Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:4.2.1.22 (cystathionine beta-synthase)
 965 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We recently expressed human cystathionine beta-synthase (CBS) in Escherichia coli and purified it to homogeneity. We showed that CBS requires heme in addition to pyridoxal 5'-phosphate for its function. Previously, CBS, only about 20% saturated with heme, was purified from transformed bacteria. In the present study, we supplemented the bacteria with 0.3 mM delta-aminolevulinate (delta ALA), a precursor of heme. While growth of the bacteria did not change, a 50-fold elevation of the heme content per milligram of total protein was observed in the cell extracts of delta ALA-supplemented cells. The increase in heme biosynthesis depended on the overexpression of a heme acceptor--CBS. Our data suggest that bacterial heme synthesis is regulated beyond delta ALA synthase. The delta ALA treatment resulted in 8 times more total CBS activity with a 3.5-fold higher yield of the purified recombinant enzyme, more than 68% saturated with heme. Increased yield, higher specific activity, and improved heme saturation of CBS will facilitate large-scale preparation of the enzyme. This method should be applicable to the overexpression of other recombinant heme proteins in bacteria.
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PMID:Delta-aminolevulinate increases heme saturation and yield of human cystathionine beta-synthase expressed in Escherichia coli. 784 Jun 23

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.
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PMID:Transsulfuration depends on heme in addition to pyridoxal 5'-phosphate. Cystathionine beta-synthase is a heme protein. 792 20