Enzyme pyridoxal phosphate, coenzyme tabl

Chemical Properties of Thiamin. 2. Catalytic Mechanisms 743. .. Table 14-3 Some Enzymes That Require Pyridoxal Phosphate as a Coenzyme... 

Table 6.1 lists the water-soluble vitamins with their structures and coenzyme forms. Certain portions of the coenzymes are especially important in their biological activities, and they are indicated by arrows. For example, in case of coenzyme A, a thiol ester is formed between its -SH residue and the acyl group being transferred. And in the case of pyridoxal phosphate, its carbonyl residue forms a Schiff base with the amino group of the amino acid that is being decarboxylated. Fat-soluble vitamins (Table 6.2) are also transformed into biologically active substances. However, with the possible exception of vitamin K, these do not operate as prosthetic groups or cosubstrates in specific enzyme reactions. 

The carboxylases have for their coenzyme pyridoxal phosphate which acts according to the mechanism described on p. 174. A whole series of decarboxylases exists, each being specific for the L-form of a given amino add. Certain of them have been isolated from animal tissues such as liver and kidney, but the majority have been isolated from micro-organisms in which the enzymes appear if their specific substrate is present in the culture medium. In micro-organisms therefore these decarboxylases are adaptive enzymes. The amines produced by the decarboxylation of amino acids (Table XIII) often possess pharmacological activity this is the case for histamine, the product of the decarboxylation of histidine. 

---