A mixed disulfide bond in bacterial glutathione transferase: functional and evolutionary implications

BACKGROUND: Glutathione S-transferases (GSTs) are a multifunctional group of enzymes, widely distributed in aerobic organisms, that have a critical role in the cellular detoxification process. Unlike their mammalian counterparts, bacterial GSTs often catalyze quite specific reactions, suggesting that their roles in bacteria might be different. The GST from Proteus mirabilis (PmGST B1-1) is known to bind certain antibiotics tightly and reduce the antimicrobial activity of beta-lactam drugs. Hence, bacterial GSTs may play a part in bacterial resistance towards antibiotics and are the subject of intense interest. RESULTS: Here we present the structure of a bacterial GST, PmGST B1-1, which has been determined from two different crystal forms. The enzyme adopts the canonical GST fold although it shares less than 20% sequence identity with GSTs from higher organisms. The most surprising aspect of the structure is the observation that the substrate, glutathione, is covalently bound to Cys 10 of the enzyme. In addition, the highly structurally conserved N-terminal domain is found to have an additional beta strand. CONCLUSIONS: The crystal structure of PmGST B1-1 has highlighted the importance of a cysteine residue in the catalytic cycle. Sequence analyses suggest that a number of other GSTs share this property, leading us to propose a new class of GSTs - the beta class. The data suggest that the in vivo role of the beta class GSTs could be as metabolic or redox enzymes rather than conjugating enzymes. Compelling evidence is presented that the theta class of GSTs evolved from an ancestral member of the thioredoxin superfamily.     

Post-thaw sperm motility, cAMP concentration and membrane lipid peroxidation after stimulation with pentoxifylline and platelet-activating factor

Earlier studies have demonstrated that pentoxifylline (PTX) and platelet-activating factor (PAF) can significantly improve the motion parameters of post-thaw human spermatozoa. This study has investigated the effects of PAF, PTX and their combination on cyclic adenosine monophosphate (cAMP) concentrations and membrane lipid peroxidation (LPO) in post-thaw human spermatozoa. Washed spermatozoa from normal volunteers (n = 10) were cryopreserved in Test-yolk buffer using a standard protocol. After 2 weeks the sperm samples were thawed, washed and incubated with either 1 microM PAF, 3 mM PTX or 0.5 microM PAF plus 1.5 mM PTX. Video sequences were recorded at 0, 30, 60, and 120 min for analysis of sperm motion parameters using the Cell Track Sperm Analysis System. Concentrations of cAMP were assessed by radioimmunoassay, and LPO levels were measured by malondialdehyde-thiobarbituric acid reactivity. Our studies indicate a time-course stimulatory effect with overall maximal stimulation observed in samples treated with the combination of PAF and PTX. The maximal stimulation of percentage motility compared to control was observed at 60 min in samples treated with PAF, PTX, or PAF plus PTX. PAF plus PTX stimulated straight-line velocity (VSL), curvilinear velocity (VCL) and lateral head displacement (ALH) after 30 min incubation. The primary effect of PAF was observed on VSL, while the main effect of PTX was on VCL. cAMP concentrations were 3-fold higher than controls in samples treated with PTX or PAF plus PTX. cAMP concentrations in PAF-treated samples did not differ significantly from controls. No significant differences were observed between any groups for LPO.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of dietary selenium on tumor induction by an oncogenic virus

Streptokinase-streptodornase (SK-SD) induced immediate and delayed skin test reactions in a high proportion of patients with disorders in which beta-streptococcal infection may be involved. The P-K test and absorption experiments with antigen or anti-IgE suggested that the immediate reaction was mediated by specific IgE antibody against SK-SD. Furthermore, the ratio of specific IgE antibody against SK-SD to total IgE was roughly calculated to be 20 percent. Finally, the RAST technique was applied to detect specific IgE antibody against SK-SD which showed high radiocounts bound to SK-SD-coupled particles in the sera of nephrotic patients who had a strong immediate reaction against SK-SD and a severe disease state.     

Initial experience of clinical pharmacology and clinical pharmacy interactions in a clinical pharmacokinetics consultation service

International statistics indicate that there is a close correlation between the consumption of saturated fats (dairy fats and meat fats) and the mortality from coronary heart disease (CHD), and this conception has been confirmed by many epidemiological studies. Such studies alone, however, cannot prove the existence of a cause-and-effect relationship between these two variables; dietary intervention trials are needed. The Finnish Mental Hospital Study was such a trial, conducted in two hospitals near Helsinki in 1959--1971. Practically total replacement of dairy fats by vegetable oils in the diets of these hospitals was followed by a substantial reduction in the mortality of men from CHD. Total mortality also appeared to be reduced. As to the causes of death other than CHD, none was significantly influenced by dietary change. This was also true for malignant neoplasms. To alleviate the burden of CHD on public health, many investigators have recommended important changes in the quantity and quality of dietary fats.