[Testing the activity of enzymes responsible for biosynthesis of purine nucleotides AIR-carboxylase and SAICAR-synthetase in human cell extracts].

Activities of AIR-carboxylase (ES 4.1.1.21) and SAICAR-synthetase (EC 6.3.2.6) were found in lysates of human erythrocytes, thrombocytes and leukocytes and in homogenate of the stomach biopsy sample. However, these activities were absent in blood plasma and bile. The human erythrocyte enzyme preparation, which had both activities, was isolated and purified about 200 times. The copurification of both activities and properties of the enzyme preparation suggest that two consecutive reactions of purine biosynthesis de novo (from AIR to SAICAR) in human cells are catalyzed by one bifunctional enzyme which is probably encoded by one gene.