There is only a slight difference between the corresponding Michaelis constants (Kmocoo-, = 2,7. 10-3-m.; Km(Dcoo-) =3,1.10-3-m.). Consequently there is an almost linear relationship between the rates of reaction and the ratio (HCOO-/DCOO-).N o isotopic effect can be observed in the reoxidation of the reduced DPN.