THE BIOCHEMICAL CONVERSION OF 2-HYDROXY-4-METHYLTHIOBUTYRIC ACID INTO METHIONINE BY THE RAT IN VITRO

1. The conversion of 2-hydroxy-4-methylthiobarbituric acid into methionine requires a flavine coenzyme, which can be partially replaced by NAD or NADP, and glutamine, which can be partially replaced by asparagine. The system also requires aerobic conditions. 2. There does not appear to be a requirement for a metal ion: Mn(2+) is slightly inhibitory and Cu(2+) is strongly inhibitory. 3. Of the kidney, liver, brain, small intestine and muscle, the kidney possesses the greatest conversion activity/g. of tissue, but on a total organ basis the liver is the more important organ. Within the liver cells most of the activity is present in the supernatant fraction.

COBALT COMPOUNDS AS ANTIDOTES FOR HYDROCYANIC ACID

The antidotal potency of a cobalt salt (acetate), of dicobalt edetate, of hydroxocobalamin and of cobinamide against hydrocyanic acid was examined mainly on mice and rabbits. All the compounds were active antidotes for up to twice the LD50; under some conditions for larger doses. The most successful was cobalt acetate for rabbits (5xLD50), which was effective at a molar cyanide/cobalt (CN/Co) ratio of 5, but had as a side-effect intense purgation. Hydroxocobalamin was irregular in action, but on the whole was most effective for mice (4.5xLD50 at a molar ratio of 1), and had no apparent side effects. Dicobalt edetate, at molar ratios of up to 2, was more effective for rabbits (3xLD50) than for mice (2xLD50), but had fewer side effects than cobalt acetate. The effect of thiosulphate was to augment the efficacy of dicobalt edetate and, in mice, that of hydroxocobalamin; but, apparently, in rabbits, to reduce that of hydroxocobalamin. Cobinamide, at a molar ratio of 1, was slightly more effective than hydroxocobalamin on rabbits and also less irregular in its action. Cobalt acetate by mouth was effective against orally administered hydrocyanic acid. The oxygen uptake of the body, reduced by cyanide, is rapidly reinstated when one of the cobalt antidotes has been successfully administered.

CHARACTERIZATION OF LEPTOSPIRAL LIPASE

Patel, Virendra (University of Missouri, Columbia), Herbert S. Goldberg, and Donald Blenden. Characterization of leptospiral lipase. J. Bacteriol. 88:877-884. 1964.-A technique for leptospiral lipase extraction which yielded a highly active, stable, and concentrated lipase preparation was developed. The chief characteristics of leptospiral lipase were determined and are summarized below. Leptospiral lipase was soluble in water and stable in both the dry state and in aqueous solution. Tributyrin was found to be the substrate upon which the enzyme was most active. With this substrate, leptospiral lipase was found to display optimal activity at pH 7 and at 30 C. The Michaelis constant of leptospiral lipase with tributyrin substrate was determined to be 4.76 x 10(-2)m. The enzyme was not inhibited by low concentrations of mercury, iron, cobalt, or copper or by -SH blocking agents. Bile and calcium chloride in low concentrations were able to increase lipase activity at alkaline pH. The isoelectric point of leptospiral lipase was determined to be in the range of pH 5.2 to 5.4.

