Uric acid lithiasis associated with altered kinetics of hypoxanthine-guanine phosphoribosyltranferase.

1. A patient is described who had uric acid calculi which obstructed both kidneys. Serum uric acid was 34 mg/100 ml upon admission to hospital, and evidence of precipitation of uric acid in joints was obtained. 2. Total activity of hypoxanthine-guanine phosphoribosyltransferase in erythrocytes lysates from this patient was 44% of normal. Kinetic studies revealed that the apparent Michaelis constant of this enzyme for phosphoribosyl pyrophosphate was elevated 15-fold, while these values for hypoxanthine and guanine were in the normal range.