摘要:

The aqueous chemistry of vanadate (vanadium(V)) is very complex since many protonation equilibria and oligomerization equilibria are occurring simultaneously. Vanadate monomer (V1), dimer (V2), tetramer (V4) and pentamer (V5) are exchanging with each other on a millisecond time scale so that none of these species can be isolated for aqueous biological studies. Measuring the effects of each anion on an enzyme must be carried out in an equilibrium mixture containing the other vanadate oligomers. Defining conditions to measure the effects of oxovanadates is non-trivial, since vanadate interacts with buffers and other assay components. Information concerning the simple aqueous chemistry of vanadate with various ligands is thus necessary to ensure that the vanadate is free to interact with an enzyme or a protein. Experimental approaches, which take into account the aqueous chemistry of labile oxovanadates, to biological studies are described here. For this purpose, the interactions of oxovanadates with proteins and other protein-like ligands are considered briefly. The chemistry and approaches described here form the basis for an analysis of the interactions of vanadate oxoanions with proteins.

ISSN:0260-3594    

DOI:10.1080/02603599408035850

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Aqueous solutions of vanadate contain several labile oxovanadates; each interacts differently with enzymes and other proteins. Vanadate monomer, V1can act as a ground state or transition state analog of phosphate. Vanadate dimer, V2inhibits a series of enzymes including dehydrogenases, one aldolase and a phosphatase. V2can also activate enzymes, and this activation has been observed with a mutase and dehydrogenase. Vanadate tetramer, V4(often referred to as “metavanadate”), inhibits a large number of enzymes including dehydrogenases, isomerases, and one aldolase. V4also binds to a series of enzymes including superoxide dismutase, myosin and possibly adenylate kinase. V4has been identified as the species responsible for the specific UV-light induced photocleavage of the active site of myosin and possibly adenylate kinase. Redox chemistry between V1and V4and proteins has been reported. Vanadate pentamer, V5has not yet shown high affinity for proteins, and studies with related oxomolybdates show that a tetramer interacts more potently with the proteins than the pentamer. Vanadate decamer, V10is a less labile oxometalate that also inhibits and binds to proteins. The potent antiviral and anti-HIV activity of several oxometalates have increased the interest in protein interactions with large polyoxoanions. It is reasonable to expect that proteins catalyzing reactions of large anionic substrates (polymeric nucleic acids) tend to show high affinity for large polyoxometalates. The fact that other proteins, including cytochromecphosphorylase, phosphatases, dehydrogenases and an aldolase, also show affinity for these large polyoxometalates is perhaps more intriguing: this affinity suggests that some sequences and three dimensional arrays might favor binding of oxometalates.

ISSN:0260-3594    

DOI:10.1080/02603599408035851

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The nucleic acids RNA and DNA consist of nucleoside building blocks joined by phosphodiester linkages. Phosphodiesters are generally inert to hydrolytic cleavage under physiological conditions because their negative charge disfavors nucleophilic attack. However, the hydrolytic scission of phosphodiester linkages is an important and common biological process, and can occur rapidly in the presence of appropriate catalysts such as ribozymes and nuclease enzymes. Metals play an important role in this process. Several possible modes of action can be invoked for metal-promoted phosphate ester hydrolysis, including Lewis acid catalysis, Brønsted base catalysis by metal-bound hydroxides, nucleophilic catalysis by metal-bound hydroxides, Brønsted acid catalysis by metal-bound water, and electrostatic stabilization of transition states by positively charged metal ions. Here we critically discuss the roles of metals in the hydrolytic cleavage of nucleic acids and related model substrates.

ISSN:0260-3594    

DOI:10.1080/02603599408035852

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The topic discussed in this article is the synthesis of cationic complexes of plati-num(I1) containing η2−olefins, their reaction with nucleophiles, and the cleavage, under acidic conditions, of the platinum-carbon bond of the addition productsobtained therefrom. Some general features related to the electrotl distribution and bonding, the structural and conformational preferences, the reaction mechanisms and reactivity are discussed.

ISSN:0260-3594    

DOI:10.1080/02603599408035853

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

This is a scanned image of the original Editorial Board page(s) for this issue.

ISSN:0260-3594    

DOI:10.1080/02603599408035849

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor