Reductases proline reductase

D-proline reductase Anaerobic respiration Clostridium sticklandii 104, 105... 

Once identified as a selenoprotein in this model (C. sticklandii), the need for selenium was also shown for C. sporogenes The addition of selenium to the culture medium was reported to improve the level of D-proline reductase activity as early as 1976, ° yet the first identification of the selenoprotein component of this enzyme did not occur until more recentiy in 1999 by Andreesen s group. It is quite clear now from data from these model systems, as well as from DNA sequence analysis of the grd aiiAprd operons, ° ° that Stickland reactions are common to many amino acid-fermenting clostridia. Those that are capable of proline reduction all... 

Table 12.1 summarizes the selenoenzymes isolated from Clostridia, which fall into three major categories. The first group is the amino acid reductases, such as GR, sarcosine reductase (SR), betaine reductase (BR), and proline reductase (PR). The second class of selenoenzymes includes FDH. Although a number of clostridial species are suspected to contain a... 

Clostridium sticklandii also expresses a proline reductase that can reduc-tively cleave proline to 8-aminovalerate (Seto and Stadtman 1976). PR was first purified by Seto and Stadtman (1976) by following the decomposition of proUne in the presence of dithiothreitol or NADH. They found PR to have a denatured mass of approximately 30kDa (sodium dodecyl sulfate-polyacrylomide gel electrophoresis SDS-PAGE) and a native size of approximately 300 kDa. The addition of selenite to the growth medium of C sticklandii did increase the specific activity of PR in extracts by threefold however, no selenium was detected in the purified enzyme. It should be noted that this purified enzyme had lost the ability to couple reduction of proline to NADH and thus probably was missing one or more components of the complete enzyme complex. 

Kabisch UC, Grantzdorffer A, Schierhom A, et al. 1999. Identification of D-proline reductase from as a selenoenzyme and indications for a catalytically active pyruvoyl group derived from a cysteine residue by cleavage of a proprotein. J Biol Chem 274 8445-54. 

Seto B. 1980. Chemical characterization of an alkali-labile bond in the polypeptide of proline reductase from Clostridium sticklandii. J Biol Chem 255 5004-6. 

Stadtman TC, Elliott P. 1957. Studies on the Enzymatic Reduction of amino acids II. Purification and properties of ao-proline reductase and a prohne racemase from Clostridium sticklandii. 1 Biol Chem 228 983-97. 

This pyruvate-dependent enzyme [EC 1.4.4.1], also referred to as D-proline reductase (dithiol), catalyzes the reaction of 5-aminopentanoate with hpoate to produce D-proline and dihydrolipoate. Other dithiols can function as reducing agents. 

NITRATE REDUCTASE NITRITE REDUCTASE PHENOL HYDROXYLASE PROLINE DEHYDROGENASE PUTRESCINE OXIDASE PYRUVATE OXIDASE SALICYLATE 1-MONOOXYGENASE SUCCINATE DEHYDROGENASE SULFITE REDUCTASE XANTHINE OXIDASE Falling ball viscometry,... 

PROLINE REDUCTASE D-Proline reductase, borohydride reduction, BOROHYDRIDE REDUCTION D-Proline reductase (dithiol),... 

PROLINE REDUCTASE L-Proline to D-proline interconversion, PROLINE RACEMASE PROLIPOPROTEIN SIGNAL PEPTIDASE PROLYL 3-HYDROXYLASE PROLYL 4-HYDROXYLASE PROLYL ISOMERASE... 

Other pyruvate-containing enzymes include aspartate -decarboxylase from Escherichia coli, the enzyme that catalyzes the formation of -alanine for the synthesis of pantothenic acid (Section 12.2.4) proline reductase from Clostridium sticklandiv, phosphatidylserine decarboxylase from E. coli and phenylalanine aminotransferase from Pseudomonas fluorescens. Phospho-pantetheinoyl cysteine decarboxylase, involved in the synthesis of coenzyme A (Section 12.2.1), and S-adenosylmethionine decarboxylase seem to be the only mammalian pyruvoyl enzymes (Snell, 1990). 

This enzyme consists of three different proteins. A, B, and C, in which a polypeptide with MW 12,000 (also known as selenoprotein A) contains selenium as selenocysteine in a unique site and the protein B with an MW of 200,000 possesses an essential carbonyl group, probably pyruvate . The system has several characteristics similar to proline reductase and may function by a related mechanism. It remains unclear, however, why selenium would be required for such a mechanism, nor is it obvious how the ATP is produced. 

Proline racemase occurs in Clostridium sticklandii, which produces 8-aminovalerate from L-proline. Proline racemase and D-proline reductase are responsible for the conversion L-proline is racemized by proline racemase to form D-proline, which is converted into 5-aminovalerate by D-proline reductase (E.C. 1.4.4.1). 

Pyruvoyl cofactor is derived from the posttranslational modification of an internal amino acid residue, and it does not equilibrate with exogenous pyruvate. Enzymes that possess this cofactor play an important role in the metabolism of biologically important amines from bacterial and eukaryotic sources. These enzymes include aspartate decarboxylase, arginine decarboxylase," phosphatidylserine decarboxylase, . S-adenosylmethionine decarboxylase, histidine decarboxylase, glycine reductase, and proline reductase. ... 

Two enzymes that contain the pyruvoyl cofactor are not decarboxylases D-proline reductase and glycine reductase. These enzymes were originally reported to contain the pyruvate in an ester linkage, but later studies have demonstrated its presence at the N-terminus of one of the subunits linked by the peptide amide bond. In contrast to the pynivoyl-dependent decarboxylases, the site of internal cleavage and modification of these reductases is a cysteine rather than a serine. The mechanism of post-translational biosynthesis of the pyruvoyl cofactor in these enzymes could conceivably proceed through the same mechanism shown in Scheme 1 but with the cysteine sulfur performing the role of the serine oxygen. 

Under slightly different conditions, using 1,3-propanedithiol, acyloins and acyloin acetates lead to the formation of 1,3-dithianes where hydrogen has replaced the hydroxyl or acetoxyl groups . Hydrolysis to the ketone provides a method of converting acyloins to ketones and desulphurization allows conversion of acyloins to hydrocarbons (equation 10). Reduction of l,l-dimethyl-5-hydroxysila-4-cycloheptanone gave l,l-dimethylsila-4-cycloheptanone by this method (equation 11) . A similar reaction is believed to be involved in the action of D-proline reductase . ... 

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