title: An alternative presentation of metabolism: Enzyme-catalyzed reactions can be viewed as atoms flowing through sluice gates.
abstract: Why should we think of enzymes as sluice gates? We are used to talk about "metabolic flux": I should like to suggest that we should indeed envision metabolism as a "liquid" flowing in different channel segments, each of which contains a single metabolite. Enzymes facilitate chemical reactions without affecting the reaction equilibrium, creating, or destroying matter: they can be visualized as "sluice gates" (mobile metal or wooden plates that control water flow in channels and sluices: Fig. 1), or, rather, as openings in metal or wooden plates that block the channel. Metabolism control and homeostasis maintenance are equivalent to controlling the water flux while maintaining the water level in each channel segment approximately constant. The "gates" representing non cooperative (Michaelis-Menten) and cooperative enzymes have very different shapes, reflecting their different roles in metabolic regulation: the activity of noncooperative enzymes catalyzing irreversible reactions has the greater effect over the flux, but cooperative enzymes are necessary to maintain homeostasis when irreversible reactions are involved.
authors: From the Université Libre de Bruxelles, Laboratoire de Chimie Biologique et de la Nutrition, Faculté de médecine, CP611, 808 Route de Lennik, 1070 Brussels, Belgium. mawaelbr@ulb.ac.be.
authors: Magali
authors: M
authors: Waelbroeck