Homocysteine transmethylase

Hill et al. (141) hrst observed that light-stable yellow alkylcorrinoids could be synthesized. When methylcobalamin was treated with picrate, a yellow corrinoid was isolated which was shown to be stable to light, but unstable to cyanide. Similarly, Taylor and Weissbach (67) demonstrated that the methylcorrinoid-enzyme complex of N5-methyl-tetrahydro-folate-homocysteine transmethylase was stable to light, but isolation of... 

The related cobalt cofactor vitamin B12 (8), the coenzyme of methyl-malonyl CoA mutase and homocysteine transmethylase, contains a... 

Whitfield, C. D., and Weissback, H., Binding of snbstrate to N -methyl-tetrahydrop-teroyltriglutamate-homocysteine transmethylase. Biochem. Biophys. Res. Commun. 33, 996-1003 (1968). 

Turner, J.E. and S.K. Shapiro 5-Methylmethionine and 5-adenosyhnethionine-homocysteine transmethylase in higher plant seeds Biochem. Biophys. Acta 51 (1961) 581-584. 

The demonstration by Phillips and Laiigdon (1956) that the level of TPNH-cytochromc c reductase is increased in the livers of hyperthyroid rats and reduced in those of hypothyroid animals is of particular interest. Since the activity of this enzyme results in the production of triphospho-pyridiiie nucleotide (TPN), a cofactor required for many oxidative enzymes, this change is probably a direct reflection of the general over-all acceleration of oxidative processes, and, more specifically, of those which are TPN-linked. Decreased activity of lactic dehydrogenase (Vcstling and Knocpfelmacher, 1950) is compatible with the demonstrated ability of thyroxine to inhibit this enzyme in vitro (Wolff and Wolff, 1957 Radsma et al., 1957). Decreases in the in vivo activity of such enzymes as tyrosine oxidase, DOPA-decarboxylase, betaine-homocysteine transmethylase, and... 

Draper et al. (101) described an assay for /Vs-methyltetrahydrofolate-homocysteine transmethylase activity using instant TLC which permits the simultaneous determination of the newly synthesized methionine as well as the residual /Vs-methyltetrahydrofolate. 

Dubnoff and Borsook have demonstrated synthesis of methionine by liver and kidney preparations, and have separated a dimethylthetin transmethylase from betaine transmethylase. The dimethylthetin enzyme, renamed dimethylthetin-homocysteine methylpherase has been purified by Durell and Anderson, who suggest that their prepara-... 

The conversion of homocysteine to methionine requires a containing transmethylase. In the process THF is regenerated. Since methionine is available from other sources (diet, salvage amino acid pools) it is thought that the importance of this reaction lies not in the synthesis of the amino acid but in the regeneration of THF,... 

---