New procedures for purification of L-asparaginase with high yield from Escherichia coli

l-Asparaginase is now known to be a potent antineoplastic agent in animals and has given complete remission in some human leukemias. Extensive clinical trials of this enzyme, however, were not possible in the past because of inadequate production of this substance. We have developed practical procedures for producing l-asparaginase in yields of sufficient quantity and purity for more extensive clinical evaluation. The nutritional requirements for optimal production of biologically active l-asparaginase by a strain of Escherichia coli have been ascertained. The highest yields of enzyme were obtained when cells were grown aerobically in a corn steep medium. Good enzyme production was associated with media containing l-glutamic acid, l-methionine, and lactic acid. The addition of glucose to the medium, however, resulted in depressed production of l-asparaginase. Sodium ion appeared to suppress l-asparaginase production. With the procedure described for isolation of biologically active l-asparaginase from E. coli, stable l-asparaginase preparations with a specific activity of 620 IU per mg of protein (1,240-fold purification with 40% total recovery) were obtained.     

A comparison of the effects of NN′-dicyclohexylcarbodi-imide, oligomycin A and aurovertin on energy-linked reactions in mitochondria and submitochondrial particles

1. The effects of dicyclohexylcarbodi-imide, oligomycin A and aurovertin on enzyme systems related to respiratory-chain phosphorylation were compared. Dicyclohexylcarbodi-imide and oligomycin A have very similar functional effects, giving 50% inhibition of ATP-utilizing and ATP-generating systems at concentrations below 0.8nmole/mg. of submitochondrial-particle protein. Aurovertin is a more potent inhibitor of ATP synthesis, giving 50% inhibition at 0.2nmole/mg. of protein. However, aurovertin is a less potent inhibitor of ATP-utilizing systems: the ATP-driven energy-linked nicotinamide nucleotide transhydrogenase is 50% inhibited at 3.0nmoles/mg. of protein and the ATP-driven reduction of NAD(+) by succinate is 50% inhibited at 0.95nmole/mg. of protein. 2. With EDTA-particles (prepared by subjecting mitochondria to ultrasonic radiation at pH9 in the presence of 2mm-EDTA) the maximum stimulation of the ATP-driven partial reactions is effected by similar concentrations of oligomycin A and dicylcohexylcarbodi-imide, but the latter is less effective. The stimulatory effects of suboptimum concentrations of dicyclohexylcarbodi-imide and oligomycin A are additive. Aurovertin does not stimulate these reactions or interfere with the stimulation by the other inhibitors. 3. Dicyclohexylcarbodi-imide and oligomycin A stimulate the aerobic energy-linked nicotinamide nucleotide transhydrogenase of EDTA-particles, but the optimum concentration is higher than that required for the ATP-driven partial reactions. Aurovertin has no effect on this reaction. 4. The site of action of dicyclohexylcarbodi-imide is in CF(0), the mitochondrial fraction that confers oligomycin sensitivity on F(1) mitochondrial adenosine triphosphatase.     

The purine and pyrimidine metabolism of Tetrahymena pyriformis

The metabolism of purines and pyrimidines by the ciliated protozoan Tetrahymena was investigated with the use of enzymatic assays and radioactive tracers. A survey of enzymes involved in purine metabolism revealed that the activities of inosine and guanosine phosphorylase (purine nucleoside: orthophosphate ribosyltransferase, E.C. 2.4.2.1) were high, but adenosine phosphorylase activity could not be demonstrated. The apparent K_m for guanosine in the system catalyzing its phosphorolysis was 4.1 ± 0.6 × 10^?3 M. Pyrophosphorylase activities for IMP and GMP (GMP: pyrophosphate phosphoribosyltransferase, E.C. 2.4.2.8), AMP (AMP: pyrophosphate phosphoribosyltransferase, E.C. 2.4.2.7), and 6-mercaptopurine ribonucleotide were also found in this organism; but a number of purine and pyrimidine analogs did not function as substrates for these enzymes. The metabolism of labeled guanine and hypoxanthine by intact cells was consistent with the presence of the phosphorylases and pyrophosphorylases of purine metabolism found by enzymatic studies. Assays for adenosine kinase (ATP: adenosine 5'-phosphotransferase, E.C. 2.7.1.20) inosine kinase, guanosine kinase, xanthine oxidase (xanthine: O₂ oxidoreductase, E.C. 1.2.3.2), and GMP reductase (reduced-NADP: GMP oxidoreductase [deaminating], E.C. 1.6.6.8) were all negative. In pyrimidine metabolism, cytidine-deoxycytidine deaminase (cytidine aminohydrolase, E.C. 3.5.4.5), thymidine phosphorylase (thymidine: orthophosphate ribosyltransferase, E.C. 2.4.2.4), and uridine-deoxyuridine phosphorylase (uridine: orthophosphate ribosyltransferase, E.C. 2.4.2.3) were active; but cytidine kinase, uridine kinase (ATP: uridine 5'-phosphotransferase, E.C. 2.7.1.48), and CMP pyrophosphorylase could not be demonstrated.     

Genetic Basis of Colicin E Susceptibility in Escherichia coli I. Isolation and Properties of Refractory Mutants and the Preliminary Mapping of Their Mutations

Colicin E-resistant mutants were isolated in Escherichia coli K-12 which, although still apparently possessing the E receptor and adsorbing colicin, were nevertheless insensitive (refractory) to its effect. Eight phenotypic groups were obtained, but some mutants from three of these groups were all shown to map at gal, whereas a second refractory locus, giving resistance to E1 alone, mapped close to thy. It is suggested that the successful fixation of any of the three distinct colicins of group E may involve a dual role for the cell surface "receptor," the first for the binding of the protein and the second for the correct orientation of the bound molecule relative to the cytoplasmic membrane. The majority of the refractory mutants isolated may derive from changes in components concerned with the second of these receptor functions. Two groups of mutants, however, refractory to only E1 or E2, probably reflect changes in the intracellular transmission systems which specifically mediate the effects of these two colicins, the changes not allowing transmission through the cytoplasmic membrane to the respective targets of the colicins. The E1 adsorption site was shown to be distinct from that for E2 and E3, indicating an early separation of the colicin E transmission systems.