Polymorphism, cystathionine synthetase

Cystathionine /3-synthetase contains heme as well as pyridoxal phosphate, but this seems to have a regulatory rather than catalytic role the yeast enzyme does not contain heme (Jhee et al., 2000 Kabil et al., 2001). A common genetic polymorphism in human cystathionine /S-synthetase (a 68-base-pair insertion, occurring in about 12% of the general population) is associated with a lower than normal increase in plasma homocysteine after a methionine load in patients with low vitamin Be status, suggesting that the variant enzyme may have higher affinity for its cofactor than the normal form - the reverse of the position in the vitamin Bg responsive genetic diseases discussed in Section 9.4.3 (Tsaietal., 1999). 

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