Relationship between thiamin phosphorylation and intestinal transport in vitro: effect of chloroethylthiamin.
The effect of Chloroethylthiamin (CET), a structural analog of thiamin, on thiamin pyrophosphokinase (TPKase) activity of the supernatant of rat isolated enterocytes was compared with that on thiamin intestinal transport by rat everted jejunal sacs. Thiamin- thiazol-2(14C) was used as a substrate both for TPKase activity and for thiamin serosal transport and uptake. CET strongly inhibited TPKase activity of isolated enterocytes: at molar concentrations 10 or 100 times higher than labeled thiamin, the inhibition was 57 and 100% respectively. The inhibition was of the competitive type, with a Ki = 15 microM. At a molar concentration 10 times higher than labeled thiamin, CET lowered the thiamin serosal transport by 60%, and the sac wall content of free and phosphorylated thiamin by 54 and 42% respectively. At the 1:10 thiamin: CET molar ratio, the extent of the reductions of TPKase activity (57%) and of phosphorylated thiamin content of intestinal sac walls (42%) were of the same order. This indicates a relationship between the two events. Moreover, since TPKase activity inhibition alone resulted in the lowering of labeled thiamin serosal transport, thiamin phosphorylation and transport are probably two strictly related processes.
D000818:Animals; D001692:Biological Transport; D007408:Intestinal Absorption; D007422:Intestines / Q000201:enzymology; D010766:Phosphorylation; D051381:Rats; D013836:Thiamin Pyrophosphokinase / Q000032:analysis; D013831:Thiamine / Q000031:analogs & derivatives* / Q000378:metabolism* / Q000494:pharmacology
C004527:beclotiamine; D013836:Thiamin Pyrophosphokinase; D013831:Thiamine