Analogs of Pyridoxal or Pyridoxal Phosphate: Relation of Structure to Binding with Apoenzymes and to Catalytic Activity

Abstract

Publisher Summary This chapter focuses on analogs of pyridoxal or pyridoxal phosphate, and analyzes the relation of structure to binding with apoenzymes and to catalytic activity. Among the vitamins and coenzymes, pyridoxal (PL) and pyridoxal 5′-phosphate (PLP) are almost unique in that they slowly catalyze in dilute aqueous solutions at ambient temperatures or above, and at physiological pH values many of the same reactions of amino acids for which PLP-enzymes are required in vivo . Model studies with pyridoxal analogs permitted delineation of the structural features required for catalysis of such nonenzymatic reactions. In the pyridine series, these features are supplied by either 3-hydroxypyridine-2-aldehydeo or 3-hydroxypyridine-4-aldehyde—that is, substituents at the 2- and 5-positions of pyridoxal are not essential—whereas the formyl group at position 4, the phenolic group at position 3, and the heterocyclic nitrogen at position 1 are required. In this chapter, the effect of structure on enzymatic transamination of unphosphorylated compounds related to PL and PM is discussed. The effect of binding of PLP upon the conformation of PLP enzymes is explained. The activity of analogs of PLP in duplicating the effects of this coenzyme on conformation and activity of several PLP enzymes is also described.