Dissociation Constants of Ternary Complexes of Fatty Acids and Fatty Acid Amides with Horse Liver Alcohol Dehydrogenase-Coenzyme Complexes.

Abstract

Fatty acids form dissociable binary compounds with liver alcohol dehydrogenase (ADH), and ternary compounds with DPN-ADH, but not with DPNH-ADH. The fatty acids compete with alcohols for the same binding site. The amides of fatty acids form binary compounds with ADH, and ternary complexes with DPN-HADH, but not with DPN-ADH. They compete with aldehyde for the same binding site. Spectrophotofluorometric methods were elaborated for determining all the dissociation constants involved KEJ; KEO; KEOI; and KEIO in the case of fatty acicids, KEP KER; KERI; and KEIR the case of amides. With increasing C-chain length the complex forming power increases for both acids and amides, in some of the combinations many thousand-fold. For the fatty acids this increase continues up to C15. From C16 and upwards the complexing ability practically disappears. In these ternary complexes coenzyme and substrate analog mutually stabilize one another''s binding to the enzyme. The high affinity of the long-chain fatty acids and amides for ADH-DPN or ADH-DPNH is paralleled by the high reaction velocities observed with higher alcohols and aldehydes in comparison with ethanol. The significance of these results is discussed.