cystathionine beta-synthase (serine sulfhydrase, beta-thionase, CBS)
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Function
- vitamin B6-dependent enzyme catalyzing the condensation of cysteine with serine to form cystathionine
- allosterically activated by adenosylmethionine (AdoMet)
- amino-acid biosynthesis; L-cysteine biosynthesis
- L-cysteine from L-homocysteine & L-serine: step 1/2
L-serine + L-homocysteine <--> L-cystathionine + H2O
Cofactor: pyridoxal phosphate
Structure
- homotetramer
- belongs to the cysteine synthase/cystathionine beta-synthase family
- contains 1 CBS domain
Compartment
Alternative splicing
named isoforms=2
Expression
- in adults, expressed in liver & pancreas > heart & brain > lung & kidney.
- in fetus, expressed in brain, liver & kidney
Pathology
- homozoygous defects in CBS are associated with homocystinuria
- heterozygous deficiency is prevalent in the US with a frequency of 1 in 300
- hyperhomocysteinemia results from heterozygous deficiency
Laboratory
More general terms
Additional terms
- cystathionine
- homocystinuria
- hyperhomocysteinemia
- methionine metabolism (trans-sulfuration pathway)
- pyridoxal phosphate
References
- ↑ Stryer Biochemistry WH Freeman & Co, New York,1988, pg 583-84
- ↑ Harrison's Principles of Internal Medicine, 14th ed. Fauci et al (eds), McGraw-Hill Inc. NY, 1998, pg 2199
- ↑ CBS mutation database http://www.uchsc.edu/cbs/cbsdata/cgidata.htm
- ↑ GeneReviews https://www.genecards.org/cgi-bin/carddisp.pl?gene=CBS
- ↑ UniProt http://www.uniprot.org/uniprot/P35520.html