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T Toraya

Publications and source records attributed to T Toraya.

At least 55 records · Page 3Linked to original sources
PubMed1988

Roles of the beta-D-ribofuranose ring and the functional groups of the D-ribose moiety of adenosylcobalamin in the diol dehydratase reaction.

Four analogs of adenosylcobalamin (AdoCbl) modified in the D-ribose moiety of the Co beta ligand were synthesized, and their coenzymic properties were studied with diol dehydratase of Klebsiella pneumoniae ATCC 8724. 2'-Deoxyadenosylcobalamin (2'-dAdoCbl) and 3'-deoxyadenosylcobalamin (3'-dAdoCbl) were active as coenzyme. 2',3'-Secoadenosylcobalamin (2',3'-secoAdoCbl), an analog bearing the same functional groups as AdoCbl but nicked between the 2' and 3' positions in the ribose moiety, and its 2',3'-dialdehyde derivative (2',3'-secoAdoCbl dialdehyde) were totally inactive analogs of the coenzyme. It is therefore evident that the beta-D-ribofuranose ring itself, possibly its rigid structure, is essential and much more important than the functional groups of the ribose moiety for coenzymic function (relative importance: beta-D-ribofuranose ring much greater than 3'-OH greater than 2'-OH greater than ether group). With 2'-dAdoCbl and 3'-dAdoCbl as coenzymes, an absorption peak at 478 nm appeared during enzymatic reaction, suggesting homolysis of the C-Co bond to form cob(II)alamin as intermediate. In the absence of substrate, the complexes of the enzyme with these active analogs underwent rapid inactivation by oxygen. This suggests that their C-Co bond is activated even in the absence of substrate by binding to the apoprotein. No significant spectral changes were observed with 2',3'-secoAdoCbl upon binding to the apoenzyme. In contrast, spectroscopic observation indicates that 2'3'-secoAdoCbl dialdehyde, another inactive analog, underwent gradual and irreversible cleavage of the C-Co bond by interaction with the apodiol dehydratase, forming the enzyme-bound cob(II)alamin without intermediates.

Carbohydrate Conformation↗
PubMed1987

A factor potentiating serotonin in the induction of germinal vesicle breakdown in surf clam oocytes.

Simultaneous addition of an aliquot of body fluid obtained from the surf clam, Spisula solidissima, enhanced oocyte germinal vesicle breakdown induced with serotonin but not with KCl. When the body fluid and serotonin were added sequentially to the oocytes, potentiation did not occur. Body fluids of both males and females were effective at a 200-fold dilution. The factor is stable when treated with heat, acid, base, trypsin and pronase. It is hydrophobic and not dialyzable through tubing with a molecular weight cutoff of 1000 daltons. The factor is probably not a protein.

Animals↗
PubMed1987

Activation and cleavage of the carbon-cobalt bond of adeninylethylcobalamin by diol dehydrase.

Adeninylethylcobalamin (AdeEtCbl) underwent cleavage of the C-Co bond by interaction with apoprotein of diol dehydrase from Klebsiella pneumoniae ATCC 8724, although this analog was quite inactive as coenzyme. Spectroscopic observation indicates that AdeEtCbl was converted to the enzyme-bound hydroxocobalamin without intermediates. The conversion was stoichiometric (1:1) and obeyed the second-order reaction kinetics (k = 0.027 min-1 microM-1 at 37 degrees C) depending upon concentrations of apoprotein and AdeEtCbl. This suggests that the complex formation is the rate-determining step and that AdeEtCbl undergoes rapid C-Co bond cleavage once it binds to the apoenzyme. Substrates and oxygen did apparently not affect the rate of the C-Co bond cleavage. The experiments using [adenine-U-14C]AdeEtCbl and [1(3)-3H]glycerol demonstrated that 9-ethyladenine was the only product formed from the adeninylethyl group of AdeEtCbl during the conversion and that an additional hydrogen atom in the 9-ethyladenine is not derived from the substrate. 1H NMR measurement of the 9-ethyladenine formed enzymatically from AdeEtCbl and DL-1,2-[1,1,2-2H3]propanediol also led to the same conclusion. All of these results indicate that the C-Co bond of AdeEtCbl is activated by diol dehydrase and undergoes heterolysis forming Co(III) and a carbanion or a carbanion-like species, in clear contrast to the homolysis of the C-Co bond of adenosylcobalamin in the normal catalytic process. 9-Ethyladenine formed remained tightly associated with the enzyme. Longer chain homologs, i.e. adeninylpropylcobalamin, adeninylbutylcobalamin, and adeninylpentylcobalamin did not undergo such cleavage of the C-Co bond by diol dehydrase.

