P-20 好熱性古細菌Sulfolobusに特徴的なカルジトールの生合成と古細菌特有の糖代謝との関連 : 環化に関わる基質特異性の著しく緩い酵素の存在の可能性(ポスター発表の部)
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The lipid of thermophilic archaea is characteristic ether-bonded isoprenoidal macrocyclic lipid and consist of a double-face monolayer membrane. Furthermore, the genus Sulfolobus, has a characteristic lipid named carditoglycerolcaldoarchaeol (GDCT). GDCT has a 5-membered carbocycle bonded with glycerol by ether linkage. Gambacorta et al and our group performed the biosynthetic studies of calditol and the occurrence of cyclization of glucose to the 5-membered carbocycle was proved, However, the key step of cyclization, the involvement of catalytic oxidoreduction, was not shown by these results directly, while the inversion of C-4 stereochemistry at glucose to calditol was needed to occur. Furthermore, some of the enzymes of the central metabolism of Sulfolobus have shown to posses a "substrate promiscuity" that enables to catalyze glucose and galactose with a similar degree. So, the observation of the fate of hydrogen of glucose and galactose at C-4 within the calditol formation in Sulfolobus acidcaldarius were performed. At first, glucose and galactose labeled at C-4 were synthesized. Then, GDCT was isolated from hydrolysate of extracted lipid and converted to its acetate and ^1H NMR was observed. The C-4 hydrogen at the carbocycle of calditol was highly deuterated. The deuterium incorporation from glucose was 35%. Interestingly, the deuterium-incorporation experiment of galactose at C-4, the deuterium incorporation was 22 and 27%. The results indicate galactose was converted to the carbocycle of calditol with a similar extent, and suggest the substrate promiscuity was also expressed to the cyclization enzyme of calditol. Further the lower incorporation of deuterium at the C-4 of glucose compared with the incorporation of glucose labeled at the C-1 and C-6 suggest the involvement of a single enzyme of cyclization and the oxidoreduction on the C-4 at the cyclization reaction. Unique glycerol conversion to calditol carbocycle was also observed by chirally-labeled glycerol-incorporation experiments.
- 2005-09-15
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