Irreversible inhibition of 3-hydroxy-3-methylglutaryl-coenzyme A synthase from yeast by F-244 and (RS)-β-butyrolactone

The inhibition of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) synthase from yeast was compared for both F-244 (1) and (RS)-β-butyrolactone (5). F-244 exhibits irreversible inhibition with an IC₅₀ of 8 nM, similar to that reported for the rat liver enzyme, while the binding constant (1/K(I)) and inactivation rate constant (k(inact)) are similar to values reported for the human cytoplasmic enzyme. (RS)-β-Butyrolactone (5) also irreversibly inhibits the enzyme, but with much lower efficieny (IC₅₀ 2 mM). The values for K(I) (9 mM) and k(inact) (0.0078 s^-1) for 5 were determined. The results show that k(inact) for 5 and 1 differ by a factor of only 2.5, while K(I) for 5 is higher by a factor of 1.8 x 10⁵. Hence, the β-lactone ring is shown to be the sole essential structural feature in 1 for irreversible inactivation of HMG-CoA synthase; however, the remaining functionality enhances the binding of 1 to the enzyme relative to 5.