Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.1.3.9 (glucose-6-phosphatase)
 3,081 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A method is described for the incorporation of a microsomal rat liver fraction into polyacrylamide films without significant loss of its glucose-6-phosphatase activity. The enzymatic activity was completely lost when the films were prepared with ammonium persulfate as initiator of the polymerization as previously described for alkaline phosphatase, but modification of this method showed that about 90% of the glucose-6-phosphatase activity could be retained. The enzyme in the films prepared with the new method was completely inhibited by alloxan, HgCl2, and preincubation in 0.05 M acetate buffer (pH 5.0) at 37 degrees C, as determined biochemically. Similar results were obtained for the enzyme in films determined histochemically according to the lead method of Wachstein and Meisel. In this respect the behavior of the incorporated enzyme is similar to that in suspension. Films fixed with 1.5% glutaraldehyde showed rapid inactivation of glucose-6-phosphatase. There was good correlation between the biochemical and histochemical activity determined after fixation. A method to embed polyacrylamide films in Epon for electron-microscopical investigation is also described. Dimethyl sulfoxide was used as the dehydrating agent instead of ethanol/acetone.
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PMID:Cytochemical model system for microsomal rat liver glucose-6-phosphate. 18 Jan 74

Iodoacetamide, N-ethylmaleimide, p-hydroxymercuribenzoate (p-MB) and HgCl2 were tested as inhibitors of microsomal glucose-6-phosphatase. Iodoacetamide had no effect at 2 mM. N-ethylmaleimide inhibited only crude, but not purified microsomal preparations (M2) or crude microsomes exposed to deoxycholate. 14C-labelled N-ethylmaleimide was not bound by the M2 protein fraction. p-MB inhibited all types of preparations and the inhibition was not counteracted by detergent. A more detailed study was carried out with the purified M2 fraction (specific activity: 2-4 mumoles Pi/min/mg protein). Glucose-6-phosphate hydrolysis was inhibited 50% by 5 X 10(-5) M p-MB. The inhibition was completely reversible by dithiothreitol except when the enzyme was pre-incubated with p-MB in the absence of substrate. Then p-MB accelerated the temperature-dependent inactivation of glucose-6-phosphatase. Binding studies showed that around 3 mumoles 14C-p-MB were incorporated into 100 mg M2 protein regardless of the concentration of mercurial in the incubation mixture. That is, over a 25 fold range of p-MB concentration, causing up to 80% inhibition of enzyme activity, no difference was seen in the amount of labelled p-MB which was irreversibly bound to M2 protein. Kinetically p-MB behaved like a reversible inhibitor and this was confirmed by dilution experiments. Several compounds, including some amino acids, antagonized the inhibition by p-MB. The order of effectiveness was EDTA greater than barbital greater than tryptophan greater than histidine greater than lysine greater than other amino acids. Glycine, Tris and urea were ineffective competitors of p-MB inhibition. Double reciprocal plots showed that the Km for glucose-6-phosphate was increased and the Vmax reduced in the presence of p-MB. HgCl2 was a more effective inhibitor than p-MB with a Ki of 6 X 10(-6) M. We conclude that a reaction of p-MB with M2 sulfhydryls does not play a part in the inhibition of enzyme activity. It is suggested that p-MB may interact with one or more amino acid side chains in such a way that enzyme conformation is altered.
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PMID:The effect of p-hydroxymercuribenzoate and congeners on microsomal glucose-6-phosphatase. 18 75

Mercuric chloride was administered once i.p. to female Fischer-344 rats at doses of 0, 0.2, 0.6 and 1.8 mg/kg. Although there were no alterations in the urinary excretion of lactate dehydrogenase, significant elevations in the activities of urinary (U) alkaline phosphatase, glutamic-pyruvic transaminase (GPT) and glutamic-oxalacetic transaminase (GOT) indicated that mercuric chloride was nephrotoxic. There was no evidence of hepatotoxicity as hepatic glucose-6-phosphatase and serum sorbitol dehydrogenase were essentially unaffected by mercuric chloride administration. The activities of ethylmorphine demethylase, hexobarbital oxidase and aldrin epoxidase determined in vitro were not inhibited by mercuric chloride although aniline hydroxylase activity was decreased. Of the four phase-II reactions measured, only the glucuronidation of chloramphenicol was diminished by treatment with mercuric chloride. Results from the in vivo studies on the metabolism of lindane, which indicated no change in the excretion of free or conjugated metabolites, were in close agreement with the in vitro data suggesting that the nephrotoxic effects of mercuric chloride do not alter the urinary excretion of the model substrate lindane.
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PMID:A comparison of in vitro and in vivo methods for evaluating alterations in hepatic drug metabolism following mercuric chloride administration. 242 44

