In vitro metabolism of C-14-labeled amino acids by sheep kidney cortex and medulla

Abstract

Sheep kidney cortex slices incorporated significant amount of C14 into C14O2 when incubated with l-glutamic acid-U-C14 or with l-glutamine-U-C . Much smaller incorporation of C14 into C14O2 was observed when cortex slices were incubated with l-leucine-U-C14 and with 1-lysine-U-C14. Sheep kidney cortex slices did not form C14O2 when incubated with l-phenylalanine-U-Cl4. Medullary slices incorporated small quantities of C14 into C14CO2 when incubated with l-glutamine-U-C^4 and with l-leucine-U-C14. C14 incorporation into protein was less than 0. 4% of added C14 in all experiments. The results of kinetic studies were compatible with the presence of active transport systems in cortex slices for l-glutamine, 1-glutamic acid, and l-lysine. The concentrations of l-leucine and l-phenylalanine used may have exceeded the capacity of limited transport processes for these amino acids. No active transport processes for amino acids were demonstrable in medullary cells although considerable uptake of glutamine, apparently by diffusion, was observed. The distribution of inulin-carboxyl-C14 indicated an inulin space in cortex slices of 27. 4% of final tissue wet weight and in medullary slices of 44. 8% of final tissue wet weight.