The origin of sulfur in biotin.

The comparative ability of Escherichia coli K-12 hpb lambda-, a biotin overproducing strain, to incorporate 35S from isotopically labeled L-methionine, L-cystine, and the sulfane sulfur of thiocystine was determined. Comparison of the specific activity of sulfur in biotin produced by the organism with that of the 35S-labeled amino acids demonstrates that the sulfur of cystine is transferred to biotin with an efficiency of at least 75%, that the sulfur of methionine does not contribute to biotin significantly, and that the sulfane sulfur of thiocystine contributes approximately one-third of the sulfur to newly synthesized biotin and is essentially equivalent in utilization to that of the other two sulfur atoms in the molecule.