Figure 3. Structural similarity to pyruvate renders malonate and oxaloacetate allosteric inhibitors of L-lactate dehydrogenase.

(a) Alignment of the X-ray crystallographic structures generated for rabbit muscle L-LDH co-crystallized with oxaloacetate (red) and NADH (cyan); or with malonate (gold). Active site of L-LDH with (b) oxaloacetate (OAA), or with (c) malonate. (d) These inhibitors are structural analogues of pyruvate and are found to bind all to the same non-competitive site. (e) Oxaloacetate is a non-competitive inhibitor of L-LDH with respect to pyruvate. Enzyme kinetics were determined spectrophotometrically (n=3) and fit according to a non-competitive model (R²=0.93). Error bars=mean±s.d.