ABSTRACT
Aspergillus flavus and Aspergillus parasiticus produced ethylene during early growth. However, the onset of toxin biosynthesis was marked by the absence of ethylene evolution. 2-Chloroethyl phosphonic acid, an ethylene-generating compound, inhibited aflatoxin biosynthesis in vivo. The reciprocal relationship between the production of aflatoxin and ethylene by the organism may indicate the involvement of the latter in the regulation of aflatoxin biogenesis.
Subject(s)
Aflatoxins/biosynthesis , Aspergillus flavus/metabolism , Aspergillus/metabolism , Ethylenes/biosynthesis , Aspergillus/drug effects , Aspergillus/growth & development , Aspergillus flavus/growth & development , Culture Media , Organophosphorus Compounds/pharmacology , Species Specificity , Time FactorsABSTRACT
Immobilized beta-galactosidase was obtained by crosslinking the enzyme with hen egg white using 2% glutaraldehyde. The gel obtained could be lyophilized to give a dry enzyme powder. The pH optimum of both the soluble and immobilized enzyme was found to be 6.8. The immobilized enzyme showed a higher K(m) for the substrates. The extent of enzyme inhibition by galactose was reduced upon immobilization. The stability towards inactivation by heat, urea, gamma irradiation, and protease treatment were enhanced. The bound enzyme as tested in a batch reactor could be used repeatedly for the hydrolysis of milk lactose. The possible application of this system for small-scale domestic use has been suggested.
Subject(s)
Blood Coagulation , Blood Proteins/metabolism , Fibrinolysis , Animals , Blood Proteins/physiology , Male , Methylation , Rats , Rats, Inbred StrainsSubject(s)
Prothrombin/metabolism , Thrombin/metabolism , Enzyme Activation , Humans , Kinetics , Spectrophotometry, UltravioletABSTRACT
A stable immobilized preparation of fumarase (EC 4.2.1.2) was obtained by entrapment of rat liver mitochondria in acrylamide polymerized by using gamma irradiation (100 kR). The enhanced stability and the efficiency of the entrapped enzyme have shown potential for repeated use for the production of L-malic acid from fumaric acid. The possible formation of succinic acid in the system could be controlled by incorporating malonate along with detergents such as sodium deoxycholate or sodium dodecylsulfate in the reactor system.
ABSTRACT
The effect of gamma-irradiation on purified prothrombin and thrombin in aqueous solution has been assessed with reference to bifunctional activities, e.g., clotting and esterase functions, physico-chemical changes in structure, and kinetics. The inactivation curves indicated that the clotting activity was more susceptible to gamma-radiation than the esterolytic function in both the proteins. Prothrombin was comparatively more sensitive to radiation than thrombin. The irradiation of prothrombin (100 kR) caused modifications in the protein resulting in reduced formation of thrombin after activation by Factor Xa. The modifications caused by irradiation were assessed in these proteins by changes in spectral characteristics, levels of tryptophan and disulphides, electrophoretic mobility and amino acid composition. Radiation-induced changes in thrombin were reflected in its kinetic behaviour. The clotting activity of thrombin was almost completely lost at 100 kR, while esterolysis was relatively less affected. The modification of tyrosine and tryptophan residues in thrombin influenced the clotting activity, while these were not involved for esterolysis. Histidine had involvement in both these activities.
Subject(s)
Prothrombin/radiation effects , Thrombin/radiation effects , Amino Acids/analysis , Animals , Blood Coagulation/drug effects , Cattle , Dose-Response Relationship, Radiation , Fibrinogen/metabolism , Hydrolysis , Kinetics , Spectrometry, Fluorescence , Tosylarginine Methyl Ester/metabolismABSTRACT
The influence of the inoculum size on growth and aflatoxin production was examined in Aspergillus parasiticus (NRRL 3145) by using a synthetic medium. The reduction in the number of spores by 4 to 5 log cycles either by serial dilution or by gamma irradiation caused a two fold increase in the toxin production. The decrease in the inoculum size induced a lag in growth of the culture, though the final yield of the mycelium over the 28-day experimental period was the same. The maximal accumulation of aflatoxin was observed on day 14 of incubation. A transition from the biphasic to monophasic pattern in aflatoxin production could be correlated with the size of the inoculum. The enhanced toxin production from dilute inocula was similar to that obtained with the surviving fraction of the spores after gamma irradiation (0 to 150 krads).
Subject(s)
Aflatoxins/biosynthesis , Aspergillus/metabolism , Aspergillus/growth & development , Aspergillus/radiation effects , Gamma Rays , Spores, Fungal/physiologyABSTRACT
Phosphoglucose isomerase (D-glucose-6-phosphate ketolisomerase, EC 5.3.1.9) purified to homogeneity from Lactobacillus casei was used for studies on 2H2O effects. This preparation showed distinct differences in functional properties in H2O and 2H2O, respectively. Erythrose-4-phosphate which exerted sigmoidal inhibition in H2O, acted as a competitive inhibitor in 2H2O. The enzyme also showed reduced rate of fructose 6-phosphate formation in 2H2O. The enzyme was found to be dimeric in water and monomeric in 2H2O. The loss of regulatory properties of the enzyme has been correlated with disaggregation of the protein in heavy water, similar to that caused by sodium dodecyl sulphate treatment.
Subject(s)
Deuterium/pharmacology , Glucose-6-Phosphate Isomerase/metabolism , Lacticaseibacillus casei/enzymology , Glucose-6-Phosphate Isomerase/antagonists & inhibitors , Macromolecular Substances , Molecular Weight , Sugar Phosphates/pharmacology , UltracentrifugationABSTRACT
Phosphoglucose isomerase (D-glucose-6-phosphate ketolisomerase, EC 5.3.1.9), purified from Lactobacillus casei, showed multiplicity with respect to electrophoretic mobility, molecular weight, kinetic properties and responses to erythrose 4-phosphate. Among the three forms isolated, one having a dimeric conformation, was specific for glucose 6-phosphate. Erythrose 4-phosphate inhibited this preparation in a sigmoid fashion, while this compound activated the enzyme for isomerization of ribose 5-phosphate. In tetrameric conformation of the similar subunits, the enzyme was more specific for ribose 5-phosphate and the inhibition exerted by erythrose 4-phosphate was hyperbolic. The possible implications of these observations have been discussed.
Subject(s)
Glucose-6-Phosphate Isomerase/isolation & purification , Lacticaseibacillus casei/enzymology , Chromatography, Gel , Chromatography, Ion Exchange , Electrophoresis, Polyacrylamide Gel , Glucose-6-Phosphatase/metabolism , Glucose-6-Phosphate Isomerase/antagonists & inhibitors , Hydrogen-Ion Concentration , Kinetics , Macromolecular Substances , Molecular Weight , Ribosemonophosphates/metabolism , Sugar Phosphates/pharmacologyABSTRACT
A multienzyme complex consisting of invertase, glucose oxidase, and catalase was reconstituted by binding glucose oxidase using concanavalin A (Con A) to the cell wall of Sacchararomyces cerevisiae, previously induced for maximal activities of invertase and catalase. The cell flocculate obtained was stabilized by entrapment in polyacrylamide using γ irradiation at 100 kR. This complex showed a shortening of the lag period and enhancement in gluconic acid production as compared to a similar mixture of soluble enzymes. The efficacy of the multienzyme complex has been compared with that of mixed multienzyme system composed of individually immobilized enzymes. The immobilized multienzyme complex in a continuous-flow stirred-tank reactor system could be operated for continuous conversion of sucrose to fructose and gluconic acid. The reactor system did not show any loss in efficiency in a continuous operation over 20 days.
