Pyridoxal phosphate catalysis

The versatile chemistry of pyridoxal phosphate offers a rich learning experience for the student of mechanistic chemistry. William Jencks, in his classic text. Catalysis in Chemistry and Enzymology, writes ... 

Dunathan, H. C. Stereochemical aspects of pyridoxal phosphate catalysis. Advan. Enzymol. 35, 79-134 (1971). 

The addition of cofactors to antibodies is a sure means to confer a catalytic activity to them insofar as this cofactor is responsible for the activity. Indeed for many enzymes, the interaction with cofactors such as thiamins, flavins, pyridoxal phosphate, and ions or metal complexes is absolutely essential for the catalysis. It is thus a question there of building a new biocatalyst with two partners the cofactor responsible for the catalytic activity, and the antibody which binds not only the cofactor but also the substrate that it positions in a specific way one with respect to the other, and can possibly take part in the catalysis thanks to some of its amino acids. 

Lactobacillus delbrueckii. In 1953, Rodwell suggested that the histidine decarboxylase of Lactobacillus 30a was not dependent upon pyridoxal phosphate (11). Rodwell based his suggestion upon the fact that the organism lost its ability to decarboxylate ornithine but retained high histidine decarboxylase activity when grown in media deficient in pyridoxine. It was not until 1965 that E. E. Snell and coworkers (12) isolated the enzyme and showed that it was, indeed, free of pyridoxal phosphate. Further advances in characterization of the enzyme were made by Riley and Snell (13) and Recsei and Snell (14) who demonstrated the existence of a pyruvoyl residue and the participation of the pyruvoyl residue in histidine catalysis by forming a Schiff base intermediate in a manner similar to pyridoxal phosphate dependent enzymes. Recent studies by Hackert et al. (15) established the subunit structure of the enzyme which is similar to the subunit structure of a pyruvoyl decarboxylase of a Micrococcus species (16). 

Mortland, M. M. (1984). Deamination ofglutamic acid by pyridoxal phosphate-Cu2+-smectite catalysts. Journal of Molecular Catalysis, 27, 143-55. 

Nucleophilic catalysis is a specific example of covalent catalysis the substrate is transiently modified by formation of a covalent bond with the catalyst to give a reactive intermediate. There are also many examples of electrophilic catalysis by covalent modification. It will be seen later that in the reactions of pyridoxal phosphate, Schiff base formation, and thiamine pyrophosphate, electrons are stabilized by delocalization. 

Effective concentration 65-72 entropy and 68-72 in general-acid-base catalysis 66 in nucleophilic catalysis 66 Elastase 26-30, 40 acylenzyme 27, 40 binding energies of subsites 356, 357 binding site 26-30 kinetic constants for peptide hydrolysis 357 specificity 27 Electrophiles 276 Electrophilic catalysis 61 metal ions 74-77 pyridoxal phosphate 79-82 Schiff bases 77-82 thiamine pyrophosphate 82-84 Electrostatic catalysis 61, 73, 74,498 Electrostatic effects on enzyme-substrate association rates 159-161... 

Enzyme catalysis can be employed to detect concentrations of metabolites such as blood sugar, urea, uric acid or ATP. The metabolite is often best reacted with a co-enzyme such as NADPH or pyridoxal phosphate which changes its UV-vis absorption spectrum upon reaction. 

The stereochemistry of pyridoxal phosphate-catalyzed reactions was last summarized comprehensively in 1971 by Dunathan [2], who outlined many of the basic concepts in this field. Aspects of PLP catalysis have been discussed in other reviews on enzyme reaction stereochemistry (e.g., [9]), and a brief review, emphasizing their own work, has recently been published by the present authors [ 10]. Much work has been done in this field during the past ten years, most of it supporting the concepts laid out in Dunathan s review, often refining the picture and sometimes modifying the original ideas. 

Unlike other pyridoxal phosphate-dependent enzymes, in which it is the carbonyl group that is essential for catalysis, the internal Schiff base between pyridoxal phosphate and lysine in glycogen phosphorylase can be reduced with sodium borohydride without affecting catalytic activity. Thus, while pyridoxal phosphate is essential for phosphorylase activity, it does not act by the same kind of mechanism as in amino acid metabolism. 

Metzler DE, Ikawa M, SneU EE (1954) Metal ion catalysis in oxidative transaminations by pyridoxal phosphate. J. Amer... 

M21. Musajo, L., Benassi, C. A., Longo, E., and Allegri, G., Preliminary report on the presence in human urine of substances influencing pyridoxal phosphate-dependent enzymes. Proc. Symp. Chem. Biol. Aspects Pyridoxal Catalysis, Rome, 1962 pp. 333-341 (1963). Pergamon Press, New York. 

CO factors, such as NAD, bind only momentarity to the enzyme others, such as vitamin remain bound to the enzyme before, after, and during the event of catalysis. In the caste of vitamin B -iequiring enzymes, the cofactor occurs in the forms pyridoxal phosphate and pyridoxamine phosphate. 

The same scaffold was used to design catalysts for pyridoxal phosphate-dependent deamination of aspartic acid to form oxaloacetate, one half of the transamination reaction [8], and oxaloacetate decarboxylation [14]. Catalysis was due to binding of pyridoxal phosphate in close proximity to His residues capable of rate limiting 1,3 proton transfer. A two-residue catalytic site containing one Arg and one Lys residue was found to be the most efficient decarboxylation agent, more efficient per residue than the Benner catalyst, most likely due to a combination of efficient imine formation, pK depression and transition state stabilization. 

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