Molecular and Biochemical Basis for Stable Carbon Isotope Ratios in Marine Autotrophs Using Form IC and ID RubisCO

稳定碳同位素数据在生态学和地球科学中有着广泛的应用。 这些同位素分馏的数据影响了我们对发生在分子到全球尺度上的过程的理解。 过去的气候，模型约束的命运，今天的温室气体排放量，营养转移的推论在复杂的生态系统中，酶和细胞控制初级生产力的阐明都使用了稳定的碳同位素分馏数据（d13 C值）。 RubisCO是卡尔文循环中的CO2固定酶，是地球上最重要的催化碳固定的酶，被光合自养生物和化能自养生物广泛使用。 目前，在自养生物中已经描述了RubisCO的五种形式：形式IA-D和形式II，它们在结构和催化性质上不同。 至少有4种形式对海洋的初级生产力有重要贡献。 到目前为止，RubisCO的动力学同位素效应（KIE），即固定的C的d13 C与所用的CO2底物不同的程度，仅确定了一种IA型RubisCO（蛤Solemya的化能自养共生体; 24.5.），两种IB型酶（菠菜和聚球藻PCC 6301; 29和22.，分别）和两种形式II的（Rhododocellum rubrum和Riftia pachyptila共生体; ~18.两者）。 确定不同RubisCO的KIE对于理解、解释和模拟海洋学和全球碳中的d13 C值至关重要。 PI正在评估IC型和ID RubisCO的KIE，以估计这些酶的同位素分馏的全范围。 RubisCO酶正在从代表性的海洋浮游植物和自养细菌中分离和纯化。 他们正在从模式物种中研究IC RubisCO 球形红细菌和海洋分离物S185- 9A 1，并形成ID RubisCO来自球石藻Emiliania huxleyi和硅藻中肋骨条藻。 分离的蛋白质在氨基酸序列、组成、Vmax和Km（CO2）方面进行表征。 最后，动力学同位素效应正在通过高精度方法确定。

Stable carbon isotope data are used widely in ecology and earth sciences. These data on isotope fractionations influence our understandings of processes occurring on molecular to global scales. Hindcasts of past climates, models constraining the fates of present day greenhouse gas emissions, inferences of trophic transfers within complex ecosystems, and elucidation of enzyme and cellular controls on primary productivity have all used stable carbon isotope fractionation data (d13C values). RubisCO, the CO2-fixing enzyme for the Calvin Cycle, is by far the most important enzyme catalyzing carbon-fixation on earth, used widely by photoautotrophs and chemoautotrophs. Presently, five forms of RubisCO have been described in autotrophs: Forms IA-D, and Form II, which differ in their structure and catalytic properties. At least 4 forms contribute significantly to primary productivity in the ocean. To date, the kinetic isotope effects (KIEs) for RubisCOs, the degree to which the d13C of the C fixed differs from the CO2 substrate used, have only been determined for one form IA RubisCO (chemoautotrophic symbionts of the clam Solemya; 24.5.), two form IB enzymes (spinach and Synechococcus PCC 6301; 29 and 22., respectively) and two form II's (Rhodospirillum rubrum and Riftia pachyptila symbionts; ~18. for both). Determining the KIEs of different RubisCOs is critical to understanding, interpreting, and modeling of d13C values in oceanography and global carbon. The PIs are assessing the KIEs for form IC and ID RubisCOs, to estimate the full range of isotope fractionations by these enzymes. The RubisCO enzymes are being isolated and purified from representative marine phytoplankton and autotrophic bacteria. They are studying form IC RubisCO from the model species Rhodobacter sphaeroides and marine isolate S185-9A1, and form ID RubisCO from the coccolithophore Emiliania huxleyi and the diatom Skeletonema costatum. The isolated proteins are being characterized with respect to amino acid sequence, composition, Vmax, and Km (CO2). Finally, the kinetic isotope effects are being determined by high precision methods.