Fig. 5

Why does folate lower Hcy? In both panels, total folate is indicated on the x-axis with normal folate = 1. Panel a shows simulation results for the concentrations of Hcy (blue), remethylation flux from Hcy to Met (yellow), SAM (green), and betaine (red) in the normal male model as a function of total folate. Hcy decreases substantially as total folate increases. Panel b shows simulation results for the same quantities in the normal male if the allosteric effects (red arrows in Fig. 1) of SAM and betaine on CBS are removed. In this case, Hcy concentration is a constant independent of total folate. In both cases the flux from Hcy to Met increases as total folate increases. Thus, Hcy goes down as folate goes up because of the allosteric inhibition of CBS by SAM and Bet