Proline reductase and

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 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. 

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. 

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