Transamination processes promote incomplete glutamine oxidation in small intestine epithelial cells
1995
Kight, C.E. | Fleming, S.E.
The aim of the present study was to examine the influence of glucose on glutamine metabolism by intestinal epithelial cells. Cells were isolated from the proximal, mid, and distal small intestine of male, fed rats. The oxidation of [U14-C]glutamine was greatest in the proximal small intestine, and the stimulatory effect of glucose on glutamine oxidation was most pronounced in this segment also. Amino-oxyacetate, an aminotransferase inhibitor, did not influence the oxidation of glucose when present alone, but increased glucose oxidation when present simultaneously with glutamine. Glutamine oxidation was suppressed by amino-oxyacetate in both the presence and absence of exogenous glucose. In particular, CO2 production from glutamine was reduced by 48 and 79% in the absence and presence of glucose, respectively; succinate CO2 ratios (CO2 from [1,4-14C]-succinate/[2,3-14C]succinate, unlabeled substrate as specified) were reduced 59 and 71%, respectively, and the probability 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 not entirely oxidized and showed that processes of transamination are essential for high rates of glutamine entry into the TCA cycle. Transamination appears also to be essential for efflux of intermediates from the TCA cycle and the synthesis of new compounds. Thus, transamination processes apparently facilitate the incomplete oxidation of glutamine in intestinal cells. These studies showed also that carbon that leaves the cycle re-enters predominantly via pyruvate dehydrogenase, rather than via pyruvate carboxylase, along the length of the small intestine.
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