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PubMed1976

Nucleophilic addition reactions of free and enzyme-bound deazaflavin.

DeazaFMN-containing glycolate oxidase has been prepared and shown to catalyze the stereospecific transfer of the alpha-hydrogen from substrate to enzyme-bound deazaFMN. The reaction of sulfite, cyanide, and hydroxylamine with several deazaflavin-containing enzymes (glycolate oxidase, D-amino acid oxidase, glucose oxidase, N-methylglutamate synthetase) and free deazaFMN has been examined. All the deazaflavin systems tested form reversible 1:1 complexes with sulfite and cyanide. The pH dependence of the reaction of free deazaFMN with cyanide indicates that cyanide anion is the reacting nucleophile. Hydroxylamine complexes are formed with deazaFMN glycolate oxidase and deazaFAD glucose oxidase. The effectiveness of the various nucleophilic reagents in complex formation decreases in the following order: sulfite greater than cyanide greater than hydroxylamine. The relative stability observed for the sulfite and cyanide complexes formed with various deazaflavin systems (glycolate oxidase greater than D-amino acid oxidase greater than free deazaFMN) follows the same trend observed for the stability of the sulfite complexes formed with the corresponding flavin system. A correlation is also observed between the reduction potential (E'o) of the deazaflavin system (glycolate oxidase (- 170 mV) greater than D-amino acid oxidase (-240 mV) greater than free deazaFMN (-178 mV) and the stability of the deazaflavin-nucleophile complexes. The following evidence indicates that deazaflavin systems are generally more susceptible toward nucleophilic attack than corresponding flavin system: (a) with the exception of glucose oxidase, the dissociation constants for the deazaflavin-sulfite complexes are at least 1 order of magnitude less than the corresponding flavin sulfite complexes; (b) the least reactive nucleophile, hydroxylamine, does not form a complex with any of the flavin systems. In the case of cyanide, a complex is formed only with native glycolate oxidase, which is the flavin-containing system most susceptible to attack by the more reactive sulfite. Formation of the various (deaza)flavin-nucleophile complexes is characterized by a bleaching of the longer wavelength absorption band of the chromophore and increases in absorption below the isosbestic point of the reaction in the near-ultraviolet region of the spectrum. These results are consistent with the formation of covalent adducts via attack of the various nucleophiles at position 5 of (deaza)flavin. The reaction with cyanide provides the first example of a reversible addition of carbanion to enzyme-bound (deaza)flavin.

Alcohol Oxidoreductases↗
PubMed1976

Reduced nicotinamide adenine dinucleotide phosphate, a structural and conformational probe of chicken liver fatty acid synthetase.

Structural and conformational organization of chicken liver fatty acid synthetase has been probed using its fluorescent coenzyme, NADPH. Three NADPH binding sites per mole of the enzyme complex, of apparently identical dissociation constant (KD = 0.6 muM) can be titrated at temperatures above 12 degrees. These results are in disagreement with the earlier studies of Hsu and Wagner (Hsu, R. Y., and Wagner, B. J. (1970) Biochemistry, 9, 245-251) in which four such sites could be titrated. At 12 degrees, the composite sites split into two subsets: a pair of sites with a KD of 0.3 muM and a third site with a Kd of 1.1 muM. At lower temperatures (5 degrees or 2 degrees), the site with weak affinity disappears, leaving a pair of sites with a Kd of 0.5 muM. Similar observations were made when the enzyme was modified with phenylmethylsulfonyl fluoride, a specific and selective inhibitor of fatty acyl-CoA deacylase (s) of the pigeon liver enzyme complex (Kumar, S. (1975) J. Biol. Chem. 250, 5150-5158). Partial modification with phenylmethylsulfonyl fluoride elicits a NADPH binding response similar to the binding observed at 12 degrees, i.e. two sets of binding sites with nonidentical dissociation constants. Further modification corresponding to the complete loss of deacylase function results in a set of two apparently identical binding sites, and the third site is not available for titration. The modified enzyme retains the two reductase functions as measured by the model substrates, acetoacetyl-N-acetylcysteamine and crotonyl-CoA. Furthermore, the addition of acetyl- and malonyl-CoA (100 muM each) to the modified enzyme lowers the NADPH binding affinity by a factor of 3. Other observations show that the quantum yield, as measured by the ratio of fluorescence intensity of bound and free NADPH, changes with temperature and ionic strength. Lowering the temperature from 30 degrees to 2 degrees increases the enhancement ratio by 50%, whereas increase in ionic strength from 0.05 to 0.2 M potassium phosphate lowers it to 50% of the original level. Measurement of NADPH binding in the presence of NADP+, NADH, NAD+ and adenosine-2'-monophospho-5'-diphosphoribose demonstrates that NADP+ shows competitive behavior for NADPH sites (KD = 10.6 muM), whereas NADH and NAD+ show noncompetitive (KD (apparent) = nearly 600 muM) and rather complicated interactions implicating nonspecific conformational alteration of the enzyme complex. The behavior of adenosine 2'-monophospho-5'-diphosphoribose is intermediate between NADP+ and NADH. These data are discussed in terms of substrate-mediated conformational changes and the moles of each of the reductase enzymes per mole of the enzyme complex, the polarity of the NADPH binding region, and the probable structure of the nicotinamide moiety when bound to the enzyme.

