Abstract
Unilateral nephrectomy leads to the compensatory growth of the remaining kidney and to enhanced activity of biochemical parameters associated with cellular growth. Within hours there is increased uptake of radiolabeled nucleotides and synthesis of RNA and protein with stimulation of DNA synthesis occurring somewhat later (1—7). Induction of certain enzymes involved in DNA synthesis is maximal in 24—48 hr (8). This is a report of renal aspartate carbamyltransferase (ACTase) in the uninephrectomized rat (9). ACTase (EC2.1.3.2) catalyzes the first step unique to pyrimidine biosynthesis, the carbamylation of aspartate by carbamyl phosphate (10). The product, carbamyl aspartate, is a precursor of orotic acid; therefore, of the pyrimidines and ultimately of RNA and DNA. In bacteria the control of ACTase by nucleotides is a classical example of biochemical feedback (11). ACTase is particularly active in plant and animal tissues which are either growing rapidly or undergoing constant renewal, e.g., apical meristems, plant root tips, regenerating liver, fetal tissues, intestinal mucosa, and testis. Unusually high ACTase activities occur in certain tumors (10).
Materials and Methods. Female Wistar rats, 150—200 g, were kept in groups of four or five in stainless-steel cages containing corn cob bedding. They had free access to Purina Laboratory Chow and water. Nephrectomies were performed under ether anesthesia. After ligating its blood vessel connections, the right and larger kidney was removed through dorsal, subcostal skin, and muscle incisions. In some experiments ACTase activity of this kidney was assayed. Control animals were sham operated. At various times after uninephrectomy all rats were killed by decapitation. After perfusion with isotonic NaCl via the abdominal aorta the remaining kidney was removed, blotted, and weighed. A 1:15 (w/v) homogenate in ice-cold isotonic KCl was prepared and centrifuged (29,000g) for 1 hr at 4†.
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