Showing papers in "Bioorganic Chemistry in 1975"

TL;DR: In this article, the aglycone chirality of naringin has been studied as a function of grapefruit maturity and it is concluded that the (2 S ) isomerization in ripening grapefruit is not responsible for debittering.

TL;DR: In this paper, cyclohexaamylose-N-(N,N′ -dimethylaminoethyl)acetohydroxamic acid and cyclohexamyloses-N -(4-imidazolemethyl)acethesynylacethodosamic acid were synthesized.

TL;DR: In this paper, three thermal peptide fractions of the diffusible fraction were isolated using trifluoracetic acid (TFA) hydrolysis to open the blocked N-terminal group before performing the dansylation reaction.

TL;DR: Evidence is presented suggesting that hepatic isomerase-catalyzed rearrangements of hydroxylamines proceed via pathways analogous to those described for chemical model systems, and appears to be intermolecular involving the generation of a resonance-stabilized nitrenium ion capable of binding to amino acids and nucleotide bases.

TL;DR: In this paper, a mechanism involving electrostatically induced torsional activation of the scissile peptide bond, Lewis acid coordination of zinc to amide carbonyl, proton donation from Glu 270 to the amide nitrogen, with concerted attack by solvent water was considered.

TL;DR: In this article, the structure of malformin A 1, a metabolic product of Aspergillus niger, was reexamined and the sequence of its amino acid constituents established as The cyclopentapeptide-disulfide corresponding to this structure was prepared through stepwise synthesis of the protected pentapeptides derivative, benzyloxy-carbonyl- l -isoleucyl-S -benzyl- d -cysteinyl- S -benzinyl-d -cysteyl-

TL;DR: In this article, experiments with biomimetic synthesis of alkaloids by intramolecular oxidative phenol and nonphenol coupling reactions are described, and a new synthesis of the alkaloid colchicine is presented.

TL;DR: In this article, a new reagent system for selective brominative cyclization of polyenes is presented. But the mechanism of Br + -formation in nature is discussed on the basis of the new re-agent system.

TL;DR: The results indicate that the enzyme involved exhibits a marked specificity for ergosta-5,7,22,24(28)-tetraen-3β-ol and support the concept of a major terminal step in ergosterol biosynthesis.

TL;DR: In this paper, a water-soluble polymer catalyst was prepared by radical polymerization of protected hydroxamate monomer, 1-methyl-2-vinylimidazole and acrylamide, and by the subsequent NH 2 NH 2 treatment of the polymer.

TL;DR: In this article, the rate constants for isomerization of the E1H isomer (pKa 8 in H2O) of ribonuclease-A to the E2H iso-isomer (PKa = 6.1 in H 2O), determined from proton-uptake measurements by the temperature-jump technique, in mixtures of protium and deuterium oxides, were described by the equation k12n = (733 ± 16)(1 − n + [0.46 ± 0.04]n)2sec−

TL;DR: In this paper, a 2-dimethylaminoethylacetohydroxamic acid was synthesized, and the deuterium oxide solvent isotope effect on the azide ion reaction of the intermediate was investigated.

TL;DR: Desthiomalformin, cyclo-d -alanyl-d-alanyl, d - alanyl- d -al-anyl- l -valyl- d-leucyl-l -isoleucyl, was synthesized by conventional methods as mentioned in this paper.

TL;DR: The synthesis of several specifically substituted pyridoxine derivatives 5, 6, 7, 8, 9, 10, 11, and 12 is described, and the mechanism is discussed as a model for a new type of pyrIDoxine transformation, either in known vitamin-B 6 -dependent enzymatic reactions or in toxicological reactions induced by pyridine.

TL;DR: Fluorescent 1, N 6 -ethenoadenosine derivatives of adenosine triphosphate, adenoine diphosphate and nicotinamide adenine dinucleotide have been prepared and nuclear magnetic resonance and mass spectrum data indicate that only the purine ring has been modified.

TL;DR: The results of the alkylation study indicate that the nucleophilic, active histidine molecule is coordinated to the copper(II) ion through the amino nitrogen and a carboxylate oxygen with the imidazole group turned away from the copper.

TL;DR: The predominant reaction of lysozyme with 2-hydroxy-5-nitrobenzyl bromide leads to the formation of an enzymatically inactive, labile product substituted at tryptophan 62, and a tentative mechanism for the hydrolysis reaction is presented.

TL;DR: It is concluded that the histidine residues of the proteins examined have reacted with formaldehyde to form N-hydroxymethyl derivatives and is in agreement with a previous report from the authors' laboratories suggesting that His-57 is not the only site of reaction of TPCK with chymotrypsin.

TL;DR: In this article, it was shown that presqualene pyrophosphate is not an artifact, but a true intermediate in the biosynthesis of squalene, and that the precursors of precursory molecules are not artifacts.

TL;DR: Based on spectral similarities to appropriate model compounds and structural analysis of the intermediate after its reduction by sodium borohydride, the intermediate has been tentatively identified as the Δ 4 -3-imine.

TL;DR: In this article, the second-order reaction of p-nitrophenyl acetate with lysine and its derivatives has been investigated in water-dioxane solutions over the pH range 8.1-10.1.

TL;DR: In this paper, it was shown that 3 RS -[5-D 1 ]-lactones were diastereoisomers, both having the 5 R absolute configuration, and this conclusion was confirmed by the finding that speciments of 3-methyl[5]-pent-2-eno-5lactone made by the dehydration of 3 S −[5−D 1]-mevalonolactone and of 3 RS −[ 5−D1]-mevaldate had identical optical activities and of the same sign.

TL;DR: In this paper, various structural features of polyamines which are responsible for the acceleration of the hydrolysis of ATP to ADP and P i at pH 3-4 were surveyed by means of kinetic studies.

TL;DR: The observed rate constants for 5-bromocytosine dehalogenation increase, reach a maximum at about 4.5, and then decrease as a function of pH, which is analogous to the bisulfite-catalyzed dehalagenation of the 5-halouracils.

TL;DR: In this article, the structural requirements for substrate activity in the oxidative demethylation at C4 of steroids by rat liver enzymes were investigated and several steroids have been synthesized, labeled with tritium, and incubated with rat liver enzyme preparations.

TL;DR: The absorbance and difference absorbance spectra of pyridine-hemochromogen at different concentrations showed the presence of two different types of hemochromogens, one unstable form (compound III) at low concentration and a more stable form(compound II) at higher concentration as mentioned in this paper.

TL;DR: In this article, the reactions of pyridoxal phosphate with α-amino-α-methyldiethylmalonate have been investigated at pH 6.25 (30°C, N 2 atmosphere).

TL;DR: In this paper, an intramolecular 2-hydroxymethyl-4-nitrophenyl trimethylacetate is converted to its benzyl ester counterpart in aqueous solutions of dilute buffers.

TL;DR: The title compound, [1-β-mercaptopropionic acid, 2-(3,5-dibromo- l -tyrosine)]-8-lysine-vasopressin (X), was synthesized by condensation of Pro-Lys(Boc)-Gly-NH 2 with the cyclic peptide, which is qualitatively identical to the corresponding analog of oxytocin, although it is a less potent antagonist than the latter compound.

TL;DR: The results suggest either that an epimerizing enzyme is present in the soluble fraction or that two enzymes, each specifically forming one of the two enantiomers, are present.