Advances in Human Genetics 6 by Leon E. Rosenberg (auth.), Harry Harris, Kurt Hirschhorn PDF

By Leon E. Rosenberg (auth.), Harry Harris, Kurt Hirschhorn (eds.)

ISBN-10: 1461582644

ISBN-13: 9781461582649

ISBN-10: 1461582660

ISBN-13: 9781461582663

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Likewise, Tada et al. 158 ,159 showed that the defective kynureninase activity found in liver of patients with pyridoxine-responsive xanthurenic aciduria was restored to nearly normal values with in vitro addition of saturating amounts of PLP. These results indicate that such patients synthesize a mutant apoenzyme whose interaction with coenzyme is impaired either because the apoprotein has a reduced affinity for coenzyme or because its rate of binding to coenzyme is slowed. 98 The fact that nearly full holoenzyme activity is restored by PLP in vitro, however, implies that 44 Leon E.

That class of mutant (designated chi B) in which Ado-Cbl formation is blocked in both intact and broken cells is presumed to have a defect either in the second cobalamin reductase or in the adenosyltransferase enzyme noted in Fig. 4. In contrast, that class which is unable to synthesize Ado-Cbl in whole cells but which can synthesize this coenzyme normally in cell-free extracts (chi A) very likely has an abnormality of the first cobalamin reductase or of some as yet undefined intracellular transport step required for Ado-Cbl synthesis.

4) also exist in these normal human cells. 89 Since methylmalonyl-CoA mutase, the apoenzyme which requires Ado-Cbl for activity, is thought to be a mitochondrial protein, 55 whereas the methyitransferase apoenzyme appears to be cytoplasmic,168 it is obvious that complete understanding of intracellular cobalamin metabolism must also include knowledge of the subcellular transport and organellar localization of the vitamin and its coenzyme forms. 115 have proposed that cobalamin bound to TC II enters cells by a series of steps which include adsorption to membrane receptors, endocytosis of intact TC 11Cbl, formation of a secondary lysosomal vacuole in which the Cbl is split from TC II, and entry of Cbl into the mitochondrion (Fig.

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Advances in Human Genetics 6 by Leon E. Rosenberg (auth.), Harry Harris, Kurt Hirschhorn (eds.)

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