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Chapter 68 : Looking Back
This chapter talks about the biotin and its importance. It was interesting, in an age of PCR, DNA sequencing, and diffusion gradient chambers, to find authors building on work done with relatively primitive techniques. Our understanding of biotin had been completely transformed over the intervening decades. The new understanding ranges far and wide, from the function of biotin as the prosthetic group of several carboxylases to its deficiency as the cause of inherited disorders in babies and possibly of antibiotic-associated diarrhea, too. Biotin deficiency was virtually unknown, because the vitamin is ubiquitous in foods, because it is synthesized by bacteria in the intestine, and because it is required in vanishingly tiny quantities anyway. Researchers simply wanted to know how the biochemistry and ultrastructure of S. cerevisiae changed when deprived the organism of biotin. The first infant diagnosed with a metabolic disorder had an extensive skin rash and chronic neurological abnormalities but improved dramatically when given biotin orally. Most investigators used a microbiological assay to estimate the concentrations of biotin in plasma and other fluids. The two organisms most favored for this purpose were Lactobacillus plantarum and Ochromonas danica, whose growth provides an extremely sensitive measure of the level of the vitamin. Biotin may therefore be used as a covalent label for (macro) molecules, which can be detected with labeled avidin or streptavidin. First exploited in immunochemical tissue staining, this remarkable affinity is now used to enhance signal detection in immunoassays and DNA probe diagnostics.