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Biomedical subjects

A Bhaduri

Publications and source records attributed to A Bhaduri.

At least 55 records · Page 3Linked to original sources
PubMed1983

Characterization of pyridine nucleotide binding site of UDP-glucose 4-epimerase from Saccharomyces fragilis.

UDP-glucose 4-epimerase from Saccharomyces fragilis has 1 mol of NAD firmly bound per mol of the dimeric apoenzyme. This prevents a direct study of the coenzyme binding site of the protein. Dissociation of the dimer with p-chloromercuribenzoate and its reconstitution with exogenous NAD or one of its analogues and 2-mercaptoethanol provides an indirect method of study of the site. Depending on the reconstitution properties, the analogues can be classified in the following groups: (i) analogues that have no affinity for the site; (ii) analogues that have affinity but are not incorporated into the apoenzyme; (iii) analogues that produce catalytically inactive holoenzymes; and (iv) analogues that produce catalytically active holoenzymes. Minimum structural requirements that lead to affinity for the coenzyme site and to binding to the apoenzyme can also be discerned from these studies. Reconstitution with etheno-NAD, a fluorescent analogue of NAD, indicates the presence of a hydrophobic pocket for the adenosine subsite.

Binding Sites↗
PubMed1982

The presence of elements of a dinucleotide fold in UDP-glucose 4-epimerase from Saccharomyces fragilis.

UDPglucose 4-epimerase (EC 5.1.3.2) from Saccharomyces fragilis is a holoenzyme containing 1 mol NAD per mol dimeric protein. The enzyme can be dissociated with p-chloromercuribenzoate and can be reconstituted in the presence of 2-mercaptoethanol and exogenous NAD. Using Cibacron blue F3GA in this reconstituting system, competition between NAD and the dye for the pyridine nucleotide-binding site could be demonstrated. Inactive holoenzyme containing Cibacron blue can also be obtained under these conditions. These data suggest the possible presence of elements of a dinucleotide fold in this enzyme.

Anthracenes↗
PubMed1982

Simultaneous reconstitution of Escherichia coli membrane vesicles with D-lactate and D-amino acid dehydrogenases.

Purified preparations of D-amino acid dehydrogenase [Olsiewski, P.J., Kaczorowski, G. J., & Walsh, C. T. (1980) J. Biol. Chem. 225, 4487] and D-lactate dehydrogenase [Kohn, L.D., & Kaback, H.R. (1973) J. Biol. Chem. 248, 7012] bind independently to right-side-out and inverted Escherichia coli vesicles and to phosphatidylcholine liposomes without detectable competition. The reconstituted vesicles catalyze D-lactate- and D-alanine-dependent respiration (O2 uptake), proton translocation, and proton/lactose symport. The enzymes do not share common sites of association on either face of the E. coli membrane, and binding of both enzymes to the bilayer appears to be due to nonspecific affinity for the surface rather than specific binding to proteinaceous receptors. Each enzyme, however, appears to reduce a common proton translocating step in the membrane-bound respiratory chain, and substrate-derived electrons are transferred through a common rate-determining redox component that precedes the site of proton translocation. The results suggest that although binding is nonspecific, there is a common site for proton translocation in the membrane between the flavin-linked dehydrogenases and the cytochromes and that this site is accessible by distinct routes of electron transfer from primary dehydrogenases on either surface of the membrane.

Biological Transport↗
PubMed1980

Presence of two conformationally vicinal sulfhydryl groups at the active site of UDP-glucose 4-epimerase from Saccharomyces fragilis.

UDP-glucose 4-epimerase from Saccharomyces fragilis was inactivated by diazene dicarboxylic acid bis-N,N-dimethylamide or diamide, a compound that can specifically oxidize conformationally vicinal sulfhydryl groups on protein surfaces. The inactive enzyme was shown to retain the original dimeric structure and NAD, which is a coenzyme for this reaction, was not dissociated from the apoenzyme. The loss of activity was due to the direct modification of sulfhydryl groups and could not be attributed to any subsequent loss of structural integrity. The activity of the enzyme could be regained almost completely on incubation with mercaptoethanol alone and no exogenous NAD was needed for reactivation. The reactivated enzyme showed most of the characteristic properties of the native enzyme like activation by cations or inhibition by UMP. Presence of substrate provided partial protection against inactivation by the reagent. Formation of disulfide bond(s) across the subunits was demonstrated by sodium dodecyl sulfate gel electrophoresis in absence of mercaptoethanol. Titration of native and diamide-inactivated enzyme with p-chloromercuribenzoate revealed that only two sulfhydryl groups were involved in the formation of the disulfide cross-linkage across the subunits. The above results indicate the possible presence of two conformationally vicinal sulfhydryl groups at two different subunits of the enzyme that constitute part of the active site.

Binding Sites↗
PubMed1980

Fluorescence properties of reconstituted forms of UDP-glucose 4-epimerase from Saccharomyces fragilis.

UDP-glucose 4-epimerase from Saccharomyces fragilis exhibits a very characteristic intense fluorescence with an excitation maximum at 360 nm and an emission maximum at 433 nm. The fluorescence spectrum resembles the fluorescence of free NADH with an apparent blue shift and, although the exact nature of the fluorophore is not known, the protein-bound NAD, which is a coenzyme for this reaction, or its reduced form is obviously involved in the emission of the fluorescence. The fluorphore therefore constitutes part of the active site. The inactivation of epimerase with diazinedicarboxylic acid bis(N,N-diethylamide), a reaction shown in the previous paper to form a disulfide linkage across the subunits, results in a simultaneous and correlated loss of the characteristic fluorescence of the enzyme. Reaction with mercaptoethanol restores the native fluorescence with a 2 nm blue shift in emission maximum. These epxeriments provide additional evidence that the two conformationally vicinal sulfhydryl groups are located at the active site. Unlike the reconstituted enzyme obtained from the diamide-inactivated enzyme, the partialy active enzymes reconstituted from p-chloromercuribenzoate-inactivated and heat-inactivated enzymes fail to show the reappearance of the characteristic native fluorescence. Treatment with N-ethylmaleamide, on the other hand, leads to a form of the inactive enzyme that fully retains its fluorescent properties. A model depicting the minimal changes at the active site during the process of inactivation and reconstitution by these various treatments is presented.

Carbohydrate Epimerases↗