An interaction between S-adenosyl-L-methionine and pyridoxal 5'-phosphate, and its effect on Saccharomyces cerevisiae

Cystathionine-synthase-deficient patients do not use the transamination pathway of methionine to reduce hypermethioninemia and homocystinemia

Methionine is supposed to be degraded via two known routes, the transsulfuration and the transamination pathways. In particular, patients with hypermethioninemia, due to a defect in the transsulfuration pathway, may catabolize significant amounts of methionine via the transamination pathway. In this study the relative amount of methionine degraded via the transamination pathway in 17 patients with homozygous homocystinuria, due to cystathionine synthase deficiency, was compared with 23 normal subjects, and with a patient with hypermethioninemia due to a deficiency in methionine adenosyltransferase. The homocystinuric patients and the normal subjects were studied in the fasting state as well as after methionine loading (0.1 g/kg body weight). It is concluded that in cystathionine synthase deficient patients, the transamination pathway is not quantitatively important in methionine degradation despite elevated methionine levels. This is in contrast to the patient with methionine adenosyltransferase deficiency, who catabolizes at least 20% of his dietary methionine via the transamination pathway.

Effect of vanadate and pyridoxal phosphate on S-adenosylmethionine

Vanadate in the presence of pyridoxal phosphate promotes the decarboxylation of S-adenosylmethionine. Pyridoxal has a lower effect; pyridoxine none. The rate of decarboxylation depends on pyridoxal phosphate and vanadate concentration. Vanadate as low as 10(-7) M gives significant decarboxylation. The reaction seems to occur through the formation of a Schiff base. The spectral shift elicited by S-adenosylmethionine on pyridoxal phosphate due to the presence of the sulfonium function is influenced by vanadate. Orthovanadate is a little less effective then metavanadate; vanadyl sulfate is even less efficient, and the effect of Cu2+ at the same concentration is still lower. Bleomycin partially prevents the vanadium effect. In vivo, vanadate promotes a marked increase in chicken liver S-adenosylmethionine and S-adenosylhomocysteine concentration, whereas the polyamine concentration is unaffected.

Initiation of meiosis and sporulation of Saccharomyces cerevisiae by sulfur or guanine deprivation

Homothallic Saccharomyces cerevisiae, growing exponentially in a synthetic acetate medium, could be initiated to undergo meiosis and subsequent sporulation by removal of sulfur from the medium or by partial purine deprivation of purine auxotrophs or, most efficiently, by guanine deprivation of a guanine auxotroph. In contrast, partial uracil deprivation of uracil auxotrophs did not cause sporulation. Under any of the above and other sporulation conditions, the intracellular concentrations of GTP and, usually at some time later, S-adenosylmethionine (SAM) decreased; the concentrations of the other nucleoside triphosphates decreased under some but increased under other sporulation conditions. The addition of 1 mM methionine or, more effectively, of SAM or the combination of adenine plus methionine greatly increased the intracellular concentration of SAM and reduced or prevented sporulation, even when GTP decreased. However, differentiation can be inhibited by an excess of many metabolites which do not specifically control the initiation process; in particular, SAM is known to inhibit yeast metabolism (e.g., transamination). Therefore, we cannot yet decide whether the deficiency of GTP or SAM (or related compounds) serves as a signal for the initiation of meiosis/sporulation.

In vivo formation of histamine phosphopyridoxal cyclic compounds

A possibility of in vivo formation of cyclic compounds between histamine (Hi) given i.p. and endogenous pyridoxal (PL) or pyridoxal 5'-phosphate (PLP) has been studied. Cyclic compounds of Hi with PL or PLP were found in all tissues examined. Although an increase in Hi levels in tissues enhances the formation of cyclic compounds, no simple relationship between the rate of formation and Hi concentration has been observed. The reaction seems to be limited by endogenous PLP. The cyclic products Hi-PL and Hi-PLP were discovered in urine. It is suggested that the process of cyclic compound formation may reduce PLP resources, resulting in a modification of PLP-enzyme activities.

Phosphopyridoxal cyclic compounds with histamine and histidine. 6: The formation of phosphopyridoxal cyclic compounds with histamine and histidine in the presence of biological material

We have studied the dynamics of cyclic compound formation between histamine or histidine and pyridoxal 5'-phosphate (Hi-PLP or His-PLP) in incubates of rat gastric mucosa histidine decarboxylase (HD), rat intestinal diamine oxidase (DAO) or homogenates of either rat liver, intestine or gastric mucosa. For gastric mucosa HD, liver and gastric mucosa homogenates, the rate of cyclization was slightly decreased; however, the rate was significantly inhibited with intestinal DAO or intestinal homogenate. Binding of PLP by tissue components was measured; free PLP was bound abundantly by rat intestinal DAO and by rat intestinal homogenate. A possible mechanism by which intestinal tissues inhibit cyclic compound formation is discussed.