Adenine↗
PubMed1987

Re-investigation of the protein structure of coenzyme B12-dependent diol dehydrase.

We have purified diol dehydrase, an adenosylcobalamin-dependent enzyme, from Klebsiella pneumoniae by two different procedures to re-investigate its protein structure; one including its extraction with detergent from the membrane fraction, and the other consisting of only chromatographic separations of the soluble fraction. The enzyme preparations obtained by these two methods were different in the subunit structure, but both are identical in molecular weight, and in-enzymological and immunochemical properties. In addition, the enzyme preparation obtained from the membrane fraction dissociated reversibly into two dissimilar protein components (F and S) in the absence of substrate, as did the preparation from the soluble fraction. Although the subunit multiplicity of component S might be partly due to proteolytic cleavage during the enzyme purification as revealed by limited digestion with trypsin, component F is not a product of proteolytic cleavage of component S, but a primordial and essential constituent of the enzyme.

Cell Membrane↗
PubMed1986

The synthesis of adenine-modified analogs of adenosylcobalamin and their coenzymic function in the reaction catalyzed by diol dehydrase.

Five analogs of adenosylcobalamin modified in the adenine moiety of the Co beta ligand were synthesized and tested for coenzymic function with diol dehydrase of Klebsiella pneumoniae ATCC 8724. 1-Deaza and 3-deaza analogs of adenosylcobalamin were active as coenzyme, whereas 7-deaza and N6,N6-dimethyl derivatives and guanosylcobalamin did not show detectable coenzymic activity. 7-Deaza and N6,N6-dimethyl analogs acted as strong competitive inhibitors with respect to adenosylcobalamin. The formation of cob(II)alamin as intermediate in the catalytic reaction was spectroscopically observed with catalytically active complexes of the enzyme with 1-deaza and 3-deaza analogs in the presence of 1,2-propanediol, but not with complexes with the inactive analogs. Oxygen sensitivity of the enzyme-analog complexes suggests that the carbon-cobalt bond of 1-deaza and 3-deaza analogs becomes activated by the enzyme even in the absence of substrate. These results indicate that the importance of the nitrogen atoms in the adenine moiety of the coenzyme for manifestation of catalytic function and for activation of the carbon-cobalt bond decreases in the following order: N-7 greater than 6-NH2 greater than N-3 greater than N-1. The dissociation constant for 5'-deoxyadenosine determined by equilibrium dialysis at 37 degrees C was about 23 microM.

Adenine↗
PubMed1986

Identification of a dephosphorylated oxidation product of the molybdenum cofactor as 2-(1,2-dihydroxyethyl)thieno[3,2-g]pterin.

A new method was developed for the synthesis of 2-(1,2-dihydroxyethyl)thieno[3,2-g]pterin and related 2-substituted thienopterins. A dephosphorylated fluorescent oxidation product of the molybdenum cofactor isolated from xanthine oxidase (EC 1.2.3.2) was identified as 2-(1,2-dihydroxyethyl)thieno[3,2-g]pterin by comparison of electronic and fluorescence spectra and TLC behaviors with those of the synthetic compound.

Chromatography, Thin Layer↗
PubMed1985

The binding site for the adenosyl group of coenzyme B12 in diol dehydrase.

