As reported in the previous paper¹⁾, mikamycin A inhibited the incorporation of ¹⁴C-amino acids into the hot acid-precipitable, trypsin-degestible fraction of the cells of Staphylococcus aureus and this inhibitory effect was demonstrated to be markedly enhanced by the addition of mikamycin B, despite that mikamycin B itself hardly affected ¹⁴C-amino acids incorporation.

A number of works have indicated that following three steps exist in the course of protein synthesis:

(1) Amino acid activation by specific enzymes in the presence of ATP^2,3,4)

(2) Transfer of activated amino acid to soluble ribonucleic acid^5,6)

(3) Protein formation from soluble RNA-amino acid complexes on the ribosome^6,7)

This paper presents some investigations in the various microorganisms on the site of action of mikamycins in the intermidiate steps of protien synthesis described above, especially on the point whether the site of inhibation by mikamycins is in the synthesis of protein itself or any preceding steps of amino acid transfer.