The Discovery of Avidin by Esmond E. Snell

A Constituent of Raw Egg White Capable of Inactivating Biotin in Vitro (Eakin, R. E., Snell, E. E., and Williams, R. J. (1940) J. Biol. Chem. 136, 801–802) The Concentration and Assay of Avidin, the Injury-producing Protein in Raw Egg White (Eakin, R. E., Snell, E. E., and Williams, R. J. (1941) J. Biol. Chem. 140, 535–543) Esmond Emerson Snell (1914–2003) was born in Salt Lake City, Utah. After receiving his Bachelor's degree in biochemistry from Brigham Young University in 1935, Snell was awarded a $400 scholarship to attend the University of Wisconsin in Madison. There he worked with W. H. Peterson, a biochemist interested in microbial metabolism. Snell's thesis project involved identifying growth factors for lactic acid bacteria by starting with a simple medium and determining what supplements were necessary for growth. Along with Frank Strong, Snell published an assay for riboflavin, which was the first widely used microbiological assay method for a vitamin and served as a prototype for assays for each of the B vitamins (1Snell E.E. Strong F.M. A microbiological assay for riboflavin.Ind. Eng. Chem. Anal. Ed. 1939; 11: 346-350Crossref Scopus (32) Google Scholar). (Incidentally, this paper was originally submitted to the Journal of Biological Chemistry (JBC), but it was rejected on the grounds that it was not biochemical enough and was more suited to a bacteriology journal.) Snell received his Ph.D. in 1938 and a year later joined Roger J. Williams at the University of Texas in Austin for a postdoctoral fellowship. His first project was to purify a new yeast growth factor that Williams and Robert E. Eakin discovered and named “biotic acid.” Because Koegl and Toennis (2Koegl F. Toennis B. Z. Physiol. Chem. 1936; 242: 43-73Crossref Scopus (55) Google Scholar) had identified biotin 3 years before, Williams requested a few micrograms of biotin from Koegl to differentiate between the two growth factors. Within a month, Snell found that biotin and biotic acid were one and the same. Nonetheless, Snell continued to study biotin, and this work is the subject of the two JBC Classics reprinted here. In the first paper of this set of JBC Classics, Snell reports on the finding that biotin can be inactivated in vitro by commercial egg albumin. Previous research had shown that chicks on a diet of raw egg whites were deficient in biotin despite an abundance of the vitamin in their diet, indicating that something in the egg whites was sequestering biotin (3Eakin R.E. McKinley W.A. Williams R.J. Egg-white injury in chicks and its relationship to a deficiency of vitamin H (biotin).Science. 1940; 92: 224Crossref PubMed Scopus (13) Google Scholar). To see if this interaction could be replicated in vitro, Snell added egg albumin to a sterile biotin solution and tested it for biotin activity using a yeast assay that he developed (4Snell E.E. Eakin R.E. Williams R.J. A quantitative test for biotin and observations regarding its occurrence and properties.J. Am. Chem. Soc. 1940; 62: 175-178Crossref Scopus (69) Google Scholar). Snell also purified the raw egg white component responsible for binding biotin and found that it could be dissociated from biotin by heating but not by dialysis or a change in pH. Later, Snell collaborated with Paul Gyorgy and confirmed that this egg white protein produced “egg white injury” when administered to rats (5Gyorgy P. Rose C.S. Eakin R.E. Snell E.E. Williams R.J. Egg-white injury as the result of nonabsorption or inactivation of biotin.Science. 1941; 93: 477-478Crossref PubMed Scopus (34) Google Scholar). In the second paper reprinted here, Snell describes a concentration procedure and an assay method for the egg white protein. By this time, the protein had been named “avidin” because of its affinity for biotin (avid + biotin). Snell determined that an acetone precipitation procedure with a salt extraction worked best for purification of avidin from egg whites. To develop this concentration procedure, Snell also had to come up with an avidin assay. The assay was a simple one in which avidin samples were added to two sterile aliquots of biotin, and one aliquot was heated to 100 °C for 15 min to denature the avidin. Snell then used his yeast assay for biotin to determine the difference in biotin content between the two aliquots and thereby establish how much avidin was present in the samples. Because biotin was so rare at the time, Snell never imagined that the vitamin would become a reagent for biotinylation of other biofactors and that avidin would be so widely used in purification. However, he did speculate on a future use for avidin when he stated in the first Classic, “The ability of this substance to take up and release biotin specifically and quantitatively suggests its possible use as a tool in the purification of biotin.” Snell went on to make many more important contributions to the field of nutritional biochemistry, including the discovery of the B vitamins folic acid and pantothenic acid, and the coenzyme forms of vitamin B6, pyridoxal, and pyridoxamine. Some of this work on the B vitamins will be the subject of a future JBC Classic. Snell's philosophy of science can be summarized by a message he once wrote for his students, “Hard work on interesting problems is enjoyable and preferable to aimless wasting of leisure time. It may also lead to unexpected findings that give insights into important related problems. Such unexpected findings—sometimes called “luck”—frequently happen to the active researcher, but only rarely to those who prefer talk to study and work. So one should study and work hard, on interesting problems of any nature, with the purpose of explaining nature and helping others.” 1Virtually all the biographical information for this Classic introduction was taken from Ref. 6Snell E.E. From bacterial nutrition to enzyme structure: a personal odyssey.Annu. Rev. Biochem. 1993; 62: 1-27Crossref PubMed Google Scholar and a paper by Miles and Metzler (E. W. Miles and D. E. Metzler (2004) Esmond Emerson Snell (1914–2003), submitted for publication). 1Virtually all the biographical information for this Classic introduction was taken from Ref. 6Snell E.E. From bacterial nutrition to enzyme structure: a personal odyssey.Annu. Rev. Biochem. 1993; 62: 1-27Crossref PubMed Google Scholar and a paper by Miles and Metzler (E. W. Miles and D. E. Metzler (2004) Esmond Emerson Snell (1914–2003), submitted for publication).