II. CHEMISTRY 553 



F. COMPLEX BIOTIN COMPOUNDS 



In natural i)r()(liu'ts biotin occurs mainly in bound fonn (p. 529). The 

 biological activity of various tissue extracts in animals and in microor- 

 ganisms, including yeast cells, shows variations, depending on the form in 

 which biotin was isolated from these sources. Complete hydrolysis will 

 lead to free l)iotin. One of the simple biotin compounds, the chemical struc- 

 ture of which is now well established, is biocytin.^*"^' 



1. BlOCYTIN 



The term biocytin (from the Greek kutos, meaning cell) has been used 

 to designate the biotin compound occurring in many soluble natural prod- 

 ucts, especially during the controlled autolysis of actively metabolizing 

 yeast .^'^' ^^ Biocytin is characterized by its differential availability as source 

 of biotin in microbiological assays using various test organisms. Biocytin 

 may be utilized as biotin by Lactobacillus casei, Lactobacillus delbruckii 

 LD J, Lactobacillus acidophilus, Streptococcus fecalis R., Neurospora crassa, 

 and Saccharomyces carlsbergensis. In contrast Lactobacillus arabinosus, Lac- 

 tobacillus pcntosus, and Leuconostoc mesenteroides P-60 will respond only 

 to free biotin. Strong acid hydrolysis (at least 3 A^ at 120° for 1 hour) will 

 liberate biotin or its microbiological equivalent from biocytin. No enzymes 

 have been found as 3^et which will cleave the complex and release biotin.^"- ^^ 

 In no biological system thus far studied has biocytin shown more activity 

 than can be accounted for on the basis of its biotin content. During the 

 isolation of biocytin drastic conditions such as extremes of pH, heat, or 

 oxidizing conditions were avoided in order to prevent the formation of 

 artifacts or even of derivatives. Countercurrent distribution in different 

 S3^stems showed only one biotin-containing peak. Finally, crystalline bio- 

 cytin has a microbiological spectrum or activity identical with that of the 

 biotin complex of yeast extract as shown by bioautographic paper strip 

 chromatography. Thus it appears that biocytin, as isolated from yeast 

 extract, is identical with the compound as it occurs in its natural form. 



The isolation of crystalline biocytin from yeast extract involved the 

 following steps :^^ adsorption on Norit; elution with aqueous ammonia; 

 adsorption on Super Filtrol-Celite; elution with aqueous ethanolic am- 

 monia; chromatography on Super Filtrol-Celite; chromatography on alu- 



" I.. D. Wright uiul II. R. Skeggs, Proc. Soc. Ezptl. Biol. Med. 56, 95 (1944). 



Si* L. D. Wright, ?]. L. Cres.son, H. R. Skeggs, T. R. Wood, R. L. Peck, D. E. Wolf, 



and K. Folkers, /. Am. Chem. Soc. 72, 1048 (1950). 

 »» L. D. Wright, E. L. Cresson, H. R. Skeggs, R. L. Peck, D. E. Wolf, T. R. Wood, 



J. Valiant, and K. Folkers, Science 114, 635 (1951). 

 *' L. D. Wright, E. L. Cresson, H. R. Skeggs, T. R. Wood, R. L. Pock, D. E. Wolf, 



and K. Folkers, ./. Ain. Chem. Soc. 74, 1996 (1952). 



