type	Journal Article
authors	Kery, V.; Bukovska, G.; Kraus, J. P.
title	Transsulfuration depends on heme in addition to pyridoxal 5'-phosphate. Cystathionine beta-synthase is a heme protein
journal	J Biol Chem
Activity	4.2.1.22
ui	95014316
year	(1994)
volume	269
number	41
pages	25283-8.
keywords	Animal
abstract	The first committed step of transsulfuration is catalyzed by cystathionine beta-synthase (CBS), a known pyridoxal 5'-phosphate (PLP) enzyme. The inferred amino acid sequences of rat liver CBS and rat liver hemoprotein H-450 are identical. We now confirm the presence of heme b in rat and human liver CBS. Heme almost entirely accounts for the visible spectrum of CBS rather than PLP. Human CBS, expressed in Escherichia coli, acquires heme b from the host bacteria. delta- Aminolevulinate supplementation during bacterial growth increases both the heme saturation and the specific activity of the homogeneous enzyme more than 3-fold. 1 mol of the 63-kDa CBS subunit binds 1 mol of each (heme and PLP). The presence of heme is required for PLP binding, and the amount of PLP bound is limited by the heme content. Removal of PLP, but not heme, from CBS is reversible. These findings suggest that heme is functionally incorporated into CBS only during protein folding. This report describes the first instance of an enzyme that depends upon both heme and PLP for its function.
last changed	2002/11/12 16:17