Glutamate transprot in rat kidney mitochondria

The quantitative characteristics of [U-14C]glutamate transport were determined in rotenone-inhibited energized rat kidney mitochondria at pH 7.0 and 28 degrees C. Glutamate efflux was observed to be first order with respect to matrix glutamate with a rate constant of 0.457 min-1. Uptake kinetic studies indicated that the Km of external glutamate was 1.4 mM and the Vmax 3.2 nmol/mg X min. These kinetic values were found to be unchanged at pH 6.6 or in mitochondria obtained from kidneys of chronically acidotic rats. Parallel studies of glutamate deamination were performed in which mitochondria were incubated in state 3, state 4, and with carbonyl cyanide p-trifluoromethoxyphenylhydrazone, in the presence of malonate. The oxidative deamination of glutamate determined with 1 and 10 mM glutamate never exceeded the simultaneously measured rate of glutamate transport. No glutamate was detectable within the mitochondrial matrix under the conditions of these metabolic experiments. The studies indicate that the glutamate hydroxyl transporter is quite slow and rate limiting for the oxidative deamination of external glutamate in rat kidney mitochondria.