Pyruvoyl enzymes

A number of enzymes that catalyze the same reactions as do pyridoxal phosphate-dependent enzymes contain a catalytic pyruvate residue at the amino terminal of the peptide chain. The catalytic mechanism is assumed to be the same as for pyridoxal phosphate-dependent enzymes, except that the proton donor is a glutamate residue rather than lysine. 

The most smdied enzyme is histidine decarboxylase from Lactobacillus 30a. There are pyruvate residues at the amino terminals of each of 5 of the 10 subunits in this enzyme. When the organism is grown on [ C] serine, the specific radioactivity of the pymvate is the same as that of serine incorporated into the protein and much greater than that of free lactate or pyruvate in the culture medium This suggests that pyruvate arises by postsynthetic modification of a serine residue. 

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). 

PQQ is present tis a noncovedently hound coenzyme in bacterial enzymes, and organisms that are incapable of its de novo synthesis can import it from the culture medium. It is synthesized by reaction between glutamate and tyrosine residues in a small (24 amino acid) peptide that is coded for by one of the bacterieil genes known to be required for PQQ synthesis (Stites et al., 2000b). 

No mammalian enzymes have been shown to utilize PQQ or TTQ as a cofactor, although there is some evidence PPQ may be a dietary essential. Mice fed a defined diet completely devoid of PQQ show impaired growth, friable skin with hemorrhages, hunched posture, decreeised fertility, emd fewer mitochondria, which 2ue less viable in vitro than normal. These abnormedities eu e corrected by providing 1 nmol (300 ng) of PQQ per g diet (Stites et al., 2000a). It is not known how much PQQ may normally be present in foods, nor how much may be synthesized by intestinal bacteria. 

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Structures of Thiamin-Dependent Enzymes 4. The Variety of Enzymatic Reactions Involving Thiamin 5. Oxidative Decarboxylation and 2-Acetylthiamin Diphosphate. 6. Thiamin Coenzymes in Nerve Action 753. .. Table 14-4 Some Pyruvoyl Enzymes... 

Figure 14-11 Schematic diagram of the active site of the pyruvoyl enzyme histidine decarboxylase showing key polar interactions between the pyruvoyl group and groups of the inhibitor O-methylhistidine and surrounding enzyme groups. Aspartate 63 appears to form an ion pair with the imidazolium group of the substrate.268 Hydrogen bonds are indicated by dotted lines. See Gallagher et al.269...

The mechanism of splicing is related to the chemistry of pyruvoyl enzyme activation (Eq. 14-41), succinimide formation from asparagine residues (Eq. 2-24), and protein carboxymethylation (Box 12-A). The intein always contains serine or cysteine in its N-terminal (l)-position and asparagine in its C-terminal position. The latter is always followed by cysteine, serine, or threonine in the N-terminal... 

Enzymes Containing Bound Biotin Enzymes Dependent upon Thiamin Diphosphate as a Coenzyme Some Enzymes That Require Pyridoxal Phosphate as a Coenzyme Some Pyruvoyl Enzymes... 

The mechanism of splicing is related to the chemistry of pyruvoyl enzyme activation (Eq. 14-41), succinimide formation from asparagine residues (Eq. 2-24), and protein carboxymethylation (Box... 

Kim AD, Graham DE, Seeholzer SH, Markheun GD (2000). S-Adenosylmethionine decaiboxylase from the archaeon Methanococcus jannaschii identification of a novel family of pyruvoyl enzymes. J Bacteriol 182 6667-6672... 

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