Valine coordinately increases the levels of three of the enzymes participating in the biosynthesis of isoleucine and valine in Mycobacterium pellegrino. The amount of valine required for end-product induction depends on the condition of the cells. Isoleucine inhibits the effect of valine. Acetohydroxy acid synthetase, the enzyme catalyzing the first common step in the biosynthesis of valine and isoleucine, is inhibited by valine. The induction effect of valine appears to be due to its ability to inhibit the activity of this enzyme, thus causing isoleucine deficiency, which in turn leads to derepression. This conclusion is supported by the fact that valine, under certain conditions, inhibits growth.

Fromthe culture broth of Streptomyces griseoflavus a new orange red basic antibiotic named cytotetrin complex was isolated by solvent extraction. The complex was fractionated into five active components, cytotetrins A, B, C, D and E, respectively. The physical, chemical and biological properties of each cytotetrin are discussed. They are active against Gram-positive microorganisms and some tumors. Cytotetrin is related to nogalamycin. In the course of screening for new antitumor antibiotics, it has been found that a neworange red basic antibiotic complexis produced by a streptomycete isolated from a soil sample. The organism designated as S-191 proved to be identical with Streptomyces griseoflavus "CBS-Cifferi" (Bucsav 7, 13). The antibiotic complex produced by S. griseoflavus No. S-191 is especially active against Gram-positive bacteria and moreover exhibits some antitumor activity. The components of the antibiotic complex were separated, obtained in crystalline state and identified as new antibiotics of the anthracycline family. These antibiotics were named cytotetrin complex and its single components designated as cytotetrins A, B,,