W. G. Hodgson

Bio: W. G. Hodgson is an academic researcher from American Cyanamid. The author has contributed to research in topics: Molybdenum. The author has an hindex of 1, co-authored 1 publications receiving 61 citations.

Structural and metabolic relationship between the molybdenum cofactor and urothione.

Abstract: The molybdenum cofactor isolated from sulfite oxidase (sulfite: ferricytochrome c oxidoreductase, EC 1.8.2.1) and xanthine dehydrogenase (xanthine:NAD+ oxidoreductase, EC 1.2.1.37) in the presence of iodine and KI (form A) has been shown to contain a pterin nucleus with an unidentified substituent in the 6 position [Johnson, J. L., Hainline, B. E. & Rajagopalan, K. V. (1980) J. Biol. Chem. 255, 1783-1786]. A second inactive form of the cofactor was isolated aerobically but in the absence of iodine and KI. The latter cofactor derivative (form B) is highly fluorescent, has a visible absorption band at 395 nm and, like form A, contains a phosphate group. Cleavage of the phosphate ester bond with alkaline phosphatase exposes a glycol function that is sensitive to periodate. Oxidation of form B with alkaline permanganate yields a highly polar compound with properties of a sulfonic acid, suggesting that the active molybdenum cofactor might contain sulfur. The sulfur-containing pterin urothione characterized by Goto et al. [Goto, M., Sakurai, A., Ohta, K. & Yamakami, H. (1969) J. Biochem. 65, 611-620] had been isolated from human urine. The permanganate oxidation product of urothione, characterized by Goto et al. as pterin-6-carboxylic-7-sulfonic acid, is identical to that obtained from form B. Because urothione also contains a periodate-sensitive glycol substituent, a structural relationship is suggested. The finding that urine samples from patients deficient in the molybdenum cofactor are devoid of urothione demonstrates a metabolic link between the two molecules.

6 Molybdenum Iron-Sulfur Flauin Hydroxylases and Related Enzymes

Abstract: Publisher Summary This chapter describes the enzymes, xanthine oxidase, xanthine dehydrogenase, aldehyde oxidase, and sulfite oxidase. In addition to the molybdenum hydroxylases, sulfite oxidase is discussed in this chapter, though it contains heme rather than flavin and no iron-sulfur. This is because it contains molybdenum, apparently in a chemical environment within the active center, which is quite like that of the metal in the other enzymes. The term xanthine oxidase is to be taken to refer to the enzyme from milk. The enzymes to be considered are widely distributed. Thus, one or more molybdenum hydroxylases have been found in organisms as different in complexity as man and bacteria. In mammal's oxidation of hypoxanthine to xanthine and of xanthine to uric acid are steps in purine catabolism prior to excretion, uric acid being the end product in primates. Individual humans, genetically deficient in xanthine oxidase, are apparently little the worse for the deficiency. The reduced oxygen derivatives are supposed to be available for coupled oxidation reactions—for example, in drug catabolism. The most obvious objection to this hypothesis is the conclusion, discussed in the chapter, that the dehydrogenase form of the xanthine-oxidizing enzymes is more native than is the oxidase form. It must be conceded that the true role of the enzymes in humans and many other species remains somewhat problematical.

Bioinorganic chemistry of pterin-containing molybdenum and tungsten enzymes

Abstract: Publisher Summary This chapter presents a discussion on the bioinorganic chemistry of pterin-containing molybdenum and tungsten enzymes. The chapter focuses on the current results and the interplay of model and enzyme chemistry. Attention is directed to sulfite oxidase and xanthine oxidase, the archetypal examples of molybdenum enzymes, containing, respectively, dioxo-Mo(VI) and oxo-thio-Mo(VI) oxidized centers. Biochemical and model studies of molybdopterin, Mo-co, and related species are described in this chapter. A brief survey on the physical and spectroscopic techniques employed in the study of the enzymes is presented and their impact on the current understanding of the coordination about the molybdenum atom in sulfite oxidase and xanthine oxidase is discussed. Structural and spectroscopic models are also presented in the chapter. The chapter also explains the xanthine oxidase cycle and facets of intramolecular electron transfer in molybdenum enzymes. The pterin-containing tungsten enzymes and the evolving model chemistry are discussed. Current descriptions of the coordination environment of the molybdenum centers of the enzymes rest primarily upon the comparisons of the spectra of the enzymes with the spectra of well-characterized molybdenum complexes. The unexpected discovery that several hyperthermophilic organisms possess pterin-containing tungsten enzymes promises to stimulate the development of oxo-thio-tungsten chemistry.

The inorganic biochemistry of molybdoenzymes.

Abstract: Molybednum-containing enzymes (Coughlan, 1980; Spiro, 1985) occupy a significant place in the development of the field now termed inorganic biochemistry. The importance of the metal as a biological trace element depends on its involvement in the known, and perhaps other as yet unknown, molybdoenzymes. That it plays a role in biological nitrogen fixation, the process whereby the enzyme nitrogenase in the root nodules of plants converts atmospheric nitrogen into ammonia, was recognized in the 1930s. The metal is also a constituent of a variety of other enzymes, having first been found in a mammalian enzyme, xanthine oxidase, in the 1950s.