The binding of cob(II)alamin (CblII) and 5'-deoxyadenosine to diol dehydrase was studied spectroscopically and with [U-14C]5'-deoxyadenosine. CblII was bound to this enzyme forming a tight 1:1 complex which was resistant to oxidation by O2 even in the presence of CN-. An irreversible 1:1:1 ternary complex was formed between enzyme, CblII, and 5'-deoxyadenosine, when the enzyme was incubated first with the nucleoside and then with CblII. When this order of addition of the constituents was reversed, no 5'-deoxyadenosine was bound to the enzyme-CblII complex. Hydroxocobalamin could also bind to the enzyme together with the nucleoside, while other cob(III)alamins bearing a bulkier Co beta ligand displaced the nucleoside upon binding to the enzyme. The binding of [U-14C]5'-deoxyadenosine was strongly inhibited by unlabeled 5'-deoxy-ara-adenosine, 4',5'-anhydroadenosine, adenosine, adenine, and 5',8-cyclic adenosine, in this order, but not by 5'-deoxyuridine. These results constitute direct evidence for the presence of the binding site for the adenosyl group of adenosylcobalamin, which is spatially limited to and highly specific for adenine nucleosides. The binding of 5'-deoxyadenosine to the apoenzyme was reversible.

Binding Sites↗
PubMed1985

Functional role of cysteinyl residues in tryptophanase.

Holotryptophanase inactivated by oxidation of cysteinyl residues showed a different absorption spectrum from the native enzyme. At pH 8.0, the native enzyme preferentially existed as a 337-nm species (active form), whereas in the inactive enzyme a 420-nm species (inactive form) was dominant. During the reactivation of the enzyme by reduction with dithiothreitol, an increase at 337 nm and a decrease at 420 nm were observed with concomitant increase in enzymatic activity, which was accompanied by the appearance of two cysteinyl residues per monomer. Specific S-cyanylation of cysteinyl residues by nitrothiocyanobenzoic-acid-inactivated apotryptophanase with the modification of one cysteinyl residue per monomer, whereas holotryptophanase was highly resistant to inactivation with nitrothiocyanobenzoic acid. The essential role of the active-site-bound pyridoxal 5'-phosphate in protection against inactivation was confirmed by the agreement of the K1/2 (protection) of 5.0 microM for pyridoxal 5'-phosphate with Km of 2.0 microM in enzyme catalysis. The inactivation by nitrothiocyanobenzoic acid caused a similar shift in the equilibrium between the 337-nm species and 420-nm species, i.e. decrease of the 337-nm species and increase of the 420-nm species. From the pH dependence of the equilibrium between these two species, pKa of 7.9 and 7.4 was obtained for the inactive and the dithiothreitol-activated enzyme, respectively, indicating that cysteinyl residue(s) participated in lowering the pKa of the interconversion between the 337-nm species (active form) and 420-nm species (inactive form). The possible role of cysteinyl residues in the function of tryptophanase is discussed.

Catalysis↗
PubMed1983

Ligand exchange reactions of diol dehydrase-bound cobalamins and the effect of the nucleoside binding.

The inactive complex of diol dehydrase with hydroxocobalamin was resolved by treatment with SO2-3, followed by dialysis to remove SO2-3, giving the apoenzyme which was reconstitutable into catalytically active holoenzyme upon addition of adenosylcobalamin ("re-activation"). Spectral evidence showed that the enzyme-bound hydroxocobalamin undergoes a Co beta-ligand exchange reaction forming sulfitocobalamin. Sulfitocobalamin was bound to diol dehydrase only loosely, and therefore dissociated from the enzyme. In contrast, neither the enzyme-hydroxocobalamin-5'-deoxyadenosine nor the enzyme-hydroxocobalamin-adenosine complex was resolved and thus re-activated by this procedure. It was shown spectroscopically that the hydroxocobalamin in these complexes does not react with SO2-3, or even with CN-, indicating that the OH group in the Co beta-position was blocked spatially by these enzyme-bound nucleosides. Neither O2-inactivated holoenzyme nor the holoenzyme inactivated suicidally by glycerol or 1,2-ethanediol during dehydration reaction was also re-activated by the same procedure. The complex of the enzyme with cyanocobalamin or methylcobalamin was not resolvable by the SO2-3 treatment. This was because these cobalamins bound to the enzyme were not subject to a ligand exchange reaction with SO2-3.

Cobamides↗
PubMed1983

Formation of thieno[3,2-g]pterines from the molybdenum cofactor.

