Abstract
Thiaminase II catalysis was analysed according to our rate-equations of the second-order enzymatic reaction. (1) Thiaminase II attacks pseudo-basic thiamine as well as that of quarternary ammonium type. (2) Thiaminase II catalysis proceeds through the cyclic steady state such as thiaminase II→ thiaminase II-OH^-→ thiamine-thiaminase II-OH^-→ thiamine-thiaminase II→ thiaminase II. The ternary complex, thiamine-thiaminase II-OH^- yields the products. (3) The enzyme-substrate complex of ammonium-type thiamine is more dissociable than that of pseudo-basic thiamine and is attacked in relatively higher substrate concentration. (4) The rate of the enzymatic reaction is remarkably affected by ionic strength of the medium. Addition of salt within 3×10^<-2>M makes the rate faster than original by promoting the formation of substrate-enzyme complex of ammonium-type thiamine. More addition of salt results in a decrease of the rate following to the Debye-Huckel's relation.
