Selenocysteine lyase

Selenocysteine lyase Increased for Se (decreased if chloroplast expression) Increased for Se ... 

PLP-dependent enzymes catalyze the following types of reactions (1) loss of the ce-hydrogen as a proton, resulting in racemization (example alanine racemase), cyclization (example aminocyclopropane carboxylate synthase), or j8-elimation/replacement (example serine dehydratase) (2) loss of the a-carboxylate as carbon dioxide (example glutamate decarboxylase) (3) removal/replacement of a group by aldol cleavage (example threonine aldolase and (4) action via ketimine intermediates (example selenocysteine lyase). 

Aspartate y-decarboxylase Selenocysteine lyase NifS protein of nitrogenase Gamma elimination and replacement Cystathionine y-synthase Cystathionine y-lyase Threonine synthase... 

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-... 

Deagen, J.T., Butler, J.A., Beilstein, M.A., and Whanger, P.D. 1987. Effects of dietary selenite, selenocysteine and selenomethionine on selenocysteine lyase and glutathione peroxidase activities in rat tissues. J. Nutr. 117, 91—98. 

Thus, the y-phosphate group of ATP is transferred to some group of the protein and the enzyme phosphoryl intermediate is attacked by the selenide generating the only known direct phosphorus-selenium bond in biology. The ADP, which stays complexed to the enzyme is concomitantly hydrolyzed to AMP, and thus thermodynamically drives the overall reaction. Sulfide does not serve as a substrate even at high concentrations, so SPS is one of the few enzymes that can discriminate between its Se substrate and the sulfur homolog. Recent evidence also indicates that the actual substrate is not free selenide but rather some selenium species generated from selenocysteine via the activity of one of the selenocysteine lyases present in the cell. ... 

Daher R, Van Lente F. 1992. Characterization of selenocysteine lyase in human tissues and its relationship to tissue selenium concentrations. J Trace Elem Electrolytes Health and Dis 6 189-194. 

Selenocysteine lyase (SCL) from higher eukaryotes is the mammalian counterpart to bacterial enzymes and is thought to play a vital role in the metabolism of selenium in the cell. " SCL has been shown to be similar in amino acid composition to the NifS family, thus suggesting a similar mechanism used to generate elemental... 

Fig. 6.3 Generalized overview of Se metabolism in plants. Numbers denote known enzymes. (1) ATP sulfurylase, (2) adenosine-5-phosphosulfate reductase, (3) glutathione or sulfite reductase, (4) glutathione reductase or O-acetylserine thiol lyase, (5) Selenocysteine methyltransferase, (6) Selenocysteine lyase, (7) cystathionine-g-synthase, (8) cystathionine-b-lyase, (9) methionine synthase, (10) methionine methyltransferase, (11) DMSP lyase, (12) g-gjutamylcysteine synthetase (Source Parker et al. (2003), Sors et al. (2005b), Pilon-Smits and Quinn (2010), Lindblom et al. (2012), Yu and Gu (2013), PUon-Smits et al. (2014), Winkel et al. (2015) and PUon-Smits (2015))...

Degradation of selenocysteine is catalyzed by selenocysteine lyase, which releases elemental Se, and this is then reduced to selenide by glutathione or other thiols. The urinary excretion pathway is very important for selenium homeostasis of the tissues. Urinary selenium tends to reflect recent intake rather than tissue status, but it can be a useful source of information about possible selenium overload. 

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