IN CELLULAR AND SUBCELLULAR COMPARTMENTATION

In the development of an integrated approach to study metabolic compar tmentation and regulation in brain, we have emphasized the importance, versatility, and need to exploit the recent methodological advances i n (1) NMR spectroscopy, (2) primary cultures of neurons and glial cell s, and (3) subcellular fractionation (especially brain mitochondrial i solation). The integrated approach has the advantage of being able to draw data and inferences based on some combination of results derived from in vivo, cellular, and subcellular studies. For example, some in vivo NMR data may suggest that an enzymatic step may be rate-limiting in a particular pathway. This information may be used to frame testabl e hypotheses and questions that can be investigated in experiments inv olving primary cultures of neural cells and subcellular fractions. Sub sequently, the data from such in vitro studies could serve as the base s for constructing the hypothetical framework for predicting the regul atory role, in vivo, of the enzyme in the pathway. We have discussed t he known as well as the as yet ill-defined facets of the cellular and subcellular aspects of the glycolysis-citric acid cycle interrelation and have attempted to illustrate how such an integrated approach could be applied to generate testable hypotheses for investigating the mech anisms concerned with metabolic compartmentation and regulation in bra in. In the process of the illustration, we discuss some of the evidenc e in support of the general hypothesis that the transfer of reducing e quivalents across the inner mitochondrial membrane plays a major role in mediating the coupling of the glycolytic flux to that of the citric acid cycle. We have given some indications as to how this hypothesis could be further investigated employing our approach. Moreover, we hop e that other workers will find this integrated approach useful in desi gning multidisciplinary studies to investigate mechanistic issues rela ted to this important theme.