Transsulfuration depends on heme in addition to pyridoxal 5'-phosphate. Cystathionine beta-synthase is a heme protein

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 l...

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Bibliographic Details
Published in:The Journal of biological chemistry 1994-10, Vol.269 (41), p.25283-25288
Main Authors: Kery, V, Bukovska, G, Kraus, J P
Format: Article
Language:English
Subjects:
Animals
Cystathionine - biosynthesis
Cystathionine beta-Synthase - genetics
Cystathionine beta-Synthase - metabolism
Escherichia coli - metabolism
Heme - metabolism
Hemeproteins - genetics
Hemeproteins - metabolism
Homocysteine - metabolism
Humans
Kinetics
Liver - enzymology
Pyridoxal Phosphate - metabolism
Rats
Recombinant Proteins - metabolism
Serine - metabolism
Spectrophotometry
Sulfur - metabolism
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Summary: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.
ISSN:0021-9258
1083-351X
DOI:10.1016/S0021-9258(18)47244-4