Biosynthesis of chloramphenicol in Streptomyces species 3022a. Isotope incorporation experiments with [G-14C] chorismic, [G-14C] prephenic, and [G-14C, 6-3H] shikimic acids

Abstract

When chloramphenicol-producing cultures of Streptomyces species 3022a were administered [G-14C] chorismic, [G-14C] prephenic, and [G-14C, 6-3H] shikimic acids, radiochemical yields in the antibiotic were very low (0.01–0.1%). [G-14C] chorismic and prephenic acids labeled chloramphenicol to about the same specific activity as tyrosine, aspartic acid, and glutamic acid from mycelial protein, whereas protein phenylalanine was 100 times more active. We conclude that these two substrates are unable to penetrate the cell membrane and the radioactivity incorporated enters as [G-14C] phenylpyruvic acid. Labeled shikimic acid, on the other hand, was directly incorporated into the cells. The 14C: 3H ratio in chloramphenicol isolated after feeding the [G-14C, 6R-3H] and [G-14C, 6S-3H] labeled forms indicated that the pro-6R-hydrogen was eliminated during ring aromatization. Antibiotic labeled from [G-14C, 6S-3H] shikimic acid was chemically degraded to 2,4,6-tribromoaniline without change in the 14C: 3H ratio thus establishing the specific incorporation of shikimic acid into the phenyl ring, and locating the tritium at positions ortho to the propanoid substituent.