In many microorganisms, the putative orthologs of the
            Escherichia coli
            ygbB
            gene are tightly
 linked or fused to putative orthologs of
            ygbP
            ,
 which has been shown earlier to be involved in terpenoid biosynthesis.
 The
            ygbB
            gene of
            E. coli
            was expressed in
 a recombinant
            E. coli
            strain and was shown to direct the
 synthesis of a soluble, 17-kDa polypeptide. The recombinant protein was
 found to convert 4-diphosphocytidyl-2C-methyl-
            d
            -erythritol
 2-phosphate into 2C-methyl-
            d
            -erythritol
 2,4-cyclodiphosphate and CMP. The structure of the reaction product was
 established by NMR spectroscopy using
            13
            C-labeled substrate
 samples. The enzyme-catalyzed reaction requires Mn
            2+
            or
 Mg
            2+
            but no other cofactors. Radioactivity from
 [2-
            14
            C]2C-methyl-
            d
            -erythritol
 2,4-cyclodiphosphate was diverted efficiently to carotenoids by
 isolated chromoplasts from
            Capsicum annuum
            and, thus,
 was established as an intermediate in the deoxyxylulose phosphate
 pathway of isoprenoid biosynthesis. YgbB protein also was found to
 convert 4-diphosphocytidyl-2C-methyl-
            d
            -erythritol into
 2C-methyl-
            d
            -erythritol 3,4-cyclophosphate. This compound
 does not serve as substrate for the formation of carotenoids by
 isolated chromoplasts and is assumed to be an
            in vitro
            product without metabolic relevance.
          
在许多微
生物中,Escherichia coli的ygbB
基因的推定同源物通常与ygbP的推定同源物紧密链接或融合在一起,而ygbP早已被证明参与
萜类化合物的
生物合成。大肠杆菌的ygbB
基因在
重组的大肠杆菌菌株中表达,并被证明可以指导合成一种可溶性的17 kDa
多肽。发现
重组蛋白质可以将4-二
磷酸胞苷基-2C-甲基-d-赤藓糖醇2-
磷酸转化为2C-甲基-d-赤藓糖醇2,4-环二
磷酸和
CMP。使用13C标记的底物样品,通过NMR光谱法确定了反应产物的结构。酶催化的反应需要Mn2+或Mg2+,但不需要其他辅因子。[2-14C]2C-甲基-d-赤藓糖醇2,4-环二
磷酸的放射性能有效地被
辣椒素细胞色素体转化为类
胡萝卜素,并因此被确定为异
戊烯类化合物
生物合成的去氧
木糖磷酸途径的中间体。发现YgbB蛋白还可以将4-二
磷酸胞苷基-2C-甲基-d-赤藓糖醇转化为2C-甲基-d-赤藓糖醇3,4-环
磷酸。这种化合物不能作为细胞色素体形成类
胡萝卜素的底物,被认为是一种无代谢相关的体外产物。