Homoserine dehydrase

Mammalian tissues contain enzymes that catalyze the nonoxidative deamination of serine, threonine, and homoserine. Since the postulated reaction mechanism involves a dehydration before the deamination, these enzymes are called dehydrases. L-Serine, L-threonine, and L-homoserine dehydrases have been partially purified and all are specific for the L-amino acid. Serine and threonine dehydrases require pyridoxal phosphate, ATP, and glutathione for activity. Pyridoxal phosphate requires the homoserine enzyme, but the need for ATP and glutathione has not been demonstrated. The reaction is likely to involve the formation of a Schiff base. The homoserine dehydrase has been... 

Serine, Threonine, and Homoserine Dehydrases. This group of enzymes catalyzes a nonoxidative deamination reaction resulting from a primary dehydration of the substrate. Serine, threonine, and homoserine have been shown to be deaminated by bacteria " " and animal tissues (liver) 101. 

Serine, Threonine, and Homoserine Dehydrases. This group of enzymes catalyzes a nonoxidative deamination reaction resulting from a primary... 

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. 

Both isomers of both serine and threonine are deaminated by Neuro-spora extracts 225-228). The enzymes involved have been purified by Yanofsky and his associates 225-228). A specific D-serine and D-threonine dehydrase has been purified thirty-five- to fortyfold from this mold 2f ). An absolute requirement for pyridoxal phosphate was demonstrated. No requirement for AMP or glutathione could be demonstrated. Some indication of a metal requirement was observed. The preparation was not active with the li-isomers of serine and threonine or DL-homoserine and DL-homo-cysteine. The rate of deamination of D-threonine is very slow compared to that with L-serine. Activity was observed with D-glutamic acid and D-as-partic acid. Since other D-amino acids were not deaminated by the preparation, these results could not be due to a contamination with D-amino acid oxidase. Furthermore, when either of these amino acids was incubated in the presence of D-serine, the keto acid production was a summation of that for each substrate alone. Pyridoxal phosphate had no effect on keto acid formation from the dicarboxylic amino acids. It is of interest that D-amino acid oxidase of Neurospora does not attack D-serine or D-threonine (77). 

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See also in sourсe #XX -- [ ]

See also in sourсe #XX -- [ , ]

See also in sourсe #XX -- [ , , , , ]

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