福建闽南地区汉族与畲族的指长比

本文旨在研究福建闽南地区汉族和畲族指长比(R)的特点。随机选择福建闽南地区汉族506例（男性173例,女性333例）,畲族450例（男性231例,女性219例）,采用体质测量法,测量并计算左右侧6项指长比（R_2/3、R_2/4、R_2/5、R_3/4、R_3/5、R_4/5）。福建闽南地区汉族和畲族左、右侧指长比均呈R_2/3<R_2/4<R_3/4<R_2/5<R_4/5<R_3/5的趋势;汉族女性指长比左侧R_2/3、R_2/4、R_2/5、R_3/4、R_3/5和右侧R_2/3、R_2/4、R_2/5高于汉族男性（P<0.05）;畲族女性指长比左侧的R_2/3、R_2/4、R_2/5和右侧R_2/3、R_2/4高于畲族男性（P<0.05）;畲族男性指长比左、右侧R_2/3、R_2/4、R_2/5、R_3/5、R_4/5高于汉族男性（P<0.05）;畲族女性指长比左侧R_2/3、R_2/4和右侧R_2/3、R_2/4、R_2/5、R_4/5高于汉族女性（P<0.05）。同民族不同性别两侧R_2/4百分比分布差异有统计学意义,不同民族同性别右侧R_2/4百分比分布差异有统计学意义。福建闽南地区汉族和畲族指长比存在性别、侧别的不同,与其他地区、族群也存在差异。     

荒漠草原猪毛蒿种群繁殖特征的土壤驱动因子分析

繁殖是植物生命活动的重要环节, 了解植物的繁殖特征是解释植物生态适应性和制定有效管理措施的重要依据。该研究以荒漠草原猪毛蒿(Artemisia scoparia)种群为研究对象, 通过测定不同土壤类型的理化性质和猪毛蒿的繁殖特征, 以期探讨影响其繁殖特征的主要土壤驱动因子。结果表明: 灰钙土、风沙土和基岩风化残积土的水溶性碳含量、全氮含量、全磷含量、全盐含量、土壤水分含量、土壤硬度存在显著差异。猪毛蒿平均个体大小、单株头状花序的平均质量和数量均以灰钙土生境下最大, 基岩风化残积土最小。繁殖分配在不同土壤类型下无显著差异, 但与单个头状花序质量、单株头状花序数量和质量间呈极显著正相关关系。单株头状花序数量与单个头状花序质量间呈负相关关系。在风沙土生境下, 单株头状花序质量主要受到土壤水溶性碳含量、土壤水分含量以及pH值的共同影响; 单株头状花序数量受全盐含量的影响最大; 繁殖分配和单个头状花序质量主要受全碳含量的影响。灰钙土生境下, 单株头状花序质量与土壤水溶性碳含量、土壤水分含量和有机碳含量呈正相关关系; 速效氮含量显著影响着单株头状花序数量。而基岩风化残积土生境下, 繁殖特征的变异主要受到土壤水溶性碳含量、土壤硬度、土壤水分含量、全磷和速效磷含量的影响。综合分析发现, 土壤因子对猪毛蒿繁殖特征的影响程度不同, 其中单株头状花序数量和质量极显著地受到土壤水溶性碳含量和土壤水分含量的影响, 繁殖分配和单个头状花序质量与土壤水溶性碳含量、土壤水分含量呈负相关关系。因此, 土壤水溶性碳含量和土壤水分是荒漠草原地区影响猪毛蒿种群繁殖特征的主要土壤因子。     

