Linked Life Data

2405904

Source:http://linkedlifedata.com/resource/pubmed/id/2405904

Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
2
pubmed:dateCreated
1990-3-26
pubmed:abstractText
Cystathionine gamma-synthase catalyzes a pyridoxal phosphate dependent synthesis of cystathionine from O-succinyl-L-homoserine (OSHS) and L-cysteine via a gamma-replacement reaction. In the absence of L-cysteine, OSHS undergoes an enzyme-catalyzed, gamma-elimination reaction to form succinate, alpha-ketobutyrate, and ammonia. Since elimination of the gamma-substituent is necessary for both reactions, it is reasonable to assume that the replacement and elimination reaction pathways diverge from a common intermediate. Previously, this partitioning intermediate has been assigned to a highly conjugated alpha-iminovinylglycine quininoid (Johnston et al., 1979a). The experiments reported herein support an alternative assignment for the partitioning intermediate. We have examined the gamma-replacement and gamma-elimination reactions of cystathionine gamma-synthase via rapid-scanning stopped-flow and single-wavelength stopped-flow UV-visible spectroscopy. The gamma-elimination reaction is characterized by a rapid decrease in the amplitude of the enzyme internal aldimine spectral band at 422 nm with a concomitant appearance of a new species which absorbs in the 300-nm region. A 485-nm species subsequently accumulates in a much slower relaxation. The gamma-replacement reaction shows a red shift of the 422-nm peak to 425 nm which occurs in the experiment dead time (approximately 3 ms). This relaxation is followed by a decrease in absorbance at 425 nm that is tightly coupled to the appearance of a species which absorbs in the 300-nm region. Reaction of the substrate analogues L-alanine and L-allylglycine with cystathionine gamma-synthase results in bleaching of the 422-nm absorbance and the appearance of a 300-nm species. In the absence of L-cysteine, L-allylglycine undergoes facile proton exchange; in the presence of L-cysteine, L-allylglycine undergoes a gamma-replacement reaction to form a new amino acid, gamma-methylcystathionine. No long-wavelength-absorbing species accumulate during either of these reactions. These results establish that the partitioning intermediate is an alpha-imino beta,gamma-unsaturated pyridoxamine derivative with lambda max congruent to 300 nm and that the 485-nm species which accumulates in the elimination reaction is not on the replacement pathway.
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
http://linkedlifedata.com/resource/pubmed/chemical/Alanine, http://linkedlifedata.com/resource/pubmed/chemical/Allylglycine, http://linkedlifedata.com/resource/pubmed/chemical/Carbon-Oxygen Lyases, http://linkedlifedata.com/resource/pubmed/chemical/Cysteine, http://linkedlifedata.com/resource/pubmed/chemical/Fatty Acids, Monounsaturated, http://linkedlifedata.com/resource/pubmed/chemical/Homoserine, http://linkedlifedata.com/resource/pubmed/chemical/Lyases, http://linkedlifedata.com/resource/pubmed/chemical/O-succinylhomoserine, http://linkedlifedata.com/resource/pubmed/chemical/O-succinylhomoserine (thiol)-lyase, http://linkedlifedata.com/resource/pubmed/chemical/Pyridoxal Phosphate, http://linkedlifedata.com/resource/pubmed/chemical/Pyridoxamine, http://linkedlifedata.com/resource/pubmed/chemical/vinylglyoxylate
pubmed:status
MEDLINE
pubmed:month
Jan
pubmed:issn
0006-2960
pubmed:author
pubmed:issnType
Print
pubmed:day
16
pubmed:volume
29
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
442-51
pubmed:dateRevised
2006-11-15
pubmed:meshHeading
pubmed:year
1990
pubmed:articleTitle
Reaction mechanism of Escherichia coli cystathionine gamma-synthase: direct evidence for a pyridoxamine derivative of vinylglyoxylate as a key intermediate in pyridoxal phosphate dependent gamma-elimination and gamma-replacement reactions.
pubmed:affiliation
Department of Biochemistry, University of California, Riverside 92521.
pubmed:publicationType
Journal Article, Research Support, U.S. Gov't, Non-P.H.S.