Investigations were continued on the nature of the growth factor requirements of gravis, strain Dundee. Hypoxanthine, or adenine + guanine, or adenine + xanthine, were found capable of replacing concentrates of the growth factor from liver and yeast.

Nucleoside and nucleotide fractions, prepared from electrophoretically-purified ribonucleic acid, were unable to replace the free purine bases. A purine extract was obtained from an active fish-liver concentrate by copper precipitation. In this extract, a large amount of hypoxanthine and a smaller amount of xanthine were found by chromatography to be the major purine constituents; traces of adenine and guanine were also detected. Chromatographic fractionation and spectro-photometric examination of the fractions confirmed the presence of hypoxanthine and xanthine, whose concentrations were estimated.

The purine extract supported less growth than the original fish-liver concentrates. Growth on the purine extract could be reproduced by a mixture of hypoxanthine and xanthine at an equivalent concentration.


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