Enzyme Catalyzed Degradation and Formation of Peroxycarboxylic Acids

The ability of hydrolases to catalyze perhydrolysis, i.e. lysis of acyl substrates with hydrogen peroxide to form peroxycarboxylic acids, has been investigated. Lipases, esterases and cholinesterases were found to catalyze perhydrolysis but the preference of the enzymes for hydrogen peroxide relative to water as nucleophile was only 10-100 fold, even in the best cases. Hence, perhydrolysis proceeds with a very low efficiency in aqueous systems. Furthermore, all lipases, esterases and cholinesterases tested degrade peroxycarboxylic acids to the corresponding carboxylic acid and hydrogen peroxide. This reaction is most pronounced in the case of lipases while less so for cholinesterases. Consequently, cholinesterases are superior to the other hydrolases studied in catalyzing net formation of peracids in aqueous systems. In organic solvents, immobilized lipases efficiently catalyze formation of peracids from either triglycerides or the parent carboxylic acid. Proteases and phospholipase A-2 were found to neither degrade peracids nor catalyze perhydrolysis of carboxylic esters or phospholipids, respectively.     

Kinetic characterization of carboxypeptidase-Y-catalyzed peptide semisynthesis Prediction of yields

Summary Carboxypeptidase-Y-catalyzed peptide semisynthesis has been characterized at pH 7.5, 25°C from initial rate steady state kinetic and progress reaction studies of hydrolysis and aminolysis of-N-benzoyl-L-tyrosine 4-nitro-anilide using the natural L-amino acids and their amides as nucleophiles. The reaction mechanism previously shown to account for carboxypeptidase-Y-catalyzed aminolysis reactions (Christensen et al., 1992) was found also to account for all of the reactions studied here. It involves in addition to the classical serine proteinase mechanism: i) complex formation between the free enzyme and the nucleophile, an interaction characterized by the competitive inhibition constant,K _i, and ii) reaction of the nucleophile with the acylated enzyme forming a complex of enzyme and aminolysis product, characterized by the aminolysis kinetic parameter,K _N.A competitive inhibitory effect showing binding to the free enzyme is seen mainly with large hydrophobic amino acids and their amides i.e. the same residues as those preferred on either side of the scissile bond in carboxypeptidase-Y substrates. The stoichiometry of the inhibition is 1 : 1 and the actual binding position most likely is that of the leaving group of substrates,S ₁.Aminolysis effects are obtained with a wide range of amino acids and amino acid amides, exceptions are Pro and, probably due to their low solubility, Tyr, Trp, Asp and Glu. TheK _N-values show relatively little dependence on the chemical nature of the side groups, but a marked difference between the amino acid and its amide. The amides interact more strongly. The kinetic parameter,k _c/K_m, of the hydrolysis of the aminolysis products is another important factor in peptide semisynthesis. Thek _c/K_m-values obtained of the amidated aminolysis products are much less than those of the products formed with free amino acids. All in all this leads to rather efficient aminolysis with the L-amino acid amides and poor aminolysis with the L-amino acids.Abbreviations BzTyrNHPhNO₂ -N-benzoyl-L-tyrosinyl 4-nitro-aniline - Xaa L-amino acids - Xaaa L-amino acid amides - Z-Phe Carbobenzoxy-L-phenylalanine - Z-Met Carbobenzoxy-L-methionine - BzTyr -N-benzoyl-L-tyrosine - AlaVal L-alanyl-L-valine - ValAla L-valyl-L-alanine     

Experimental Infection of Danish Landrace/Yorkshire Crossbred Pigs with Schistosoma japonicum from the People’s Republic of China

This study was undertaken to assess the suitability of Danish Landrace/Yorkshire (L/Y) crossbred pigs as experimental hosts of a Chinese mainland strain of Schistosoma japonicum. Pigs were exposed to 200, 500 or 1000 cercariae and parasite burdens were determined by perfusion after either 8 or 11 weeks. All pigs became infected with onset of faecal egg excretion 6 to 7 weeks following exposure to cercariae. The pattern of faecal egg excretion differed markedly among the individual animals. Gross hepatic pathological lesions of varying degrees were noted in all of the pigs. Schistosome worm recoveries ranged from 1.5–23.4% of the cercarial exposure dose. Most schistosome eggs recovered from the tissues, expressed as eggs/g tissue, were found in the rectum (91%), caecum (3.1%) and liver (5.1%). The results show that Danish L/Y pigs may serve as appropriate experimental final hosts of the Chinese mainland strain of S. japonicum.     