Animals↗
PubMed1979

Study on dissimilatory reduction of sulphates.

A new strain of sulphate reducing bacteria was isolated from swampy forest soil. After 120 h reduction, sulphate conversion attained 100%, the molar ratio of the consumed lactate and reduced sulphate amounted to 2:1. This confirms the reduction mechanism proposed by Senez (1951).

Desulfovibrio↗
PubMed1979

[Triaminotricarboxylic amino acid oxidation productions of actinoidin and ristomycin].

Aromatic acids with three benzene nuclei bound through oxygen were obtained from actinoidin and ristomycin on their oxydation with permanganates of methylated aglycones and peptides. The structures of the methyl esters of these acids were determined by spectral methods. They are the following: methyl-3,5-bis-(4-methoxycarbonyl-phenoxy)-4-methoxybenzoate (from ristomycin) and methyl-3-(2-chlor-4-methoxycarbonyl-phenoxy)-5-(4-methoxycarbonyl-phenoxy)-4-methoxybenzoate (from actinoidin). The compounds are the aromatic parts of the molecules of the unusual triaminotricarboxylic amino acids present in the aglycones of all antibiotics of the group of polycyclic glycopeptides.

Acetylation↗
PubMed1979

The sialoglycoproteins of murine erythrocyte ghosts. A modified periodic acid-Schiff stain procedure staining nonsubstituted and O-acetylated sialyl residues on glycopeptides.

Murine erythrocyte ghosts (from DBA/2, CD-1, and B6D2 strains) contain significant amounts of O-acetylated sialyl residues, which are slowly oxidized by periodate. Sialic acids have been purified from murine erythrocyte ghosts and the existence of O-acetylated sialic acids has been confirmed: 1) by assaying with the Warren procedure before and after de-O-acetylation with 0.1 N NaOH for 45 min at 4 degrees C; 2) by thin layer chromatography on cellulose; and 3) by gas-liquid chromatography. Because these sialyl residues are unevenly distributed on the sialoglycoproteins of murine erythrocyte ghosts, the periodic acid-Schiff staining detects only one major sialoglycoprotein. A modification of the periodic acid-Schiff stain method removes these O-acetyl groups after electrophoresis and reveals two additional sialoglycoproteins which bear the majority of the O-acetylated sialyl residues. Rat erythrocyte ghosts have similar residues on one of their two sialoglycoproteins. Ghosts of human, rabbit, and guinea pig erythrocytes do not contain detectable amounts of O-acetylated sialyl residues.

Acetylation↗
PubMed1976

Oxidation of p-cresol by horseradish peroxidase compound I.

Rate constants for the reaction between horseradish peroxidase compound I and p-cresol have been determined at several values of pH between 2.98 and 10.81. These rate constants were used to construct a log (rate) versus pH profile from which it is readily seen that the most reactive form of the enzyme is its most basic form within this pH range so that base catalysis is occurring. At the maximum rate a second order rate constant of (5.1 +/- 0.3) x 10(-7) M-1 s-1 at 25 degrees is obtained. The activation energy of the reaction at the maximum rate was determined from an Arrhenius plot to be 5.0 +/- 0.5 kcal/mol. Evidence for an exception to the generally accepted enzymatic cycle of horseradish peroxidase is presented. One-half molar equivalent of p-cresol can convert compound I quantitatively to compound II at high pH, whereas usually this step requires 1 molar equivalent of reductant. The stoichiometry of this reaction is pH-dependent.

Cresols↗