Leucine is the essential growth factor of a strain of amylase-producing bacteria, Bac. subtilis var. amyloliquefaciens FUKUMOTO K 49. However, some factor contained in the cell or yeast extract is additionally necessary for growth from spore of K 49. The factor was then explored in commercial powder of yeast extract. Active fraction was obtained by alcohol extraction followed with gel filtration through Sephadex G 15, 50 or 75 and presumed to be nucleoprotein by estimation of ninhydrin test and optical density. However, after phenol treatment of yeast extract according to the procedure preparing RNA, it was found that nucleic acid is not necessary for the growth. Then auxanography for growth factor of spore of K 49 was carried out with amino acids and disclosed that both isoleucine and valine are indispensable for the growth and one of them could not be omitted.
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