584 NEW AND UNIDENTIFIED GROWTH FACTORS 



growth principle. It was designated vitamin Bt because of its ready water 

 solubility and its importance to the insect. 



Assays of vitamin Bp were carried out by placing 4-week-old T. molitor 

 larvae on a purified cassein-salts-glucose-cholesterol-vitamins diet, and 

 noting the growth response to sources of the vitamin over a 4- to 6-week 

 period. Using this assay, the vitamin was found in yeast, whey, and many 

 animal tissues. Vegetables, with the exception of wheat germ, were poor 

 sources. Isolation of the vitamin was effected from liver and whey^^' *^ 

 by adsorption on and elution from fullers' earth, extraction into phenol, 

 chromatography on alumina columns, and countercurrent extraction with 

 phenol-dilute HCl. The purified material was found upon characterization, 

 degradation, and synthesis studies to be identical with carnitine [(CH3)3- 

 N+— CH2CH(OH)CH2COO-], the trimethyl betaine of ^-hydroxy-7- 

 aminobutyric acid. 



The purified growth factor was active at levels of 0.37 to 0.75 7 per gram 

 of diet. This places the requirement at the catalyst level of activity, de- 

 spite the fact that in several animal tissues the carnitine content approaches 

 0.1% (it represents up to 3 % of the total water-soluble "extractives" of 

 skeletal muscle). The high activity for growth, in spite of the high content 

 in tissues, is reminiscent of choline. Moreover, the similarity in structure 

 to choline and the thetins suggests the possibility that carnitine may serve 

 as a methylating agent in vivo. Carter et al.,^^ acting on this supposition, 

 have tested crotonobetaine (a dehydration product of carnitine) and (3- 

 hydroxy-7-aminobutyric acid as possible replacements for carnitine in 

 Tenebrio. Only the latter compound was active, at levels of 12 to 24 7 per 

 gram of diet. The authors therefore suggested that carnitine may partici- 

 pate in transmethylation reactions in animal tissues. A similar postulate 

 was made earlier for carnitine in the human being^'^- ^^ on the basis of an 

 increased excretion of methylated pyridinium compounds (described as 

 trigonelline) after administration of carnitine. Thus, even though only a 

 few insect species closely related to Tenebrio (e.g., Palorus ratzeburgi^^) 

 appear to require an exogenous supply of carnitine, ^^ the interesting pos- 

 sibility that this compound may take a place among the group of import- 

 ant transmethylating agents in higher animals has been raised by this 

 work with lower forms. It is not unreasonable to hope that future researches 

 into the growth requirements of other phyla may bring to light additional 



65 G. Fraenkel, Arch. Biochem. and Biophys. 34, 468 (1951). 



58 H. E. Carter, P. K. Bhattacharyya, K. R. Weidman, and G. Fraenkel, Arch. Bio- 

 chem and Biophys. 38, 405 (1952). 

 " W. Ciusa and G. Nebbia, Bull. inst. polytech. Jassay 3, 181 (1948). 

 " W. Ciusa and G. Nebbia, Acta Vitaminol. 2, 49 (1948). 

 53 G. Fraenkel, Arch. Biochem. and Biophys. 34, 457 (1951). 