Alterations in the levels of selected enzymes have been studied in the liver, kidney and brain of mouse following mercuric chloride (1 mg/Kg body wt./d) administration for 10, 20 and 30 d. The activity of acid phosphatase increased in all the tissues, the highest increase was recorded in the kidneys which showed as much as 4.5 fold elevation following mercuric chloride administration for 30 d. Although the alkaline phosphatase activity in the liver and the brain increased following HgCl2 administration, the kidneys experienced a tremendous decline in this enzyme following the same treatment. Mercury-induced changes in ATPase were complex inasmuch as the nature and magnitude of these changes varied with the tissue as well as the duration of the treatment. Whereas the liver ATPase declined after all the treatment intervals, this enzyme increased in the kidney and brain following administration of HgCl2 for 10 d. However, both the kidneys and brain registered a substantial fall in ATPase activity when HgCl2 administration was continued for 30 d. The levels of both glucose-6-phosphatase and succinic dehydrogenase decreased in all the tissues following HgCl2 administration. Invariably, the magnitude of decrease was the highest after 30 d treatment with HgCl2.
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PMID:Enzyme changes in the brain, liver and kidney following repeated administration of mercuric chloride. 302 11

The effects of mercuric chloride intoxication on the activities of acid and alkaline phosphatases and glucose-6-phosphatase in the hepatopancreas of a freshwater prawn Macrobrachium lamarrei (H. Milne Edwards) were determined after 24, 48, 72, and 96 hr. Mercuric chloride intoxication resulted in elevation of acid phosphatase and inhibition of alkaline phosphatase activities, but glucose-6-phosphatase activity was elevated up to 72 hr after which (i.e., after 96 hr of exposure) inhibition in the enzyme activity was noted at two higher concentrations. Alterations in the activities of these enzymes after mercuric chloride intoxication have been shown to adversely affect the general metabolism of the freshwater prawn.
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PMID:Mercuric chloride intoxication in freshwater prawn. II. Effect on phosphatases activity. 609 12

The effectiveness of the antioxidant thiol, N-acetylcysteine (NAC), in enhancing methylmercury (CH3HgCl) excretion and its utility as a possible antidote in CH3HgCl poisoning has been reported. NAC, however, has been reported to be ineffective in accelerating excretion of divalent toxic metals, including inorganic mercury, Hg2+. In this study, we evaluated the possible protective effect of short-term pretreatment with NAC against mercuric chloride (HgCl2) toxicity in rat model. This is aimed at determining its chemopreventive or prophylactic benefit in situations of high risk exposure (occupational/industrial) to mercury. Rats were divided into three treatment groups. Group I received saline (10 ml/kg) and served as control. Group II received HgCl2 (5mg/kg) and group III received NAC (10mg/kg) plus (5mg/kg). All administration was via intraperitoneal (i.p.) injection. Saline and NAC were administered for 5days and HgCl2 was administered to rats in groups II and III on the 5th day. Animals were sacrificed 24 hours after HgCl2 injection and samples obtained for biochemical evaluation. Results revealed that single i.p. injection of HgCl2 induced significant renal oxidative damage resulting in significant decrease in the activities of superoxide dismutase (SOD), catalase (CAT), glutathione-s-transferase (GST), depletion of reduced glutathione (GSH) and increase in malondialdehyde (MDA) levels in these rats. The activities of glucose-6-phosphatase (G6Pase) and 5'-nucleotidase (5'-NTD) (markers of microsomal damage) also decreased in these HgCl2 treated rats. The oxidative damage induced by HgCl2 led to significant alterations in renal histology and caused functional impairment (indicated by elevated blood urea nitrogen (BUN) and serum creatinine) in these rats. NAC was effective in attenuating the oxidative damage, functional impairments and histopathological changes that characterized HgCl2 intoxication in this study. Renal antioxidant defense system was re-enforced by NAC, leading to increase in the activities of SOD, CAT, GST and decreases in GSH depletion and MDA level. Our results therefore reveal the ameliorative effect of NAC pretreatment against HgCl2 toxicity in vivo, thus, suggesting its usefulness as a possible chemoprophylactic agent during occupational or industrial exposure to inorganic mercury.
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PMID:N-acetylcysteine pretreatment ameliorates mercuric chloride-induced oxidative renal damage in rats. 2241 58