Activity and kinetic characteristics of glutathione reductase in vitro in reverse micellar waterpool

The enzyme activity of glutathione reductase (NAD(P)H:oxidized-glutathione oxidoreductase, EC 1.6.4.2) incorporated in CTAB/H2O/CHCl3-isooctane (1:1, v/v) reverse micelles has been investigated. Enzyme follows the Michaelis-Menten kinetics within a specified concentration range. Effects of pH, waterpool (W0), and surfactant concentration on the activity of glutathione reductase have been studied in detail. Optimum pH for the maximum enzyme activity was found to be dependent on the size of the waterpool. Further, a substrate inhibition was observed when concentration of one of the substrates was present in large excess over the other substrate. Km values for the substrate, oxidized glutathione (GSSG) and NADPH in CTAB/H2O/CHCl3-isooctane (1:1, v/v) were determined at W0 values of 14.4, 20.0, 25.5 and 29.7, at pH 8.0. These values are close to those obtained in aqueous solution, whereas the kcat values vary with W0 values of 8.8 to 32.3. Studies on the storage stability in the reverse micelle at W0 29.7 and pH 8.0 showed that glutathione reductase retained about 80% of its activity even after a month. The enzyme showed a higher stability at high waterpool. Oxidized glutathione (GSSG) provides protection to glutathione reductase against denaturation on storage in reverse micellar solution. Apparently, the enzyme is able to acquire a suitable native conformation at waterpool 29.7 and pH 8.0 and thereby exhibits an activity and stability inside the micellar cavity that are almost equivalent to that in aqueous solution.     

Evidence for catalytic site cysteine and histidine by chemical modification of beta-hydroxy-beta-methylglutaryl-coenzyme A reductase

S-(4-Bromo-2,3-dioxobutyl)-coenzyme A inactivates both yeast and rat liver beta-hydroxy-beta-methylglutaryl-coenzyme A reductase. The inactivation is irreversible, complete in 15 s, and proportional to the concentration of the reagent. beta-Hydroxy-beta-methylglutaryl-CoA provides protection against inactivation, whereas NADPH does not. Inactivation is attributed to reaction with an essential cysteine at the beta-hydroxy-beta-methylglutaryl-CoA binding site. Experiments with other active site-directed reagents confirm the involvement of a cysteine and support the presence of an active-site histidine, but rule out the participation of arginine or serine.     

Effect of Centchroman (67/20) and 78/224 on nucleic acid and protein biosynthesis during implantation in rats

The biosynthesis of nucleic acids and proteins was studied in rat uterus by following the incorporation of [³H]-thymidine, [³H]-uridineand[¹⁴C]-leucinein control and pregnant rats in the presence and absence of two anti-implantation drugs. One of the drugs, 78/224 caused a significant increase in incorporation whereas the other drug, Centchroman, caused an inhibition in incorporation of all the three precursors. The implications of these changes in the light of estrogenicity, agonist and antagonist actions of anti-estrogens have been analysed. The importance of homeostatic mechanisms involved in nucleic acids and proteins for the maintenance of constant internal milieu for blastocyst attachment has been discussed.     

Fatty acid synthetase, malic enzyme and other NADP+ binding dehydrogenases have similar antigenic determinant(s) at the NADPH binding domain

The sequence of tryptic and chymotryptic peptides from cytosolic and mitochondrial rabbit liver serine hydroxymethyltransferase are compared to the proposed sequence of a protein coded for by the glyA gene of Escherichia coli. The E. coli glyA gene is believed to code for serine hydroxymethyltransferase. Extensive sequence homology between these peptides were found for the proposed E. coli enzyme in the aminoterminal two-thirds of the molecule. All three proteins have identical sequences from residue 222-231. This sequence is known to contain the lysyl residue which forms a Schiff's base with pyridoxal-P in the two rabbit liver enzymes. These results support the interpretation that the proposed sequence of E. coli serine hydroxymethyltransferase is correct. The data also show that cytosolic and mitochondrial serine hydroxymethyltransferase are homologous proteins.     

