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At least 487 records · Page 27Linked to original sources
PubMed2000

Biosynthesis of cobalamin (vitamin B12): a bacterial conundrum.

The biosynthesis of cobalamin (vitamin B12) is described, revealing how the concerted action of around 30 enzyme-mediated steps results in the synthesis of one of Nature's most structurally complex 'small molecules'. The plethora of genome sequences has meant that bacteria capable of cobalamin synthesis can be easily identified and their biosynthetic genes compared. Whereas only a few years ago cobalamin synthesis was thought to occur by one of two routes, there are apparently a number of variations on these two pathways, where the major differences seem to be concerned with the process of ring contraction. A comparison of what is currently known about these pathways is presented. Finally, the process of cobalt chelation is discussed and the structure/function of the cobalt chelatase associated with the oxygen-independent pathway (CbiK) is described.

Aminolevulinic Acid↗
PubMed2001

High-valent corrole metal complexes.

This commentary concentrates on corrole complexes with the three metal ions that are most relevant to oxidation catalysis: chromium, manganese, and iron. Particular emphasis is devoted to the only recently introduced meso-triarylcorroles and a comparison with the traditionally investigated beta-pyrrole-substituted corroles. Based on a combination of spectroscopic methods, electrochemistry, and X-ray crystallography, it is concluded that in most high-valent metallocorroles the corrole is not oxidized. Both experimental (for (oxo)chromium(V) corrole) and computational (for (oxo)manganese(V) corrole) evidence indicate that the stabilization of high-valent metal ions by corroles originates from a combination of short metal-nitrogen bonds and large metal out-of-plane displacements in the corrole, which lead to quite unexpected interactions of the oxo-metal pi* orbitals with the in-plane orbitals of the corrole.

Corrinoids↗
PubMed1984

Biochemistry and clinical chemistry of vitamin B12 transport and the related diseases.

This review focusses on research performed by the author and coworkers. The absorption, turnover and excretion of cobalamin and the pathogenesis of cobalamin deficiency states are described and the laboratory tests used to diagnose these states are discussed. Topics dealt with in detail include: overall turnover, daily need, enterohepatic circulation and excretion of cobalamin and other corrins . The soluble proteins mediating cobalamin transport and their cellular receptors are described and their nomenclature, isolation, structure and mode of action, the role of calcium in the membrane transport, the evolution of these systems and the analogies with transport systems for other substrates are discussed together with deficiency states, especially fish tapeworm anemia and familial selective vitamin B12 malabsorption with proteinuria. Folate deficiency is a relatively rare cause of megaloblastic anemia in Scandinavia but common in North America and explanations for this difference are suggested. The methods of assaying cobalamin in serum and plasma and the performance of radiovitamin B12 absorption tests are critically evaluated. The measurement of intrinsic factor in gastric juice, serum, amniotic fluid and urine is described.

Anemia, Megaloblastic↗
PubMed1991

High-performance liquid chromatographic analysis of the (cyanoaquo) stereoisomers of several putative vitamin B12 precursors.

The cyanoaquo and aquocyano stereoisomers of several putative vitamin B12 precursors are reversibly formed and can be separated using analytical high-performance liquid chromatographic methods. The behavior of these stereoisomers varies somewhat depending on the type of column used and the chromatographic conditions employed. Both reversed-phase and ion-exchange columns can be used to observe the reversible formation and separation of the stereoisomers of (H2O,CN)cobyric acid, cobinamide and the cobinic acid pentaamide-1, -2 and -3 structural isomers. The greatest differences in retention times are seen when the pH of the eluting buffer is less than 4.0 and the buffer contains no KCN.

Chromatography, High Pressure Liquid↗