Metabolic suppressors of trimethoprim and ultraviolet light sensitivities of Saccharomyces cerevisiae rad6 mutants.

Dominant mutations at two newly identified loci, designated SRS1 and SRS2, that metabolically suppress the trimethoprim sensitivity of rad6 and rad18 strains, have been isolated from trimethoprim-resistant mutants arising spontaneously in rad6-1 rad18-2 strains of the yeast Saccharomyces cerevisiae. The SRS2 mutations also efficiently suppress the ultraviolet light sensitivity of the parent strains. They do not, however, suppress their sensitivity to ionizing radiation or their deficiency with respect to induced mutagenesis and sporulation. Such observations support the hypothesis that RAD6-dependent activities can be separated into two functionally distinct groups: a group of error-free repair activities that are responsible for a large amount of the radiation resistance of wild-type strains and also for their resistance to trimethoprim, and a group of error-prone activities that are responsible for induced mutagenesis and are also important in sporulation, but which account at best for only a very small amount of wild-type recovery.     

Theophylline, otentiation of testosterone propionate or estradiol bensoate in inducing male but not female sexual behavior in the female rat.

Two experiments were carried out to assess the possible involvement of 3′:5′cyclic adenosine monophosphate (cAMP) in the hormonally mediated activation of masculine and feminine sexual behavior in female rats. In Experiment I, theophylline, a compound shown to be effective in inhibiting the degradation of cAMP, was combined with estradiol benzoate (EB) in an attempt to potentiate the action of estradiol for inducing feminine or masculine sexual behavior. Theophylline, when administered in combination with EB to ovariectomized females, resulted in an increase in masculine sexual behavior but no potentiating action on female receptivity. In Experiment II, theophylline, when given to female rats, potentiated the action of testosterone propionate in stimulating male but not female sexual behavior. These data suggest that estradiol and testosterone may be activating masculine sexual behavior through similar biochemical mechanisms. Likewise, cAMP may be involved in the activation of masculine but not feminine sexual behavior by gonadal steroids.     

Incidence of zearalenol (Fusarium mycotoxin) in animal feed.

Zearalenol, the reduction product of zearalenone produced by Fusarium roseum growing in cereals, was found for the first time naturally occurring in oats and corn. This metabolite is three to four times more active estrogenically than zearalenone.     

The influence of small atmospheric ions on human well-being and mental performance

Two experimental series were carried out to investigate a possible influence of small atmospheric ions on human beings under well-controlled conditions. In Experiment I, six female subjects were individually exposed in a climatic chamber to high concentrations of positive atmospheric ions, negative atmospheric ions and no ions. Physiological measurements were made, mental performances were tested and subjective votings were recorded. No significant effects of positive or negative atmospheric ions were found. — in Experiment II, 12 male and female subjects were selected out of 125 persons, all tested individually for feeling of discomfort when exposed to positive air ions in short selection experiments. These subjects were exposed twice to the same three ion conditions as in Experiment I. For the selected subjects no significant influence of the ions was found.Presented at the Second Colloquim Bioklimatische Wirkungen luftelektrischer und elektromagnetischer Faktoren, Technische Universität, Munich 16–18 September 1976.     

Perturbed angular correlation gamma ray (PAC) spectroscopy of 111Cd carboxypeptidase A alpha.

The active center of Cd(II) carboxypeptidase A has been examined by means of perturbed angular correlation of gamma rays as a function of pH. This method simultaneously detects changes in coordination geometry, in the charge of groups within 5 Å of the metal nucleus and delineates multiple states of the active center. Carboxypeptidase A crystals exhibit one predominant state while several are present in solution. Interpretation of the experimental data in terms of Angular Overlap Theory suggests the species characteristic of the crystals has a distorted tetrahedral coordination geometry and is in equilibrium with a pentacoordinated species in solution.