TRANSAMINATION PROCESSES PROMOTE INCOMPLETE GLUTAMINE OXIDATION IN SMALL-INTESTINE EPITHELIAL-CELLS

The aim of the present study was to examine the influence of glucose o n glutamine medabolism by intestinal epithelial cells. Cells were isol ated from the proximal, mid, and distal small intestine of male, fed m ts. The oxidation of [U-C-14]glutamine was greatest in the proximal sm all intestine, and the stimulatory effect of glucose on glutamine oxid ation was most pronounced in this segment also. Amino-oxyacetate, an a minotransferase inhibitor, did not influence the oxidation of glucose when present alone, but increased glucose oxidation when present simul taneously with glutamine. Glutamine oxidation was suppressed by amino- oxyacetate in both the presence and absence of exogenous glucose. In p articular, CO2 production from glutamine was reduced by 48 and 79% in the absence and presence of glucose, respectively; succinate CO2 ratio s (CO2 from [1,4-C-14]-succinate/[2,3-C-14]-succinate, unlabeled subst rate as specified) were reduced 59 and 71%, respectively, and the prob ability was doubled that glutamine carbon, which enters the TCA cycle, would complete a full turn of the cycle. These experiments confirmed earlier findings that glutamine carbon entering the TCA cycle is nor e ntirely oxidized and showed that processes of transamination are essen tial for high rates of glutamine entry into the TCA cycle. Transaminat ion appears also to be essential for efflux of intermediates from the TCA cycle and the synthesis of new compounds. Thus, transamination pro cesses apparently facilitate the incomplete oxidation of glutamine in intestinal cells. These studies showed also that carbon that leaves th e cycle re-enters predominantly via pyruvate dehydrogenase, rather tha n via pyruvate carboxylase, along the length of the small intestine.