Enzymatic bromination of barbituric acid and some of its derivatives

Barbituric acid, 1-methyl- and 1,3-dimethylbarbituric acid, some of its 5-phenyl derivatives, and 5-chlorobarbituric acid are presented as new substrates for the bromoperoxidase isolated from the brown alga Ascophyllum nodosum. This enzyme is able to convert these substrates into the corresponding 5-bromo or 5,5-dibromo derivatives in good yields. Kinetic measurements show that the structure of the examined substrates has little or no effect on the enzymatic rate of bromination. However, at low substrate concentration the reaction rate depends on both the concentration of the organic substrate and the concentration of hydrogen peroxide. A mechanism is proposed for the reactions of bromoperoxidase with its substrates. These reactions involve the formation of free hypobromous acid which can either brominate the organic halogen acceptor or produce singlet oxygen by a competing reaction with hydrogen peroxide.     

The chlorination of barbituric acid and some of its derivatives by chloroperoxidase

Barbituric acid and some of its derivatives are presented as new substrates for the chloroperoxidase from Caldariomyces fumago. These compounds are rapidly converted to the 5-chloro or 5,5-dichloro derivatives, in very high yield. The reaction path is discussed and the kinetics of the reactions are investigated. It is shown that neither the concentration nor the structure of the organic substrate has any influence on the rate of halogenation. The enzymatic chlorination of 1-methyl-5-phenylbarbituric acid does not proceed in a stereoselective manner. The results are compared with the present theories concerning the enzymatic reaction mechanism, and the current research on this topic is evaluated. The available data do not as yet permit a definitive choice of reaction mechanism.     

Stimulation of growth and pyruvate oxidation in Streptococcus faecalis by asparagusic acid and its derivatives

Plant growth inhibitors I, II, III, VII, VIII, which occur inasparagus, promoted growth and pyruvate oxidation in Streptococcusfaecalis 10Cl. Activities were compared with those obtainedwith -lipoic acid and several structurally related syntheticsulfur containing compounds. (Received February 21, 1973; )     

Investigation of the enzymic and electrochemical oxidation of uric acid derivatives.

The electrochemical oxidation of a number of N-methylated uric acids at the pyrolytic graphite and gold electrodes has been compared to their enzymic oxidation with type VIII peroxidase and H2O2. Spectral, electroanalytical and kinetic evidence supports the conclusion that for all compounds the electrochemical and enzymic reactions proceed by identical mechanisms.     

The enzymic oxidation of chlorogenic acid and some reactions of the quinone produced

1. Partially purified preparations of tobacco-leaf o-diphenol oxidase (o-quinol-oxygen oxidoreductase; EC 1.10.3.1) oxidize chlorogenic acid to brown products, absorbing, on average, 1.6atoms of oxygen/mol. oxidized, and evolving a little carbon dioxide. 2. The effect of benzenesulphinic acid on the oxidation suggests that the first stage is the formation of a quinone; the solution does not go brown, oxygen uptake is restricted to 1 atom/mol. oxidized, and a compound is produced whose composition corresponds to that of a sulphone of the quinone derived from chlorogenic acid. 3. Several other compounds that react with quinones affect the oxidation of chlorogenic acid. The colour of the products formed and the oxygen absorbed in their formation suggest that the quinone formed in the oxidation reacts with these compounds in the same way as do simpler quinones. 4. Some compounds that are often used to prevent the oxidation of polyphenols were tested to see if they act by inhibiting o-diphenol oxidase, by reacting with quinone intermediates, or both. 5. Ascorbate inhibits the enzyme and also reduces the quinone. 6. Potassium ethyl xanthate, diethyldithiocarbamate and cysteine inhibit the enzyme to different extents, and also react with the quinone. The nature of the reaction depends on the relative concentrations of inhibitor and chlorogenic acid. Excess of inhibitor prevents the solution from turning brown and restricts oxygen uptake to 1 atom/mol. of chlorogenic acid oxidized; smaller amounts do not prevent browning and slightly increase oxygen uptake. 7. 2-Mercaptobenzothiazole inhibits the enzyme, and also probably reacts with the quinone; inhibited enzyme is reactivated as if the inhibitor is removed as traces of quinone are produced. 8. Thioglycollate and polyvinylpyrrolidone inhibit the enzyme. Thioglycollate probably reduces the quinone to a small extent.     

Synthesis of derivatives of the RGD peptide with the residues of glutaric and adipic acids

Derivatives of the RGD peptide were prepared by the attachment of the residues of glutaric and adipinic acids to the α-amino group of L-arginine. This modification allowed condensation of these derivatives with other biomolecules or nanoparticles.