METABOLISM 



References to Section lo 



I. V. P. Sydenstricker, S. A. Singal, A. P. Briggs, N. M. de Vaughn and 

 H. Isbell, Science, 1942, 95, 176 ; /. Amer. Med. Assoc, 1942, 

 118, 1 199. 

 2. A. Brown, Glasgow Med. J., 1948, 29, 309. 



II. 2VIETABOLISM OF BIOTIN 



Sydenstricker et al.'^ found the amount of biotin excreted in the 

 urine by human subjects on a normal diet to be 29 to 52 /xg. per day, 

 which fell to 3-5 to 7-3 ^g. per day after seven to eight weeks on a 

 biotin-deficient diet. After administration of 75 to 300 /xg. of biotin 

 per day the urinary excretion increased after three to five days to 

 55 /^g- P^J^ <i^y- T. W. Oppel ^ reported an excretion of i^ to iii /xg. 

 per day by normal subjects on an imrestricted diet, and Gardner et al.^ 

 an excretion of 11 to 183 /xg. per day. The amount increased as 

 much as five-fold immediately following the administration of a 

 large dose of crude biotin by mouth. The faecal excretion varied from 

 17 to 208 /xg. per day and also increased when biotin was given by 

 mouth. 



The precise nature of the excretion product of biotin has not been 

 determined, but it is known that some at least of the biotin in normal 

 rat and human urine does not combine with avidin.2» * D. Burk and 

 R. J. Winzler ^ gave specific names to the different fractions, e.g., the 

 heat-labile, avidin-uncombinable fraction active for yeast but not 

 Rhizobium was termed miotin, the heat-stable, avidin-combinable 

 component was termed tiotin, and the avidin-combinable fraction 

 inactive for yeast but active for Rhizobium was termed rhiotin. 

 Miotin and tiotin were transformed into an avidin-combinable form 

 by yeast, but they were not identical with the diamino carboxylic 

 acid (page 407), as they were not converted into biotin by the action 

 of phosgene. 



The amount of biotin in human milk was small for the first four 

 or five days after parturition, and then rose gradually to 0-38 /xg. per 

 100 ml. by the tenth day. The amount in the mature milk was o-8o 

 to 0-82 /xg. per 100 ml.^ 



References to Section 11 



1. V. P. Sydenstricker, S. A. Singal, A. P. Briggs, N. M. de Vaughn 



and H. Isbell, Science, 1942, 95, 176 ; /. Amer. Med. Assoc, 

 1942, 118, 1199. 



2. T. W. Oppel, Amer. J. Med. Sci., 1942, 204, 886. 



3. J. Gardner, H. T. Parsons and W. H. Peterson, Arch. Biochem., 



i945» 8, 339 ; Amer. J. Med. Sci., 1946, 211, 198. 



28 433 