基于年降水、生长季降水和生长季蒸散的高寒草地水分利用效率

水分利用效率是深入理解生态系统碳、水循环间耦合关系的重要指标。以前研究青藏高原的水分利用效率多基于年降水量(AP)来分析, 但植物对水分的利用主要在生长季。该研究采用以AP、生长季降水量(GSP)和生长季蒸散量(ET_gs)分别计算的年降水利用效率(PUE_a)、生长季降水利用效率(PUE_gs)和生长季水分利用效率(WUE_gs), 分析了2000-2010年间青藏高原两种主要植被类型高寒草甸和高寒草原PUE_a、PUE_gs和WUE_gs的差异及其与降水量、蒸散量和气温的关系。结果表明: (1)高寒草甸的PUE_a、PUE_gs均大于高寒草原, 但两种草地类型的WUE_gs无显著差别, 这说明两种草地类型可能存在相似的内在的水分利用效率。(2)从年际动态来看, PUE_a和PUE_gs的波动范围相似, 而WUE_gs的波动范围更大, 说明以蒸散为依据的WUE_gs可能比PUE_a和PUE_gs更敏感, 因而可能更好地反映生态系统的水分利用能力。(3)高寒草甸和高寒草原的PUE_a、PUE_gs和WUE_gs分别与AP、GSP和ET_gs呈单调递减趋势, 表明3种水分利用效率均随降水量或蒸散量的增加而降低。高寒草原的3种水分利用效率中仅WUE_gs随着气温的增加而增加, 而高寒草甸的3种水分利用效率均与气温无显著关系, 这说明相比高寒草甸, 高寒草原的水分利用效率对气温更加敏感。     

Stimulation of shoot elongation in Salix pentandra by gibberellin A9; activity appears to be dependent upon hydroxylation to GAl via GA20

Cessation of shoot elongation in seedlings of Salix pentandra L. is induced by short photoperiod. Gibbereliin A₉ (GA₉) applied either to the apical bud or injected into a mature leaf, induced shoot elongation under a short photoperiod of 12 h, and GA₉ could completely substitute for a transfer to a long photoperiod. When [³H]GA₉ or [²H₂]GA₉ was injected into a leaf, no [³H]GA₉ was detected in the elongating apex and only traces of [³H]GA₉ were found in the shoot above the treated leaf. By the use of gas chromatography-mass spectrometry (GC-MS), [²H₂]GA₂₀ was identified as the main metabolite of [²H₂]GA₉ in both the shoot and the treated leaf. In addition, [²H₂]GA₁ and [²H₂]GA₂₉ were also identified as metabolites of [²H₂]GA₉. These results are consistent with the hypothesis that exogenous GA, promotes shoot elongation in Salix through its metabolism to GA₂₀ and GA,.     

Azimuthal variation in nighttime sap flow and its mainly influence factors of Populus tomentosa

为明确毛白杨(Populus tomentosa)不同方位夜间蒸腾量(Nt)及茎干充水量(Sr)等夜间液流活动的规律, 探究不同方位Nt和Sr的主要影响因子, 该研究使用热扩散的方法监测了宽窄行模式下栽植的毛白杨茎干不同方位夜间液流, 并用图像法区分Nt和Sr。使用自动气象站和机械式张力计监测太阳总辐射(R_s, kW·m^-2)、空气温度(T_a, ℃)、空气相对湿度(RH, %)、风速(v, m·s^-1)、土壤水势(ψ, kPa)等环境因子。通过比较各方位的Nt和Sr等液流活动的大小情况及其与环境因子之间的相关性得到方位间夜间液流的差异性以及各方位夜间液流的主要影响因子。结果显示: 宽行距位于东侧的样树西方位的Nt和Sr均最大, 其中西方位的Sr显著大于其他3个方位; 北方位的Nt显著小于其他3个方位; 其他方位间的Nt和Sr无显著差异; 各方位夜间茎干充水量占夜间液流量的比例(Sr/Q)无显著差异。宽行距位于西侧的样树西方位的Nt和Sr亦均最大, 其中西方位的Sr显著大于东方位和南方位; 南方位的Nt最小, 显著小于西方位和北方位, 其他方位间的Nt和Sr无显著差异; 南方位的Sr/Q显著大于其他3个方位。各方位的Nt和Sr均与水汽压亏缺(VPD)有显著的正相关关系, 部分方位Nt和Sr与T_a和RH有显著相关关系, 没有任何方位Nt和Sr与v和ψ有显著相关关系。Nt和Sr方位间的差异(Nt_CV、Sr_CV)与VPD、T_a、RH、v和ψ均无显著相关关系。此外, Sr受白天的液流活动的影响显著。综上所述, 毛白杨不同方位Nt和Sr等液流活动具有较大的差异, 且西方位是优势方位; VPD是影响各方位Nt和Sr的主要气象因子。     