Fluidity,permeability and antioxidant behaviour of model membranes incorporated with α-tocopherol and vitamin E acetate

Magnetic resonance studies reveal a marked difference between the binding of α-tocopherol and that of the corresponding acetate (vitamin E acetate) with dipalmitoylphosphatidylcholine (DPPC) vesicles. This is reflected in differences in the phase-transition curves of the DPPC vesicles incorporated with the two compounds, as well as in the ¹³C relaxation times and line widths. A model for the incorporation of these molecules in lipid bilayers has been suggested. α-Tocopherol binds strongly with the lipids, possibly through a hydrogen bond formation between the hydroxyl group of the former and one of the oxygen atoms of the latter. The possibility of such a hydrogen bond formation is excluded in vitamin E acetate, which binds loosely through the normal hydrophobic interaction. The model for lipid-vitamin interaction explains the in vitro decomposition of H₂O₂ by α-tocopherol. α-Tocopherol in conjuction with H₂O₂ can also act as a free-radical scavenger in the lipid phase. The incorporation of α-tocopherol and vitamin E acetate in DPPC vesicles enhances the permeability of lipid bilayers for small molecules such as sodium ascorbate.     

Modification of supported lipid membranes by atomic force microscopy

The atomic force microscope (AFM) was used to structurally modify supported lipid bilayers in a controlled quantitative manner. By increasing the force applied by the AFM tip, lipid was removed from the scanned area, leaving a cut through the lipid bilayer. Cuts were repaired with the AFM by scanning the region with a controlled force and driving lipid back into the cut. A slow self-annealing of cuts was also observed.     

Efficacy of methyl 5(6)-(alpha-hydroxyphenylmethyl) benzimidazole-2-carbamate, a metabolite of mebendazole, against developing forms of experimental helminth parasites.

Methyl 5(6)-(alpha-hydroxyphenylmethyl) benzimidazole-2- carbamate, a metabolite of mebendazole, was evaluated against metamorphic forms of Ancylostoma ceylanicum in hamsters, Nippostrongylus brasiliensis in rats and cysticercoids of Hymenolepis nana in grain beetles. The test compound offered better action than mebendazole except against H. nana cysticercoids where the activity of the compound and mebendazole was comparable, but was inferior to the standard cestodicidal drug, praziquantel. The results suggest that the action was better by ip route compared to per os route of drug administration.     

Modulatory effects of metanil yellow on immunity in rodents.

Pathomorphological and immunological studies were carried out on rodents following oral administration of 0, 0.1, 0.25 and 0.5% (w/w) metanil yellow, mixed in diet, for 30 days. No significant change in hematologic parameters and histologic architecture of liver, kidney, mesenteric lymph node, thymus and urinary bladder was observed except for mild desquamation of intestinal villi and moderate changes in Peyer's patches of small intestine with higher doses. Among immunological parameters, significant enhancement in the primary humoral immune response (anti-SRBC IgM plaque forming cells of spleen) was observed with the lowest dose of metanil yellow while higher doses produced opposing effects. An elevated cutaneous delayed type hypersensitivity (DTH) reaction to SRBC was seen in 0.1% metanil yellow treated animals but higher doses did not influence the reaction. The treatment also caused changes in functional capabilities of macrophages. Although these immune alterations could hardly influence the local immunity of gut, as measured by the capacity of animals to cause rejection of Nippostrongylus brasiliensis parasite, the potential to modulate the immunity in general by metanil yellow however assumes considerable biological significance.     

Glucose oxidase immobilized electrode for potentiometric estimation of glucose

Glucose oxidase has been immobilized onto a thin platinum strip, by co-crosslinking with bovine serum albumin and glutaraldehyde. The retention of redox characteristics of glucose oxidase has been verified by cyclic voltammetry. The activity of the immobilized enzyme reduces to a quarter of its value when the enzyme is in solution but improves when coimmobilized with 1 urea. The potentiometric response builds up and remains stable after 100 s. It is sensitive to the thickness of the immobilizing matrix, pH and temperature. An improvement in the performance of the electrode has been achieved by coimmobilizing 2 urea and metal ions such as Mg²⁺ and Mn²⁺. The presence of Cu has been proved to be detrimental. The electrode has been calibrated in the 0.1–5.0 mM glucose concentration range. It gives a stable response for more than 50 independent assays and can be stored for 60 days without significant loss of function.     

Exoprotease production by sporogenous and asporogenous mycobacillin non-producer mutants ofBacillus subtilis

Mycobacillin non-producers, whether sporogenous or asporogenous, possess less exoprotease, but effective exoprotease producers are not always good mycobacillin yielders. There might exist a minimum level of exoprotease formation for elaboration of mycobacillin.