Phosphopyridoxal cyclic compounds with histamine and histidine. 7: The properties of pyridoxal and phosphopyridoxal cyclic compounds with histamine and histidine.

Cyclic compounds synthesized from histamine (Hi) or histidine (His) with pyridoxal (PL)--[Hi-PL, His-PL] and Hi or His with pyridoxal 5'-phosphate (PLP)--[Hi-PLP, His-PLP] were tested for stability in buffer, acid and base solutions, crude homogenates of various tissues and in the presence of enzymes which metabolize Hi or His. The cyclic pyridoxal compounds were stable in all experimental conditions, whereas phosphopyridoxal cyclic products were degraded by rat intestinal DAO and rat intestine homogenate, apparently enzymatically. In acidic and basic solutions changes in migration velocity and u.v. absorption spectrum occur. The characteristic fluorescence of these cyclic compounds is described.