Makamycin is a member of a group of antibiotics including streptogramin^1,17), PA 114^2,18) staphylomycin^3,19), and ostreogricin (E 129)^4,20), and was isolated from a cultured material of Streptomyces mitakaensis in our laboratory⁵⁾. Later two mikamycins, mikamycins A and B, were extracted and purified, and their strong synergistic relation was reported ⁶⁾. Structures of these two mikamycins were studied and they were confirmed to be quite different each other. Mikamycin B is a cyclic peptide, having lactone linkage and being constituted of 3-hydroxypicolinic acid, L-threonine, L-4-oxopipecolic acid, D-α-aminobutylic acid, L-phenylglycine, L-proline, and L-p-dimethylamino-N-methyl-phenylalanine^7,8). The formula of A, C₃₁H₃₉O₉N₃, and hydrolysis studies by Okabe⁹⁾ indicated its quite different structure from B. These different structures of A and B suggested their different action mechanisms. It is an interesting problem, whether A and B showing such a strong synergism would inhibit different steps in a same series of metabolism, or they would depress those in different series of metabolism .

In this paper, studies on effects of mikamycins A and B on synthesis of protein and nucleic acids are presented.