448 VITAMIN Bi2 



animals, being greatest below the ileocecal valve. ^^ It is suggested that in 

 man the normal requirement of vitamin B12 is met by bacterial synthesis 

 in the colon. ^"^ 



Various tissues have been examined for vitamin B12. Beef samples have 

 been found to contain twice as much vitamin B12 as normal pork samples.*^ 

 Of the various organs investigated, the kidney has been found to contain 

 the greatest amount of vitamin B12.*" 



VII. Estimation 



THOMAS H. JUKES and WILLIAM L. WILLIAMS 



A. PHYSICAL 



The ultraviolet and visible absorption spectra of the cobalamins may 

 be used in measuring their concentration in solutions which are free from 

 interfering substances. Values for the extinction coefficients of vitamins B12 

 and Bi2b have been reported in the literature. Vitamin B12 has a sharp peak 

 at 361 mn,^ E\'^cm. = 204, and a broader peak in the \dsible region at 550 

 m/i,- -fi'Hin. — 63. These maxima and values are not appreciably altered 

 by changes in the pH of the solution. Vitamin Bi^b has similar maxima at 

 351 m/i, i5J{'^V. = 167, and 525 m/i, ^}1'm. = 57.=^ The values apply only 

 to acid or neutral solutions, for in alkaline solution these maxima of vita- 

 min Br2b undergo a bathochromic shift.'* Other E]"^^^ vsdues for absorption 

 maxima have been reported as follows: for ^'itamin B12 at 362 m^t, 194; 

 at 552 m/Lt, 59; for vitamin Bi2b at 351 mn, 165; at 527 mju, 56.^ 



The name vitamin Bi2a was proposed for a compound with specific physi- 

 cal and biological properties which was prepared by catalytic hydrogena- 

 tion of vitamin B12 followed by oxidation with atmospheric oxygen.^ The 



I" W. J. C. Dyke, H. G. Hind, D. Riding, and G. E. Shaw, Lancet 258, 486 (1950). 

 " U. D. Register, U. J. Lewis, H. T. Thompson, and C. A. Elvehjem, Proc. Soc. 



Exptl. Biol. Med. 70, 167 (1940). 

 12 U. J. Lewis, U. D. Register, and C. A. Elvehjem, Proc. Soc. Exptl. Biol. Med. 71, 



508 (1949). 



1 B. Ellis, V. Petrow, and G. F. Snook, J. Pharm. Pharmacol. 1, 60 (1949). 



2 N. G. Brink, D. E. Wolf, E. A. Kaczka, E. L. Rickes, F. R. Koniuszy, T. R. Wood, 

 and K. Folkers, J. Am. Chem. Soc. 71, 1854 (1949). 



3 J. V. Pierce, A. C. Page, Jr., E. L. R. Stokstad, and T. H. Jukes, J. Am. Chem. 

 Soc. 72, 2615 (1950). 



* J. A. Brockman, Jr., J. V. Pierce, E. L. R. Stokstad, H. P. Broquist, and T. H. 



Jukes, J. Am. Chem. Soc. 72, 1942 (1950). 

 6 W. G. Jackson, G. B. Whitfield, W. H. DeVries, H. A. Nelson, and J. S. Evans, 



J. Am. Chem. Soc. 73, 337 (1951). 

 « E. A. Kaczka, D. E. Wolf, and K. Folkers, /. Am. Chem. Soc. 71, 1514 (1949). 



