Inactivation of dioldehydrase in the presence of a coenzyme-B12 analog

We have previously shown that a coenzyme-B₁₂ analog, adenosylcobalamin (AdoCbl)-(e-OH), with the e-propionamide group converted to a carboxylic acid, serves as a poor coenzyme for dioldehydrase. During the course of the catalytic process, the enzyme AdoCbl-(e-OH) complex becomes catalytically inactive (T. Toraya, E. Krodel, A. S. Mildvan, and R. H. Abeles, 1979, Biochemistry18, 417–426). We have now examined the mechanism of this inactivation further. Inactivation only occurs in the presence of substrate. The dioldehydrase coenzyme analog complex is stable in the absence of substrate. In the inactivated complex, the coenzyme analog was stoichiometrically converted to a cob(II)alamin species. The cob-(II)alamin formed remained irreversibly bound at the active site of the enzyme and resisted oxidation by O₂ even in the presence of CN^?. Stoichiometric formation of 5′-deoxyadenosine from the 5′-deoxy-5′-adenosyl moiety of the coenzyme analog was demonstrated with [8-¹⁴C]-AdoCbl(e-OH). This nucleoside also remained tightly bound to the enzyme and was not exchangeable with free 5′-deoxyadenosine nor was it removed by Sephadex chromatography. The rate of inactivation showed no deuterium isotope effect when the inactivation occurred in the presence of l,2-propanediol-l-d₂. The inactivated complex was resolved by acid ammonium sulfate treatment into the intact apoenzyme and the hydroxocobalamin derivative. This indicates that the apoenzyme itself is not modified in the inactivation process. These results suggest that the inactivation reaction occurs from one of the intermediates in the normal catalysis. We propose that the inactivation is due to incorrect binding of the modified coenzyme in an intermediate of the catalytic process. This incorrect binding leads to the loss of the substrate radical, and consequently, to loss of catalytic activity.     

Coenzyme B12-dependent diol dehydrase: Chemical modification with 2,3-butanedione and phenylglyoxal

The apoenzyme of diol dehydrase was inactivated by two arginine-specific reagents, 2,3-butanedione and phenylglyoxal, in borate buffer. In both cases, the inactivation followed pseudo-first-order kinetics. Kinetic data show that the incorporation of a single reagent molecule per active site of the enzyme is necessary for the complete inactivation. The modification with 2,3-butanedione was reversed by dilution of the reagent and borate concentrations (65% activity recovered). 1,2-Propanediol (substrate) partially protected the enzyme against inactivation. The holoenzyme was almost insensitive to 2,3-butanedione and phenylglyoxal, indicating that the essential arginine residue is prevented from the attack of these reagents either by direct blockage with the bound coenzyme or by an indirect conformational change caused by coenzyme binding. The inactivation of diol dehydrase by 2,3-butanedione did not result in dissociation of the enzyme into subunits. From these results, we concluded that the essential arginine residue is located at or in close proximity to the active site of diol dehydrase.     

Stereoselective hydrolysis of dl-menthyl succinate by gel-entrapped Rhodotorula minuta var. texensis cells in organic solvent

Summary dl-Menthyl succinate was successfully hydrolyzed stereoselectively by Rhodotorula minuta var. texensis cells entrapped within photo-crosslinked or polyurethane resin gels in water-saturated n-heptane. The hydrolyzed product was found to be pure l-menthol. The catalytic activity of the immobilized cells, especially those entrapped in urethane polymers, was far more stable than that of the free cells. The half-life of the polyurethaneentrapped cells was estimated to be 55–63 days in the organic solvent.Dedicated to the 65th birthday od Professor Dr. G. Manecke     

Relationship between phosphate content and immunochemical properties of subfractions of bakers'' yeast mannan.

