Combining Medium Effects and Cofactor Catalysis: Metal-Coordinated Synzymes Accelerate Phosphate Transfer by 108

The systematic exploration of the modification of polyethylene imine with guanidinium and octyl groups has led to the identification of a catalyst, CD6, which accelerates the phosphate transfer reaction of HPNP (2-hydroxypropyl-4-nitrophenyl phosphate) in the presence of divalent metals such as Zn2+, Co2+, Mg2+ or Ni2+. CD6 exhibits saturation kinetics that are described by Michaelis-Menten parameters K-m ranging from 2.5-8 mM and k(cat) ranging from 0.0014-0.09 s(-1). For Zn-II-CD6 this corresponds to an overall acceleration k(cat)/k(uncat) of 3.8 x 10(5) and a catalytic proficiency (k(cat)/K-m)/k(uncat) of 1.5 x 10(8). Catalysis by Zn-II-CD6 is specifically inhibited by inorganic phosphate, allowing turnover regulation by product inhibition. This effect stands in contrast to Zn-II-catalysed transesterification of HPNP in water or by the synzymes Co-II-CD6 and Ni-II-CD6, with which no such interference by product is observed. These characteristics render synzyme Zn-II-CD6 an efficient enzyme model that reflects enzyme-like properties in a wide range of features.