. The actinomycetes. Actinomycetales. BIOGENESIS OF ANTIBIOTICS 73 Table 26 Neutralization by DL-threonine of DL-isoIeucine inhibition of aciinotnycin production (Kawamata et al. , 1960) Actinomycin production Incubation Control DL-Isoleucine lOO/ig. ml DL-Isoleucine 100yu?'ml + DL-threonine 100 ng/m\ days 2 0 0 0 4 100 0 200 6 400 0 400 7 2000 0 800 8 4000 0 1000 9 4000 0 4000 of proline into certain actinomycin peptides. The results obtained support the view that sarcosine competes with and replaces pro- line in the peptide of certain actinomycins (Katz and Goss, UJoS). Kawamata et al. (1960
. The actinomycetes. Actinomycetales. BIOGENESIS OF ANTIBIOTICS 73 Table 26 Neutralization by DL-threonine of DL-isoIeucine inhibition of aciinotnycin production (Kawamata et al. , 1960) Actinomycin production Incubation Control DL-Isoleucine lOO/ig. ml DL-Isoleucine 100yu?'ml + DL-threonine 100 ng/m\ days 2 0 0 0 4 100 0 200 6 400 0 400 7 2000 0 800 8 4000 0 1000 9 4000 0 4000 of proline into certain actinomycin peptides. The results obtained support the view that sarcosine competes with and replaces pro- line in the peptide of certain actinomycins (Katz and Goss, UJoS). Kawamata et al. (1960) found that addi- tion of DL-isoleucine to the medium (starch- glutamate-salts) represses the formation of actinomycin, whereas growth of the organ- ism is not adversely affected and is exen stimulated. The addition of 1 mg per ml of isoleucine l)rought about complete inhibition of antibiotic production. The addition of DL-threonine to the mediiun completely reversed this repressive effect, as shown in Table 26. Antibiotics Dcrirahh from Acetate ERYTHUOMYCIX Erythromycin has two sugar-like groups attached to a large lactone nucleus. The lactone nucleus is made up of seven pro- pionic acid units (Woodward, 11)")7). Acetic, propionic, and valeric acids may be incor- porated into the lactone ring. This is true especially of propionic acid, a fact which suggests that this acid is an important pre- cursor, and that the other two acids are converted into it before incorporation. Gerzon et al. (1956) suggested that the macrolide ring arises, at least in the erythro- mycins, by a process analogous to that by which many long-chain molecules are built from acetate, but utilizing propionate in- stead. The long carbon chains of such anti- biotics as the methymycins, picromycin, and narbomycin would be deri\'ed in essentially the same way except for incorporation of one acetate moiety. Alusilek and Sevcik (1958a) demonstrated that the addition of sodium arsenite (final concentration o
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