HAEM SYNTHASE AND COBALT PORPHYRIN SYNTHASE IN VARIOUS MICRO-ORGANISMS

1. The preparation of a crude extract of Clostridium tetanomorphum containing cobalt porphyrin synthase but little haem-synthase activity is described. 2. The properties of cobalt porphyrin synthase in the clostridial extracts is compared with the properties of a haem synthase present in crude extracts of the yeast Torulopsis utilis. 3. Cobalt porphyrin synthase in extracts of C. tetanomorphum inserts Co(2+) ions into the following dicarboxylic porphyrins in descending order of rate of insertion: meso-, deutero- and proto-porphyrins. Esterification renders meso- and deutero-porphyrins inactive as substrates. Neither the tetracarboxylic (coproporphyrin III) nor the octacarboxylic (uroporphyrin III) compounds are converted into cobalt porphyrins by the extract, but the non-enzymic incorporation of Co(2+) ions into these two porphyrins is rapid. These extracts are unable to insert Mn(2+), Zn(2+), Mg(2+) or Cu(2+) ions into mesoporphyrin. 4. Crude extracts of T. utilis readily insert both Co(2+) and Fe(2+) ions into deutero-, meso, and proto-porphyrins. Unlike the extracts of C. tetanomorphum, these preparations catalyse the insertion of Co(2+) ions into deuteroporphyrin more rapidly than into mesoporphyrin. This parallels the formation of haems by the T. utilis extract. 5. Cobalt porphyrin synthase is present in the particulate fraction of the extracts of C. tetanomorphum but requires a heat-stable factor present in the soluble fraction. This soluble factor can be replaced by GSH. 6. Cobalt porphyrin synthase in the clostridial extract is inhibited by iodoacetamide and to a smaller extent by p-chloromercuribenzoate and N-ethylmaleimide. The haem synthases of T. utilis and Micrococcus denitrificans are also inhibited by various thiol reagents.

THE METAL ION ACTIVATION OF THE ALKALINE BETA-GLYCEROPHOSPHATASE OF RABBIT SMALL INTESTINE

1. A fraction of intestinal epithelial cells from rabbit small intestine that contained nuclei and microvillus membranes served as a source of alkaline-beta-glycerophosphatase activity. 2. The greater part of the enzyme activity could be released from the subcellular particles by disintegration of the latter, followed by centrifugation at 40000g and butanol extraction of the resulting sediment. 3. Further purification of the enzyme was achieved by diethylaminoethylcellulose chromatography and by gel filtration. 4. Dialysis of the purified enzyme preparations against EDTA gave an essentially inactive enzyme. High activity could be restored by adding Zn(2+)+Mg(2+), Zn(2+)+Co(2+), Mg(2+)+Co(2+) or Co(2+) alone to these inactive preparations. Neither Zn(2+) nor Mg(2+) added singly to the assay system restored more than a small part of the enzyme activity. 5. The optimum Zn(2+) concentration was about 0.2-1m-equiv./l., whereas Mg(2+) and Co(2+) had optimum concentrations about 30-60m-equiv./l. 6. If added in excess of the optimum concentration, Zn(2+) strongly inhibited the enzyme under all conditions tested. 7. In the presence of an optimum concentration of Co(2+) (33m-equiv./l.) in tris buffer at the optimum pH (8.8 at 37 degrees ), K(m) for the beta-glycerophosphatase was 0.3mm.

THE METABOLISM OF GALACTARATE, D-GLUCARATE AND VARIOUS PENTOSES BY SPECIES OF PSEUDOMONAS

1. When NAD(+) was present, cell extracts of Pseudomonas (A) grown with d-glucarate or galactarate converted 1mol. of either substrate into 1mol. each of 2-oxoglutarate and carbon dioxide; 70-80% of the gas originated from C-1 of the hexarate. 2. The enzyme system that liberated carbon dioxide from galactarate was inactive in air and was stabilized by galactarate or Fe(2+) ions; the system that acted on d-glucarate was more stable and was stimulated by Mg(2+) ions. 3. When NAD(+) was not added, 2-oxoglutarate semialdehyde accumulated from either substrate. This compound was isolated as its bis-2,4-dinitrophenylhydrazone, and several properties of the derivative were compared with those of the chemically synthesized material. Methods were developed for the determination of 2-oxoglutarate semialdehyde. 4. Synthetic 2-oxoglutarate semialdehyde was converted into 2-oxoglutarate by an enzyme that required NAD(+); the reaction rate with NADP(+) was about one-sixth of that with NAD(+). 5. For extracts of Pseudomonas (A) grown with d-glucarate or galactarate, or for those of Pseudomonas fragi grown with l-arabinose or d-xylose, specific activities of 2-oxoglutarate semialdehyde-NAD oxidoreductase were much higher than for extracts of the organisms grown with (+)-tartrate and d-glucose respectively. 6. Extracts of Pseudomonas fragi grown with l-arabinose or d-xylose converted l-arabonate or d-xylonate into 2-oxoglutarate when NAD(+) was added to reaction mixtures and into 2-oxoglutarate semialdehyde when NAD(+) was omitted.