A comparative study of the renal glutaminase response to acidosis

The rates of ammonia excretion and the activities of renal glutaminase were measured in the rat, dog, guinea pig and chicken. The rate of ammonia excretion and the activity of renal glutaminase were less in guinea pig than in the other species. Renal glutaminase from all four species was activated by phosphate, but the degree of activation varied between species. Many organic acids activated renal glutaminase in the rat, dog and chicken, but these compounds were without affect or decreased glutaminase activity in the guinea pig. The optimal pH for renal glutaminase was 7.4, 8.0 and 8.8 for the guinea pig, rat and dog respectively, while in the chicken a plateau was reached between pH 7.5 and 9.5. The activation of renal glutaminase by phosphate in the chicken was greater at sub-optimal pH values than in the plateau region. In the absence of an activator acidosis did not affect glutaminase activity in any species. When phosphate was present in the incubation medium acidosis increased glutaminase activity in the rat and chicken, but did not alter enzyme activity in the guinea pig or dog. Acidosis did not affect the optimal pH or the shape of the activity versus pH curve in any of the species.