Proline biosynthesis by cell-free extracts of Escherichia coli and potential errors arising from the use of a bioradiological assay procedure

Endogenous synthesis of arginine plays an important role in maintaining arginine homeostasis in postweaning growing pigs

This study was conducted to determine whether endogenous synthesis of arginine plays a role in regulating arginine homeostasis in postweaning pigs. Pigs were fed a sorghum-based diet containing 0. 98% arginine and were used for studies at 75 d of age (28.4 kg body weight). Mitochondria were prepared from the jejunum and other major tissues for measuring the activities of Delta1-pyrroline-5-carboxylate (P5C) synthase and proline oxidase (enzymes catalyzing P5C synthesis from glutamate and proline, respectively) and of ornithine aminotransferase (OAT) (the enzyme catalyzing the interconversion of P5C into ornithine). For metabolic studies, jejunal enterocytes were incubated at 37 degrees C for 30 min in Krebs-Henseleit bicarbonate buffer containing 2 mmol/L L-glutamine, 2 mmol/L L-[U-14C]proline, and 0-200 micromol/L gabaculine (an inhibitor of OAT). The activities of P5C synthase, proline oxidase and OAT were greatest in enterocytes among all of the tissues studied. Incubation of enterocytes with gabaculine resulted in decreases (P < 0.05) in the synthesis of ornithine and citrulline from glutamine and proline. When gabaculine was orally administered to pigs (0.83 mg/kg body weight) to inhibit intestinal synthesis of citrulline from glutamine and proline, plasma concentrations of citrulline (-26%) and arginine (-22%) decreased (P < 0.05), whereas those of alanine (+21%), ornithine (+17%), proline (+107%), taurine (+56%) and branched-chain amino acids (+21-40%) increased (P < 0.05). On the basis of dietary arginine intake and estimated arginine utilization, the endogenous synthesis of arginine in the 28-kg pig provided >/=50.2% of total daily arginine requirement. Taken together, our results suggest an important role for endogenous synthesis of arginine in regulating arginine homeostasis in postweaning growing pigs, as previously shown in neonatal pigs.

Gene-enzyme relationships in the proline biosynthetic pathway of Saccharomyces cerevisiae

The PRO1, PRO2, and PRO3 genes were isolated by functional complementation of pro1, pro2, and pro3 (proline-requiring) strains of Saccharomyces cerevisiae. Independent clones with overlapping inserts were isolated from S. cerevisiae genomic libraries in YEp24 (2 microns) and YCp50 (CEN) plasmids. The identity of each gene was determined by gene disruption, and Southern hybridization and genetic analyses confirmed that the bona fide genes had been cloned. Plasmids containing each gene were introduced into known bacterial proline auxotrophs, and the ability to restore proline prototrophy was assessed. Interspecies complementation demonstrated that the S. cerevisiae PRO1 gene encoded gamma-glutamyl kinase, PRO2 encoded gamma-glutamyl phosphate reductase, and PRO3 encoded delta 1-pyrroline-5-carboxylate reductase. The presence of the PRO3 gene on a high-copy-number plasmid in S. cerevisiae caused a 20-fold overproduction of delta 1-pyrroline-5-carboxylate reductase. The PRO2 gene mapped on chromosome XV tightly linked to cdc66, and the PRO3 gene was located on the right arm of chromosome V between HIS1 and the centromere.

Proline biosynthesis in Escherichia coli. Purification and characterisation of glutamate-semialdehyde dehydrogenase

Glutamate-semialdehyde dehydrogenase, catalysing the reduction in vivo of gamma-glutamyl phosphate to glutamate 5-semialdehyde in the pathway of proline biosynthesis in Escherichia coli, has been purified to homogeneity. High initial levels of the enzyme were achieved by using a multicopy ColEl-pro A, B hybrid plasmid. The protein has a molecular weight of 1.89 X 10(5) and consists of four identical subunits of molecular weight 4.7 X 10(4) each. The pH optimum is 7.0 and the protein is stable for at least 10 min between pH 6.0-9.0 and for long periods at pH 7.0 It is rapidly inactivated at temperatures greater than 50 degrees C. The enzyme is very sensitive to inhibition by p-chloro-mercuribenzoate, copper and nickel ions.

The enzymes of proline biosynthesis in Escherichia coli. Their molecular weights and the problem of enzyme aggregation

1. By using Bio-Gel A1.5M and Sephadex G-150 columns, crude cell-free extracts of Escherichia coli were fractionated to demonstrate the existence of a proline-biosynthetic aggregate. 2. Sephadex G-150 resolves two glutamyl kinases that are inhibited by proline, with mol.wts. of 125000 and 38000, the reactions of which are Mg2+-dependent. The heavier species is more sensitive to inhibition by proline. 3. Gamma-Glutamyl phosphate reductase and 1-pyrroline-5-carboxylate reductase (EC 1.5.1.2) have mol.wts. of approx. 125000 and 190000 respectively, the specific activity of the latter being 5 X 10(3)-fold greater than either of the other two biosynthetic enzymes or of the total pathway in vivo. 4. Bio-Gel A1.5M chromatography gave a single glutamyl kinase of mol.wt. 250000, and the possibility of this being a constituent of an enzyme complex is discussed.