STUDIES ON THE DISTRIBUTION OF VITAMIN BT (CARNITINE)

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  • GFG. Fraenkel
    G. Fraenkel
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Abstract
1. The procedure in the bio-assay of BT (carnitine) with the use of Tenebrio molitor as the subject has been described. The minimum requirements of carnitine to give optimal survival and nearly optimal growth of the Tenebrio larva are 0.35 µg. per gram of the dry diet. For optimal growth 1.5 µg. per gram are required. 2. Yeast and Neurospora contain about 35 µg. carnitine/g., and wheat 7-14 µg./g. No evidence of the presence of carnitine could be obtained from Escherichia coli, Tetrahymena geleii and corn. 3. Synthesis of carnitine takes place in two insect species (Dermestes and Phormia) which do not require it in the diet, while Tenebrio, which requires it in the diet, shows no sign of synthesis under any conditions. The growing Tenebrio larva retains more than 50% of the carnitine which it takes up in the diet. 4. Little carnitine was found in the hen's egg. It is synthesized in sizeable quantities in the growing chick embryo. 5. In mammalian tissues, by far the largest quantities of carnitine, about 1000 µg./g. of dry tissue, occur in the skeletal muscle. Corresponding figures for other tissues were: heart 560, bladder 280-560, kidney 412, liver 140-280, small intestine 224, brain 87, nerve 70-140 and blood 35 µg./g. dry tissue. 6. In dog muscle which had been paralyzed for several weeks, the carnitine content was not significantly changed. Liver after autolysis had the same carnitine content as before. 7. The carnitine content of pooled samples of human urine was 28-56 µg./ml. In different individuals levels as low as 14-28 and as high as 132-264 µg./ml. were found. This variation depended on the carnitine content of the diet, with the highest figures after a heavy meat meal or a three-day period of starvation, and the lowest after a vegetable diet. Blood contains fairly uniform levels of 7-14 µg./ml. 8. Different commercial preparations of meat extracts had carnitine contents of one to three per cent (dry weight). 9. Since carnitine occurs universally, or almost universally in biological material, and an organism either synthesizes it, or else requires it as a "vitamin," it is considered to be of vital importance in the metabolism of most or all forms of life.

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