Huppe H C, Buchanan B B
Division of Molecular Plant Biology, University of California, Berkeley 94720, USA.
Z Naturforsch C J Biosci. 1989 May-Jun;44(5-6):487-94. doi: 10.1515/znc-1989-5-624.
A chloroplast type of fructose-1,6-bisphosphatase, a central regulatory enzyme of photosynthetic carbon metabolism, has been partially purified from Chlamydomonas reinhardtii. Unlike its counterpart from spinach chloroplasts, the algal FBPase showed a strict requirement for a dithiol reductant irrespective of Mg2+ concentration. The enzymes from the two sources resembled each other immunologically, in subunit molecular mass and response to pH. In the presence of dithiothreitol, the pH optimum for both the algal and spinach enzymes shifted from 8.5 to a more physiologic value of 8.0 as the Mg2+ concentration was increased from 1 to 16 mM. At 1 mM Mg2+, a concentration estimated to be close to physiological, the Chlamydomonas FBPase was active only in the presence of reduced thioredoxin and was most active with Chlamydomonas thioredoxin f. Under these conditions, the enzyme showed a pH optimum of 8.0. The data suggest that the Chlamydomonas enzyme resembles its spinach counterpart in most respects, but it has a stricter requirement for reduction and less strict reductant specificity. A comparison of the properties of the FBPases from Chlamydomonas and spinach will be helpful for elucidating the mechanism of the reductive activation of this enzyme.
一种光合碳代谢的核心调节酶——叶绿体类型的果糖-1,6-二磷酸酶，已从莱茵衣藻中部分纯化出来。与菠菜叶绿体中的对应酶不同，藻类果糖-1,6-二磷酸酶（FBPase）无论Mg2+浓度如何，都对二硫醇还原剂有严格要求。这两种来源的酶在免疫学、亚基分子量和对pH的响应方面彼此相似。在二硫苏糖醇存在的情况下，随着Mg2+浓度从1 mM增加到16 mM，藻类和菠菜酶的最适pH值都从8.5转变为更接近生理值的8.0。在1 mM Mg2+（估计接近生理浓度）时，莱茵衣藻FBPase仅在存在还原型硫氧还蛋白时才具有活性，并且对莱茵衣藻硫氧还蛋白f的活性最高。在这些条件下，该酶的最适pH值为8.0。数据表明，莱茵衣藻的这种酶在大多数方面与其菠菜对应酶相似，但它对还原作用的要求更严格，而对还原剂特异性的要求则不那么严格。比较莱茵衣藻和菠菜的FBPases特性将有助于阐明该酶还原激活的机制。
