Enzymatic properties of human hageman factor fragment with plasma prekallikrein and synthetic substrates

Hageman factor fragment (HFf) was isolated from acetone-treated human plasma. The K m and k cat of HF f were determined with a natural substrate, plasma prekallikrein, and 34 synthetic amides and esters. The highest “catalytic efficiency”, k cat/K m, was found with prekallikrein (2,980 mM −1sec −1). Of the synthetic substrates D-Pro-Phe-Arg-pNA, Ac-Phe-Arg-OEt, Cbz-Arg-OMe, and Bz-Ile-Glu-Gly-Arg-pNA had the four largest k cat/K m values (130–670 mM −1s −1).