[Studies on the thiamine transport system in Bacillus cereus (author's transl)].

The thiamine transport system in Bacillus cereus exhibits rhythmical changes of resorption- and excretion-phases lasting 1-2 h. These main phases are subdivided in shorter ones with an average duration of 45 s. The velocity of the thiamine uptake is influenced by pH, temperature, age of cells, energy and substrate supply and thiamine concentration of the medium. The Michaelis-Menten-Kinetic can be used to describe the uptake: Km = 1.98 x 10(-8) M; Vmax = 1.19 x 10(-6) mol/g dry weight x min. The rate is enhanced by K+, Ca2+ and Mg2+, and inhibited by Pyrithiamin, EDTA, H+-ions, proton donors and proton acceptors; OH(-)-ions cause a change in the direction of transport. A theoretical explanation can be given by assuming a coupling of the thiamine permeation with proton movements in the membrane.