The Course of Thiamin Metabolism in Man as Indicated by the Use of Radioactive Sulfur.

When supplementary thiamin (Vitamin B,) is ingested or injected, the amount which appears in the urine during the succeeding twenty-four hours usually increases, but the total additional excretion always falls short of the supplement, even when the vitamin is injected and there can be no question of incomplete absorption. We have sought information on this unaccounted-for moiety by synthesizing thiamin from sulfur which contains the radioactive isotope S35 (designated as B,*) and by following, after injection of the B,*, the excretion of the radiosulfur (S*) in the urine and feces and the excretion of total free B, in the urine. Radiosulfur was prepared by bombarding elementary sulfur with 7.5 MEV. deuterons, and thiamin bromide hydrobromide containing S36 was synthesized from the bombarded sulfur.' The half-life of radiosulfur is about 88 days and it emits negative electrons with a maximum energy of o.io7 MEV.2 This long half-life makes extended observations possible; some samples showed measurable activity 18 months after the radiosulfur had been prepared. The radioactive vitamin was injected intramuscularly in two series of experiments; in the first series the subject, a young man in good health, was on a vitamin Br-free diet for 36 days prior to the first injections and for the 15 days of the experimental period; in the second series the same subject was on a normal diet. Essentially the same results were obtained in both series. Free (unphosphorylated) vitamin B, was determined in the urine by a modification of the thiochrome method. The urinary sulfur compounds were fractionated into the inorganic sulfate, ethereal sulfate and neutral sulfur components, the sulfur of each component was converted into elementary sulfur,3 and the radioactivity of the sulfur was then measured quantitatively by comparison with a standard sample of the same radio-sulfur. In the feces only the total radiosulfur was determined. The radioactivity measurements were made with open, coincidence Geiger counters. The sulfide-coated copper counter tubes and the samples were enclosed in a large partially evacuated bell jar, provided with an externally operated arrangement for moving the samples successively to a definite position in front of the counters. The standard Rossi coincidence 412 PROC. N. A. S.