The mannan of bakers' yeast (Saccharomyces cerevisiae) was fractionated on a column of diethylaminoethyl-Sephadex into five subfractions. Phosphate content of these mannan subfractions was proportional to the concentration of NaCl solutions used in the chromatographic separation. Quantitative precipitin reactions showed that the serological reactivities of the subfractions were proportional to the content of phosphate. The result of acetolysis study showed that the amounts of mannotetraose and phosphate-containing oligosaccharide fractions increased proportionally to the acidity, whereas the amount of mannose decreased inversely. The results from quantitative precipitin reaction tests and acetolysis study demonstrated that both phosphate contents and multiplicity of branching moieties of mannan subfractions increased proportionally, i.e., micro-heterogeneity concerning the acidity comprised in the parent bulk mannan is not attributable merely to the coexistence of molecular species containing different amounts of phosphate but also to the presence of more of the branching moieties.     

Effect of furosemide on urinary excretion of prostaglandin E in normal volunteers and pateints with essential hypertension

Urinary excretion of prostaglandin E was measured radioimmunologically in 19 healthy persons ( 15 men and 4 women ) and in 16 patients ( 10 men and 6 women ) with essential hypertension before and after the administration of furosemide. The excretion rates were increased from 26.3±3.0 to 64.5±11.3 ng/hr in the former and from 11.9±2.7 to 26.9±85 ng/hr in the latter. There was a significant difference between them, healthy subjects showing a greater increase than patients with essential hypertension.There was an obvious sexual difference in urinary excretion of prostaglandin. In men, greater increase in the excretion rates was found than in the women. Greater increases were also obtained in healthy men than in hypertensive men and in healthy women than in hypertensive women. The present results suggest that furosemide enhances urinary excretion of prostaglandin E by mechanisms which entails either an increase in prostaglandin synthesis or a decrease in renal metabolism.     

Antibacterial and bactericidal activities of tea extracts and catechins against methicillin resistant Staphylococcus aureus]

We examined tea extract, (-) epigallocatechin gallate (EGCg) and theaflavin digallate (TF3) for their antibacterial and bactericidal activities against methicillin resistant Staphylococcus aureus (MRSA) and food poisoning strains of S. aureus. Twenty percent tea extract (50 microliters), EGCg (63 micrograms) and TF3 (125 micrograms) added to one ml of culture medium each inhibited the growth of all strains of MRSA and food poisoning S. aureus tested. Tea extract showed also a bactericidal activity against MRSA even at the same concentration of as in ordinarily brewed tea. EGCg at a concentration of 250 micrograms/ml showed a bactericidal activity against MRSA but not against food poisoning S. aureus, but at 500 micrograms/ml reduced markedly the viable number within 48h. These results suggest that tea and catechin can be used as prophylactic agents against MRSA infection.     

Characterization of proteins released from legume seeds in hot water.

When immersed in water at 50-60 degrees, mature soybean seeds release a large amount of protein. The major protein released was basic 7S globulin (Bg), which is present in the cotyledons of soybean seeds. The released Bg consisted of the 27,000 and 16,000 subunits which were linked by disulphide bonding and glycosylated. The released Bg exhibited an identical structure with the mature Bg which was synthesized in the normal developing seeds. Proteins like Bg were also found to be released into hot water from the seeds of legume species such as azuki-bean, cowpea, mung-bean and winged-bean. Besides Bg and Bg-like proteins, a few proteins including the 9,000 hydrophobic protein in soybean, ubiquitin in cowpea and mung-bean, and Kunitz trypsin inhibitor in winged-bean, were released from the seeds in hot water.     

Double-Blind Study of the Chronopharmacotherapy of Depression

To investigate the possibility of chronotherapy with antidepressants for patients with depression, we gave single daily doses of clomipramine 150 mg/day to 30 patients with depression at three different times of day, i.e., morning, noon, or before bedtime, using a double-blind method over a 4-week period. Beneficial effects differed according to the administration time of day, with the most effective result being found for the administration at noon. Time-dependent differences in side effects were observed in tremors and dryness of mouth. An additional 10 patients were administered their medications three times a day by traditional, equally divided doses, and the efficacy was inferior than daily single doses at noon. The study results showed the significance of the administration time of day for the benefits and side effects of antidepressant therapy for depression.