Deaminases serine deaminase

L-Serine dehydratase [EC 4.2.1.13], also known as serine deaminase and L-hydroxyaminoacid dehydratase, catalyzes the pyridoxal-phosphate-dependent hydrolysis of L-serine to produce pyruvate, ammonia, and water. In a number of organisms, this reaction is also catalyzed by threonine dehydratase. 

SERINE DEHYDRATASE SERINE DEHYDROGENASE SERINE HYDROXYMETHYLTRANSFERASE SERINE PALMITOYLTRANSFERASE Serine deaminase... 

L-Serine is converted to pyruvate + NH3 by serine dehydratase (deaminase) in a PLP-dependent reaction. However, using the same coenzyme selenocysteine is converted by selenocysteine lyase into L-alanine + elemental selenium Se°. l-Cysteine may be converted by PLP-dependent enzymes into wither H2S or into S° for transfer into metal clusters. Compare the chemical mecha-... 

D- and L- Serine dehydratases (deaminases) Tryptophan indole-lyase (tryptophanase) Tyrosine phenol-lyase ... 

Both the l- and D-serine deaminase catalyze the elimination of the amino functionality of both l- and D-serine, but the mechanism proceeds via the initial elimination of water and these enzymes are thus classified as hydrolyases (l- and D-serine dehydratases E.C. 4.2.1.13 and E.C. 4.2.1.14, respectively)[27, 28. The aminoacrylate generated is unstable and subsequent elimination of the amine results in the formation of pyruvate. Similarly, threonine deaminase is in effect a dehydratase that converts L-threonine into 2-oxobuturate, water and ammonia (E.C. 4.2.1.16) (Scheme 12.6-1). 

Taka amylase a bacterial a-amylase (EC 3.2.1.1) isolated and crystallized from Aspergillus oryzae taka diastase preparations. T. a. (Af, 50,000) is a calcium-containing, single-chain protein with V-terminal alanine and C-terminal serine. Like the tetrameric Bacillus subtilis a-amylase (Af, 96,000), T.a. is resistant to sodium dodecylsulfate but is reversibly denatured by 6 M guanidine or 8 M urea. T.a. must not be confused with Adenosine deaminase (see), which is also present in taka diastase. 

Enzymes which show the repression effect include enzymes of glycerol regulation, tryptophanase, D-serine deaminase, histidase, the o/operon, and the lac operon. As far as is known, all the enzymes classified as inducible show the effect. 

While this work was proceeding, Yanofsky and Reissig independently found the L-serine deaminase of Neurospora This enzyme is activated by pyridoxal phosphate, and is not stimulated by ATP, biotin, or glutathione. The Neurospora enzyme is somewhat more active with threonine than with serine, and acts only on the L-isomers. 

A purified preparation of homoserine deaminase from rat liver was found by Binkley and Olson" not to attack serine or threonine. The latter finding would appear to rule out the possibility that threonine is an intermediate in reaction 19. Although some activation by AMP and glutathione was observed, neither substance was considered to be essential. The enzyme did not attack n-homoserine nor the lactones of L-homoserine or DL-homoserine. 

Two distinct serine dehydrases (deaminases), one active on the L and the other on the d form, have been prepared from E. and from... 

Binkley and Okeson purified the enzyme system that cleaves cystathionine and found that neither phosphate nor ATP was required for activity, thus correcting the previous report that ATP was required. In addition to splitting cystathionine, this enzyme preparation also produced H2S from cysteine. The authors suggest that their enzyme may be identical with cysteine desulfhydrase. Binkley also reported that he had been able to synthesize cystathionine enzymatically from homocysteine and serine by a fractionated liver preparation which had been freed from the cystathionine cleavage enzyme, serine dehydrase and homoserine deaminase. The activity of the enzyme synthesizing cystathionine was either inhibited or unaffected by ATP, DPN, AMP, and various metal ions. 

During this period I was frustrated by my inability to obtain tryptophan synthetase in pure form from Neurospora. Therefore, I searched for a more suitable enzyme for studies on protein structure alterations resulting from mutations. I characterized d- and L-serine deaminases from Neurospora - with this objective in mind but was unable to develop a convenient isolation procedure for mutants lacking these enzymes and so stopped these investigations. 

Serine is deaminated and dehydrated to pyruvate by serine deaminase (sometimes called serine dehydratase). 

Umbarger and Brown 233) have observed L- and D-threonine dehy-drases in E. coli which are stimulated by pyridoxal phosphate. In a continuation of this work 234) they have presented evidence that E. coli extracts contain two distinct L-threonine dehydrases. One of the dehydrases is the L-threonine dehydrase of Wood and Gunsalus and requires pyridoxal phosphate, AMP, and glutathione. It was found to be an adaptive enzyme, and was active against L-serine. The second dehydrase is present in extracts of wild-type E. coli, but not in mutants which are unable to convert threonine to a-ketobutyrate as a step in isoleucine synthe. It requires only pyridoxal-5-phosphate and is inhibited by isoleucine. On the basis of kinetic studies it is proposed that the Wood-Gunsalus dehydrase combines with one molecule of substrate, whereas the other enzyme combines with two. L-Serine is a substrate for both enz3unes. Evidence is presented for a third deaminase in E. coli cells which is serine-specific. 

More important evidence, however, is the widespread distribution and considerable activity of serine deaminase in different organisms. The anaerobic deamination of DL-serine by cell-free liver extracts has been ob-... 

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