28 微生物による植物ステロール側鎖切断反応のメカニズムについて

概要

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The mechanism of microbial degradation of the branched hydrocarbon side chain of phytosterol, e.g. sitosterol (2) and campesterol (3) was investigated employing Mycobacterium sp. NRRL B3805. From the experimental results using intact cells, the intermediacy of 26-hydroxysitostenone (7), 3-oxostigmast-4-en-26-oic acid (8) and 3-oxo-4-cholenic acid (5) was established. Cell free studies gave us the following conclusive results. Exposure of [28-^<14>C]-8 to the cell free extracts resulted in the formation of radioactive propionic acid with all of the radioactivity residing in carbon 2 of the molecule. When unlabelled 8 was again incubated in the presence of [^<14>C]-NaHCO_3, 5% of the radioactivity was found in propionic acid with all of the radiolabel residing in carbon 1. When this cell free system was incubated with 3-oxoergost-4-en-26-oic acid (16) and [^<14>c] -NaHCO_3, radioactive acetic acid was formed. Degradation of the molecule revealed that carbon 1 contained most of the radioactivity. Hence, cleavage of the phytosterol side chains by this microorganism involves the incorporation of CO_2 onto the C-28 position of the phytosterol molecules, followed by carbon-carbon bond fission at C-24, 25 and C-24, 28 as shown in scheme 2.
天然有機化合物討論会の論文
1982-09-10