Phosphopyridoxal complexes with histamine and histidine. (5) The kinetics of cyclic compound formation between histamine and pyridoxal-5'-phosphate in the presence of pig kidney diamine oxidase and rat intestinal histaminase

Pig kidney diamine oxidase (DAO) and rat intestinal histaminase (Hi-ase) activities are inhibited in vitro by high concentrations of both a substrate (histamine) and a coenzyme (pyridoxal-5'-phosphate). This inhibition may be at least partially associated with the formation of a cyclic compound between histamine (Hi) and pyridoxal-5'-phosphate (PLP). The dynamics of this cyclic compound formation in the presence of both enzymes has been examined. In an incubation mixture containing partially purified pig kidney DAO, the rate of cyclization decreased slightly as compared with a buffer. On the contrary, in the presence of crude rat intestinal histaminase, the rate of cyclization was inhibited significantly; this inhibition was proportional to the amount of enzyme preparation present in the incubation mixture. The possible mechanism of the influence of enzyme protein on the rate of cyclic compound formation, and its possible biological significance, are discussed.

Mechanism of inhibition of Chromatium D growth by L-methionine. Regulation of L-threonine biosynthesis by the intracellular level of S-adenosylmethionine

(1) An unusual accumulation of S-adenosyl-L-methionine in Chromatium D was associated with a marked growth inhibition by L-methionine. The inhibition was overcome by L-isoleucine, L-leucine, L-phyenylalanine, L-threonine, L-valine and putrescien. Based on their effects, these compounds are classified into 3 types. (2) L-Isoleucine, L-leucine, L-phyenylalanine and L-valine (Type I) inhibited the L-methionine uptake and consequently prevented the bacterium from the unusual accumulation of S-adenosyl-L-methionine even in the presence of L-methionine in the medium. Putrescine (Type II) stimulated the consumption of S-adenosyl-L-methionine, but did not influence the L-methionine uptake. Hence, the effect of putrescine would be explained by the action to diminish the intracellular level of S-adenosyl-L-methionine. L-Threonine (Type III) neither inhibited the L-methionine uptake nor affected the content of S-adenoxyl-L-methionine due to the addition of L-methionine. (3) The specific activity of homoserine kinase (EC 2.7.1.39) was greatly lowered by the addition of L-methionine under conditions in which Chromatium D unusually accumulates S-adenoxyl-L-methionine. Homoserine dehydrogenase (EC 1.1.1.3) activity was inhbitied by S-adenosyl-L-methionine (50% inhibition index, 3.5 mM). These facts strongly suggest that the growth inhibition by L-methionine is associated with the L-threonine deficiency caused by the unusual accumulation of S-adenosyl-L-methionine.

Phosphopyridoxal complexes with histamine and histidine. (4) The kinetics of complex formation between histidine and pyridoxal 5' -phosphate in the presence of bacterial histidine decarboxylase

The dynamics of the complex formation between pyridoxal 5'-phosphate (PLP) and histidine in the presence of bacterial histidine decarboxylase was examined. Since PLP is able to form a cyclic product with histidine and histamine, the possibility of complex formation between PLP and histamine formed during a decarboxylation reaction was examined too. It was found that the cyclization reaction between PLP and histidine is equimolecular and the rate of cyclic product formation is not significantly influenced by the presence of enzyme. In the presence of bacterial histidine decarboxylase both the cyclization reaction and cyclic product formation were observed. Predominance of histamine or cyclic product formation was dependent on pH and substrate concentration. In the presence of histidine and enzymatic protein, histamine formed during the decarboxylation reaction was unable to form a cyclic product with PLP.

Phosphopyridoxal complexes with histamine and histidine. (2) The influence of presumed complex on histidine decarboxylase activity in rat gastric mucosa

It was found that in vitro, histidine and histamine form a complex compound with pyridoxal-5'-phosphate (PLP). The purpose of the present experiments was to find whether formation of this complex can influence histidine decarboxylase activity. It was found that excess PLP inhibits rat's gastric mucosa histidine decarboxylase activity in vitro. The inhibitory action of PLP depends on the histidine concentration and is independent on the amount of crude enzyme preparation. The histidine-PLP complex did not influence enzyme activity. The possible mechanisms of the inhibitory action of PLP on histidine decarboxylase activity are discussed.

Phosphopyridoxal complexes with histamine and histidine. (1) The kinetics of complex formation between pyridoxal 5'-phosphate and histamine

Amines and amino acids are able to form cyclic compounds with pyridoxal 5'-phosphate (PLP). The quantitative relationship between histamine and PLP in the cyclization reaction were examined. It was found that one mole of amine reacts with one mole of coenzyme. The velocity of complex formation increased with an excess of either histamine or PLP, without any change in molar ratios. The formation of cyclic compound was confirmed by the use of isotopic method. The separation of cyclic compound from histamine, but not from PLP, was achieved by paper chromatography.

Phosphopyridoxal complexes with histamine and histidine. (3) The influence of presumed complex on activity of rat intestinal histaminase

Histamine in high concentration inhibits the rat intestinal histaminase (diamine oxidase E.C. 1.4.3.6.). The apparent Km is approximately 4.2 X 10(-5) M. This inhibition can be reversed by an addition of PLP. It was also found that excess of PLP inhibits enzyme activity. It is competitive inhibition. Histamine and other amines which were associated with enzyme inhibition form spectrophotometricaly demonstrable complex with PLP. The possible mechanism of the inhibitory action of PLP and complex with histamine and other amines on rat intestinal histaminase activity are discussed.