Vinod K. Shah

Bio: Vinod K. Shah is an academic researcher from University of Wisconsin-Madison. The author has contributed to research in topics: Azotobacter vinelandii & Nitrogenase. The author has an hindex of 40, co-authored 82 publications receiving 4695 citations.

Isolation of an iron-molybdenum cofactor from nitrogenase

Abstract: A method for the isolation of an iron-molybdenum cofactor (FeMoCo) from component I of nitrogenase is described. This method is used to isolate FeMoCo from aerobic, anaerobic, facultative, and photosynthetic nitrogen-fixing organisms. The Fe/Mo ratio in the FeMoCo from Azotobacter vinelandii and Clostridium pasteurianum is 8:1. The FeMoCo contains six atoms of acid-labile sulfide per eight Fe atoms. Crystalline component I from A. vinelandii contains 2 Mo, 33 Fe, and 27 acid-labile sulfide atoms per molecular weight of 250,000. The specific activity of FeMoCo is 425 nmol of C(2)H(4) formed/min per nmol of Mo. There is better than 98% reconstitution between FeMoCo and inactive component I in A. vinelandii mutant strain UW45. The FeMoCo yield from component I is about 90%. FeMoCo from nitrogenase component I of C. pasteurianum, Klebsiella pneumoniae, Bacillus polymyxa, and Rhodospirillum rubrum activates inactive component I in an extract from mutant strain UW45 and follows saturation kinetics. The FeMoCo in various nitrogen-fixing organisms seems to be very similar. Wild-type A. vinelandii derepressed for nitrogenase synthesis in tungsten-containing medium and K. pneumoniae mutant strain UN109 are also activated in vitro by FeMoCo. The FeMoCo is very sensitive to oxygen, but is stable even at room temperature as long as it is kept anaerobic and in N-methylformamide, the solvent used for its isolation. FeMoCo is unstable in an aqueous environment, even though it is kept strictly anaerobic. Knowledge of the structure of this cofactor should be useful for understanding the role of molybdenum at the active site of nitrogenase, role of ligands close to molybdenum in electron and proton transfer, and the catalytic mechanism of nitrogen fixation. The FeMoCo might be used as a model for synthesizing catalysts for chemical nitrogen fixation.

Microbial heavy-metal resistance

Abstract: We are just beginning to understand the metabolism of heavy metals and to use their metabolic functions in biotechnology, although heavy metals comprise the major part of the elements in the periodic table. Because they can form complex compounds, some heavy metal ions are essential trace elements, but, essential or not, most heavy metals are toxic at higher concentrations. This review describes the workings of known metal-resistance systems in microorganisms. After an account of the basic principles of homoeostasis for all heavy-metal ions, the transport of the 17 most important (heavy metal) elements is compared.

Structural and Functional Aspects of Metal Sites in Biology

Abstract: For present purposes, a protein-bound metal site consists of one or more metal ions and all protein side chain and exogenous bridging and terminal ligands that define the first coordination sphere of each metal ion. Such sites can be classified into five basic types with the indicated functions: (1) structural -- configuration (in part) of protein tertiary and/or quaternary structure; (2) storage -- uptake, binding, and release of metals in soluble form: (3) electron transfer -- uptake, release, and storage of electrons; (4) dioxygen binding -- metal-O{sub 2} coordination and decoordination; and (5) catalytic -- substrate binding, activation, and turnover. The authors present here a classification and structure/function analysis of native metal sites based on these functions, where 5 is an extensive class subdivided by the type of reaction catalyzed. Within this purview, coverage of the various site types is extensive, but not exhaustive. The purpose of this exposition is to present examples of all types of sites and to relate, insofar as is currently feasible, the structure and function of selected types. The authors largely confine their considerations to the sites themselves, with due recognition that these site features are coupled to protein structure at all levels. In themore » next section, the coordination chemistry of metalloprotein sites and the unique properties of a protein as a ligand are briefly summarized. Structure/function relationships are systematically explored and tabulations of structurally defined sites presented. Finally, future directions in bioinorganic research in the context of metal site chemistry are considered. 620 refs.« less

Biological Nitrogen Fixation

Abstract: Biological nitrogen fixation (BNF) is the process of the reduction of dinitrogen from the air to ammonia carried out by a large number of species of free-living and symbiotic microbes called diazotrophs. BNF presents an inexpensive and environmentally sound, sustainable approach to crop production and constitutes one of the most important Plant Growth Promotion (PGP) scenarios. Here I will summarize various aspects of BNF, including the dinitrogen reduction catalysed reaction carried out by “nitrogenase” and the enzymes/genes involved and their regulation, the inherent “oxygen paradox” , the identification of diazotrophs, sustainable agricultural uses of BNF, symbiotic plant-diazotroph interactions and endophytic diazotrophs, data from the field, and future prospects in BNF.

Extended x-ray absorption fine structure—its strengths and limitations as a structural tool

Abstract: The authors review the development of extended x-ray absorption fine structure (EXAFS) within the last decade. Advances in experimental techniques have been largely stimulated by the availability of synchrotron radiation. The theory of EXAFS has also matured to the point where quantitative comparison with experiments can be made. The authors review in some detail the analysis of EXAFS data, starting from the treatment of raw data to the extraction of distances and amplitude information, and they also discuss selected examples of applications of EXAFS chosen to illustrate both the strength and limitations of EXAFS as a structural tool.