Methionine, load test synthetase

Figure 9.5. Methionine load test for vitamin Be status. Methionine synthetase, EC 2.1.1.13 (vitamin Bi2-dependent) 2.1.1.5 (betaine as methyl donor) cystathionine synthetase, EC 4.2.1.22 and cystathionase, EC 4.4.1.1. Relative molecular masses (Mr) methionine, 149.2 homocysteine, 135.2 cystathionine, 222.3 and cysteine, 121.2.

The metabolism of methionine, shown in Figure 11.22, includes two pyridoxal phosphate-dependent steps cystathionine synthetase and cystathionase. Cystathionase activity falls markedly in vitamin deficiency, and as a result there is an increase in the urinary excretion of homocysteine and cystathionine, both after a loading dose of methionine and under basal conditions. However, as discussed below, homocysteine metabolism is affected more by folate status than by vitamin status, and, like the tryptophan load test, the methionine load test is probably not reliable as an index of... 

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See also in sourсe #XX -- [ , , , , ]

See also in sourсe #XX -- [ , , , , ]

See also in sourсe #XX -- [ , , , , ]

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