A fluorescent oxidation product of the molybdenum cofactor was isolated from Escherichia coli nitrate reductase (EC 1.9.6.1) and bovine milk xanthine oxidase (EC 1.2.3.2), which showed a visible absorption band at 395 nm and was dephosphorylated by alkaline phosphatase but not by phosphodiesterase I. The dephosphorylated species was oxidized by periodate to thieno[3,2-g]pterin-2-carbaldehyde which was quantitatively converted to thieno[3,2-g]pterin-2-carboxylic acid by subsequent treatment with Ag2O in 2 N NaOH. These results indicate that the oxidation product of the molybdenum cofactor is a thieno[3,2-g]pterin derivative with an unidentified side chain in the 2 position.

Animals↗
PubMed1982

The mechanism of in sutu reactivation of glycerol-inactivated coenzyme B12-dependent enzymes, glycerol dehydratase and diol dehydratase.

In the previous paper (S. Honda, T. Toraya, and S. Fukui, J. Bacteriol., 143, 1458-1465 (1980)), we reported that the glycerol-inactivated holoenzymes of adenosylcobalamin-dependent glycerol dehydratase and diol dehydratase are rapidly and continually reactivated in toluene-treated cells (in situ) by adenosine 5'-triphosphate (ATP) and divalent metal ions in the presence of free adenosylcobalamin. To elucidate the mechanism of this in situ reactivation, the nature of the binding of various irreversible cobalamin inhibitors to the dehydratases in situ was investigated. In the presence of ATP and Mn2+, enzyme-bound hydroxocobalamin, cyanocobalamin and methylcobalamin were rapidly displaced by added adenosylcobalamin. Without ATP and Mn2+, such displacement did not take place. In contrast, enzyme-bound adeninylbutylcobalamin and adenosylethylcobalamin were essentially not displaceable by the free coenzyme even in the presence of ATP and Mn2+. Inosylcobalamin was a very weak inhibitor irrespective of the presence of ATP and Mn2+. These results indicate that the relative affinity of the enzymes in situ for the cobalamins with simple Co beta ligands was markedly lowered in the presence of ATP and Mn2+, whereas that for the cobalamins with adenine-containing ligands was not. When the glycerol-inactivated holoenzymes in situ were dialyzed against a buffer containing ATP and Mg2+, the inactivated coenzyme moiety dissociated from the enzymes leaving apoproteins. Kinetic evidence was also obtained with the dehydratases in situ that continual displacement of the inactivated coenzyme moiety by adenosylcobalamin takes place during the glycerol dehydration reaction in the presence of ATP and Mn2+. Since the adenosyl group of the bound coenzyme is irreversibly removed from the cobalamin moiety during inactivation by glycerol, all of these data constitute clear evidence that the inactivated holo-dehydratases are reactivated in situ in the presence of ATP and Mn2+ by displacement of the modified coenzyme moiety by free intact adenosylcobalamin (i.e. selective B12-exchange mechanism).

Adenosine Triphosphate↗
PubMed1981

Modification of tryptophanase with tetranitromethane.

Modification of apotryptophanase with tetranitromethane [C(NO2)4] resulted in a loss of enzymatic activity, whereas holotryptophanase was highly resistant against C(NO2)4-inactivation. The essential importance of the active-site-bound pyridoxal 5'-phosphate (pyridoxal-P) for the protection was confirmed by the agreement of K 1/2 (protection) (1.2 microM) for pyridoxal-P with Km (1.5 microM) in enzyme catalysis. Amino acid analyses and inactivation stoichiometry showed that modification of 1--2 tyrosyl residues per monomer caused complete inactivation. The appearance of 430-nm species upon incubation of C(NO2)4-inactivated apoenzyme with pyridoxal-P indicated that the C(NO2)4-inactivated apoenzyme could still bind the coenzyme, although an affinity of the enzyme for pyridoxal-P (Kd = 51 microM) was much lower than that of the native enzyme (Kd = 0.7 microM). A close relationship was observed between the cofactor activity of monovalent cations and their effectiveness in the protection by pyridoxal-P: in the presence of active monovalent cations (K+, NH+4 and Rb+) pyridoxal-P could provide the protection but not in the presence of inactive cations (Li+, Na+ and Cs+) as well as in the absence of inorganic monovalent cations. From the experimental results obtained it was suggested strongly that tryptophanase has essential tyrosyl residues near the active site. The tyrosyl residues were prevented from the attack of C(NO2)4 by the active-site-bound pyridoxal-P only in the catalytically active holoenzyme.

Amino Acids↗