Molybdenum atomic weight

The element molybdenum (atomic weight 95.95) constitutes 0.08% of the weight of nitrate reductase. If the molecular weight of nitrate reductase is 240,000, what is its likely quaternary structure ... 

Table 1. Some molybdenum-containing enzymes. For some of the enzymes the numerical data are rather approximate only. Turnover numbers refer to temperatures between 23 and 30°. Since some of the molecular weights are particularly uncertain, contents of flavin etc. are expressed per molybdenum atom rather than per mole of protein. Most of the enzymes have a much wider range of substrate specificities than has been indicated...

Crouch AC, Tulpin TA (1964) Isotopic composition and the atomic weight of naturally occurring molybdenum ... 

Lee DC, Halliday AN (1995) Precise determinations of the isotopic compositions and atomic weights of molybdenum, tellurium, tin and tungsten using ICP magnetic-sector multiple collector mass-spectrometry. Int J Mass Spectr Ion Proc 146 35-46... 

Lu Q, Masuda A (1994) The isotopic composition and atomic-weight or molybdenum, hit J Mass Spectr Ion Proc 130 65-72... 

The inhibition of enzyme systems dues nut necessarily cause unwarned effects. Consider the enzyme xanthine oxidase. It contains two atoms of molybdenum, four Fe2S2, and two FAD (flavin adenine dinucleotidei moieties, and it has a molecular weight of 275.000-300.000. There is no evidence that the two units (Mo/SFe Sj/FAD) are near each other or interact in any way. It is believed that the immediate environment of each molybdenum atom consists of one oxygen and three sulfur atoms (additional ligands may be present) 12... 

The most appropriate position for ruthenium in the Periodic Table is as the first member of the second series of horizontal triads. Hence its atomic weight should lie between that of molybdenum (96) and rhodium (102-9), but nearer in point of magnitude to the last named since an element should be in Group VII between it and molybdenum, but has yet to be discovered. 

Molybdenum is the element of atomic number 42, and its atomic weight is 95.95. It is a shiny grey metal, resembling steel in appearance, but with an unusually high melting point of 2610 C. It has seven known natural stable isotopes whose mass numbers are 98, 96, 92, 95, 100, 97 and 94 in decreasing order of abundance. It was first isolated by P.J. Hjelm in 1782 from molybdenite, which he converted to oxide and then reduced by heating with charcoal ... 

The MoFe-protein is an a2 2 tetramer (with the subunits coded by the nifD and nifK genes, respectively), with a total molecular weight of 240,000. The two subunits are of similar size for example, the isolated a and /3 subunits of A. vinelandii MoFe-protein have 491 and 522 amino acids, respectively (46). In general, the amino acid sequences of MoFe-proteins are less well conserved than are Fe-protein sequences, so that the MoFe-protein sequences from A. vinelandii and C. pasteuria-num are only 36% identical (47). Associated with the MoFe-protein tetramer are approximately 2 molybdenum atoms, 30 iron atoms, and 30 sulfur atoms that are organized into two types of metal centers the FeMo-cofactor and the P-cluster pair. The structures and properties of these centers have been extensively probed by a wide variety of techniques. 

Atomic Weight.—For reasons similar to those applying in the case of chromium (p. 16), the atomic %veight of molybdenum is three times the equivalent of the metal in the molybdic salts, or six times that in the molybdates. Molybdenum may be di-, tri-, or hexa-valent. 

The results of investigations concerning the atomic weight of molybdenum are as follows ... 

The determinations made before 1858 may be ignored as of no modern significance. Those made since that date yield three ratios, from which the atomic weight of molybdenum may be calculated, namely ... 

Atomic Weight.— Like chromium and molybdenum, tungsten may in its compounds be di-, tri-, or hexa-valent from a consideration of its specific heat, the isomorphism of its compounds, its position in the... 

In 1872 Mendeleeft pointed out that there was no place in the Periodic Table for a trivalent element of atomic weight 120, and drew attention to the similarity of uranium to chromium, molybdenum, and tungsten he therefore suggested that the atomic weight should be doubled, so that uranium could be placed below these elements in the table. He also formulated the oxides, by analog with those of the other elements in the group, as follows uranous oxide UOg, urano-... 

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