Jaakko Pispa

Ornithine decarboxylase from Escherichia coli: Stimulation of the enzyme activity by nucleotides

Abstract Ornithine decarboxylase (L-ornithine carboxy-lyase, EC 4.1.1.17) has been purified about 100-fold from cells of Escherichia coli F. The partially purified enzyme required pyridoxal phosphate and exhibited optimal activity at pH 8.5. The apparent Km value for L-ornithine was 2 mM. At every stage of purification ornithine decarboxylase activity was enhanced by nucleotides, especially by nucleotide triphosphates, guanosine and deoxyguanosine triphosphate showing the highest affinity for the enzyme. In the presence of saturating concentrations of guanosine triphosphate the Km value for L-ornithine was lowered to about one tenth of that in the absence of the nucleotide. The apparent Km for guanosine triphosphate as the activator of ornithine decarboxylase was below 0.001 mM.

The regulation of polyamine synthesis during the stringent control in Escherichia coli.

Summary The activity of ornithine decarboxylase (L-ornithine carboxy-lyase EC 4.1.1.17) and the accumulation of putrescine and spermidine were studied in Escherichia coli CP 78 (rel + ) and CP 79 (rel − ) strains during normal growth and amino acid starvation. Amino acid starvation decreased the activity of ornithine decarboxylase in crude lysates from the stringent strain. Similarly, the accumulation of polyamines was ceased by the deprival of the amino acids in the stringent strain but not in the relaxed one. Partially purified ornithine decarboxylase from Escherichia coli CP 78 was inhibited by guanosine 5′ diphosphate, 3′ diphosphate in a competitive manner with respect to guanosine triphosphate, the activator of the enzyme. These results suggest that the synthesis of polyamines in Escherichia coli CP 78 is regulated, at least partly by guanosine 5′ diphosphate, 3′diphosphate.

Inhibition of catalase in vitro and in vivo by 4-hydroxypyrazole, a metabolite of pyrazole

For many years it has been recognised that not all the properties of pyrazole are due to the molecule itself [l-4]. With the elucidation of the metabolism of pyrazole [S] it was appreciated that several metabolites could possess biological activity. In {6] an in vitro inhibition of catalase (EC 1 .l 1 .1.6) by 4-hydroxypyrazole (4-HP), one of the major metabolites of pyrazole was reported. This paper confirms the inhibition of catalase by 4-HP but also describes the importance of incubation time, a factor not studied earlier. We also describe the effects of 4-HP administration to mice on liver catalase activity.

On the induction of tyrosine aminotransferase in rat liver by α-methyl-p-tyrosine

Abstract Hepatic tyrosine aminotransferase ( l -tyrosine:2-oxoglutarate aminotransferase, EC 2.6.1.5) is known to be induced by α-methyl-p-tyrosine, a well-known catecholamine depletor, in both intact and adrenalectomized rats. The authors have studied this subject further and their results show that α-methyl-p-tyrosine does not influence the activity of tyrosine aminotransferase in the isolated, perfused liver and that hypophysectomy totally abolishes the induction of the enzyme by this agent. The involvement of hypophyseal hormones is discussed.

Inhibition of dopamine-β-hydroxylase by a metabolite of pyrazole, 4-hydroxypyrazole, in vitro

Pyrazole and its derivatives have been widely used in the studies on alcohol metabolism due to their ability to inhibit alcohol dehydrogenase. It was also observed that pyrazole treatment interfered with catecholamine metabolism in rat and mouse brain [ 1,2]. The decrease in concentration of brain noradrenaline (NA) was suggested to be caused by the inhibition of dopamine

Enhancement of biotinidase activity in mouse serum by inhibitors of methylation.

-hydroxylase (Df3H, EC 1.14.2.1) by pyrazole in vivo. This suggestion was later supported by the studies showing that subacute pyrazole treatment did, indeed, inhibit rat hypothalamic D/3H, in vivo, but not in vitro [3]. These results were partly confirmed by a report that single doses of pyrazole decreased [NA] in rat brain [4]. However, chronic treatment with lower doses increased [NA] in rat brain. No change in brain DflH activity was found. It has been reported that 4.hydroxypyrazole (4-HP) is a major metabolite of pyrazole in the rat [5]. The effect of 4-HP on the activity of DflH was studied [6]. They found that D/3H activity was strongly inhibited by 4-HP in vitro though the inhibition was reversible by dialysis. 4-HP inhibited DfiH activity in plasma and adrenals also in vivo but DflH activity in brain remained unchanged. Since our preliminary studies with 4-HP gave quite different results in vitro we decided to study this subject further [7]. We present results suggesting that the effect of 4-HP on DPH activity is mediated through the inhibition of stimulatory effect of catalase used in the assays in vitro.

Ontogeny of tyrosine aminotransferase in Xenopus laevis.

SummaryDL-ethionine increases the activity of liver biotinidase, an enzyme which hydrolyzes biotinylesters and biotinylpeptides. Chronic DL-ethionine feeding increases transiently the activity of biotinidase in mouse and rat liver, after which it remains elevated in the serum. In the present work we show that both isomers of DL-ethionine are equally good enhancers of the liver biotinidase, while, 3-ethylthiopropionate, the toxic metabolite of DL-ethionine, has no effect on the biotinidase activity of either liver or serum. We have also employed two different combinations of inhibitors of the hydrolytic pathway of SAH, a transmethylation product and potent inhibitor of methylation. It was found that these inhibitors (EHNA and Ara-A, 2-deoxycoformycin and adenosine) increase the activity of serum biotinidase as was the case with ethionine. Because SAH does not ethylate biomolecules, these changes in biotinidase activity, which can not be preveneted by adenine, biotin or lecithin are most probably related to the inhibition of methylation.

Effect of methylglyoxal bis(guanylhydrazone) on polyamine metabolism in normal and regenerating rat liver and rat thymus

Abstract The development of tyrosine aminotransferase (TAT) activity in Xenopus laevis embryos was studied. Undivided eggs can transaminate tyrosine to some extent. The enzyme activity increases after hatching on the third day of development. In the early stages of development, the transamination of tyrosine is due to aspartate aminotransferase (ASAT, EC 2.6.1.1), both isoenzymes of which are present in the undivided egg. No specific TAT (EC 2.6.1.5) can be detected until the age of about 1 day, at which time neurulation is complete and the rapid development of the foregut and visceral pouches and arches has begun. The appearance of the enzyme is immediately preceded by a steep increase in the concentration of free tyrosine. Tyrosine aminotransferase is known to be induced by its substrate in the adult liver, and a similar effect may operate in the embryo.