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Synthesis of Thiamine in the Digestive Tract of the Rat^1,2,

Lobund, Department of Biology, University of Notre Dame, Notre Dame, Indiana

S³⁵O₄⁼ was administered by stomach tube and cecal injection to adult rats to study the availability of flora-synthesized thiamine. The flora of the digestive tract was found to incorporate radiosulfate into the in situ formed thiamine molecule, possibly via the cysteine or methionine routes.

The main site of microbial synthesis was in the cecum, although the possibility of synthesis in the small intestine could not be entirely excluded. Little or no absorption of the flora-synthesized radiothiamine occurred as shown by the lack of radiothiamine in hearts and livers. The contribution of the intestinal flora towards the thiamine requirement of the host thus seems at best low and relatively unimportant. Since most radiosulfate is absorbed as such from the intestinal tract, the negative findings in hearts and livers also exclude tissue synthesis of a pattern found in intestinal bacteria.

Upon centrifugation of a homogenate of cecal contents at 1600 rpm, the cecal supernatant contained two to three times more thiamine than the residue, although the specific activity of the thiamine of each was approximately the same. The thiamine in the cecum appeared to be tied to a large (possibly apo-coenzyme) complex. This, indeed, might account for lack of utilization of flora-synthesized thiamine by the host animal.

² A preliminary report of some of this work was presented before the 5th International Nutrition Congress, 1960, Washington, D.C.

³ St. Mary's College, Notre Dame, Indiana.

Manuscript received 14 January 1961.