抄録
Investigations were made on the reaction between pyridoxal and DL-homocysteine and the physical and chemical properties of the reaction product, pyridoxal-DL-homocysteine (I). The ultraviolet spectra of (I) have been studied at various pHs in buffer solution and in dioxane-water. In neutral aqueous solution, it has two absorption maxima, one at 332 mμ and the other at 251 mμ and the dipolar ionic form predominates but significant amounts of the uncharged forms are also present. Dissociation constants obtained by spectrophotometric method are pK_1=2.2,pK_2=7.2,pK_3=9.4 and the value of equilibrium Kz between dipolar ionic and uncharged neutral forms is about 5. For the separation of (I) from the reaction product, paper electrophoresis is most suitable. The reaction of pyridoxal and homocysteine is seemed to proceed by two steps and the velocity constants for hemiacetal formation and the formation of the cyclic product under various pHs and concentrations of reactants has been studied. An aqueous solution of (I) is comparatively unstable at 50℃ but is stabilized in an excess of homocysteine, particularly at PH 9.0.
