Analysis of Biosynthesis Mechanism Associated with Molecular Structure of Natural Rubber

研究了天然橡胶分子结构与生物合成机理的关系。在超离心分离天然胶乳的底组分存在的情况下，用FDP和IDP对橡胶分子进行聚合。体外合成橡胶分子的结构表征表明，天然橡胶的起始物质与其他天然存在的顺式-1,4-聚异戊二烯不同。终止步骤被认为是天然橡胶所特有的。对天然胶乳进行粒度分馏，考察链伸长与粒径的关系。乳胶分别用14C-IDP、14C-IDP+FDP和140-IDP+GGDP孵育。橡胶链的伸长和终止与胶乳的粒径有关。采用核磁共振、GPO和粘度法对大、小粒径橡胶进行了表征。由小橡胶颗粒凝聚而成的橡胶是具有末端活磷酸基团的线状分子。相比之下，大橡胶颗粒中的橡胶是支链分子，末端是与脂肪酸相连的磷脂。研究了底分数存在下橡胶分子的体外合成机理，证明了IDP合成酶和碳源的存在。通过体外合成前后底组分的组成分析，确定了碳源。

Biosynthesis mechanism associated with molecular structure of natural rubber was investigated. The rubber molecule was polymerized by the addition of FDP and IDP in the presence of the bottom fraction isolated from natural rubber latex by ultra-centrifugation. The structural characterization of in-vitro synthesized rubber molecule showed that the initiating species of natural rubber was different from those of the other naturally occurring cis-1,4-polyisoprene. The termination step was presumed to be specific for natural rubber.The natural rubber latex was fractionated in particle size to investigate the relationship between chain elongation and particle size. The latex was incubated with 14C-IDP, 14C-IDP+FDP and 140-IDP+GGDP.The chain elongation and termination of the rubber was related to the particle size of the latex. The rubber in the small and large particle size was characterized by NMR, GPO and viscometry. The rubber coagulated from small rubber particle was linear molecule which has a living terminal phosphoric acid group. In contrast, the rubber from large rubber particle was branched molecule terminated with phospholipid linked to fatty acid.The mechanism of in-vitro synthesis for rubber molecule in the presence of bottom fraction was investigated to prove the presence of enzyme such as IDP synthase and carbon sources. The carbon source was identified by analyzing composition of bottom fraction before and after the in-vitro synthesis.