Reaction coupling in ADH1A alcohol dehydrogenase enzyme by exciplex formation with adenosine diphosphate moderated by low-energy electronic excited states.

Abstract

Two commonly accepted theories about enzymes were revisited. The first states that adenosine triphosphate (ATP)-stored energy is only released when the substrate is in place, because the substrate changes the enzyme structure when it is bound to the enzyme. In fact, as demonstrated and discussed presently, no structural changes are required, and ATP-stored energy is released when it can be used. The second states that ATP-released energy moves along the enzyme molecule in the form of molecular vibrations (Davydov's vibrational solitons). In fact, as reported presently, energy released upon ATP hydrolysis moves in the form of excited-state electrons (excitons), with no molecular vibrations involved. The relevant experimental evidence was obtained for the human ADH1A alcohol dehydrogenase enzyme. Spontaneous ATP hydrolysis in the absence of substrate was apparently prevented by electronically excited enzyme + adenosine diphosphate (ADP) + inorganic phosphate (P) complex (exciplex) formed upon ATP hydrolysis. This exciplex kept ADP + P bound and in place for the inverse reaction, until the excess energy was dissipated in the enzyme-catalyzed reaction or by energy transfer to a suitable acceptor. Additionally, and contrary to textbooks, ADH1A has required ATP, working orders of magnitude faster in its presence.