不同光脉冲方案对光下最大荧光参数及其计算参数的影响

光下最大荧光(F_m′)是植物生理生态研究中的重要参数,一般采用饱和脉冲(RF)方案来估计.然而,光系统Ⅱ(PSⅡ)受体库的反馈调节会影响RF方案对F_m′估计的准确性.为消除PSⅡ受体库反馈调节的影响,根据光脉冲强度(Q′)与叶绿素荧光(F′)的线性关系提出多相脉冲(MPF)方案,估算Q′无穷大时的F′(即F_m′).本研究采用MPF和RF方案分别对苦槠、青冈和乌桕3个树种叶片的叶绿素荧光和气体交换数据进行同步测量,并对两种方案估计的F_m′及其计算参数PSⅡ光化学效率(Φ_PSII)、PSⅡ的电子传递速率(J)、最大电子传递速率(J_max)、叶肉导度(g_m)和叶绿体内CO₂浓度(C_c)等光合参数进行比较,分析两种方案对3个树种叶片6个光合参数的影响.结果表明: 当光合有效辐射(PAR)<200 μmol·m^-2·s^-1时,两种方案对苦槠、青冈和乌桕叶片F_m′、Φ_PSII和J的估计无显著影响;当PAR>200 μmol·m^-2·s^-1时,采用MPF方案获得的苦槠、青冈和乌桕的F_m′分别比RF方案获得的F_m′高3.5%～5.2%、11.7%～18.0%和3.2%～7.1%;当PAR>200 μmol·m^-2·s^-1时,采用MPF方案获得的Φ_PSII、J和J_max分别不同程度地大于RF方案获得的参数,g_m和C_c分别不同程度地小于RF方案获得的参数.说明当PAR较低(<200μmol·m^-2·s^-1)时,MPF与RF方案对植物叶片F_m′、Φ_PSII、J的估计没有显著影响;当PAR较高(≥200μmol·m^-2·s^-1)时,MPF与RF方案对植物叶片F_m′、Φ_PSII、J、J_max、g_m和C_c的估计有显著影响,且RF方案对植物叶片的F_m′、Φ_PSII、J和J_max比MPF方案分别有不同程度的低估,对g_m和C_c则有不同程度的高估.     

针叶树病原菌异担子菌属的物种多样性及相关检疫建议

异担子菌属Heterobasidion种类是北半球针叶树最严重的森林病原菌,在世界范围内能侵染27种针叶树,对欧洲和北美洲的经营林己造成重大损失.基于传统形态学研究,认为异担子菌属有2个种,即多年异担子菌H.annosum和岛生异担子菌H.insulare,然而单孢交配实验研究证明2个种为复合种.分子系统发育分析研究表...     

Sodium ion transport in Neurospora crassa

Na⁺ influx and efflux in Neurospora crassa RL21a can be studied separately to calculate net Na⁺ movements. In the absence of external K⁺, Na⁺ influx was independent of the K⁺ content of the cells, but when K⁺ was present, the inhibition of Na⁺ influx by external K⁺ was higher the higher the K⁺ content. Efflux depended on the K⁺ and Na⁺ content, and on the history of the cells. Efflux was higher the higher the Na⁺ and K⁺ contents, and, in low-K⁺ cells, the efflux was also higher in cells grown in the presence of Na⁺ than when Na⁺ was given to cells grown in the absence of Na⁺. Addition of K⁺ to cells in steady state with external Na⁺ resulted in a net Na⁺-loss. In cells grown without Na⁺ this loss was a consequence of the inhibition of Na⁺ influx. In Na⁺-grown cells, addition of K⁺ inhibited Na⁺ influx and increased Na⁺ efflux.     

Regulation of nitrate uptake into Chara corallina cells via NH+4 stimulation of NO−3 efflux

Abstract. Net NO₃ uptake by NO⁻₃ deficient Chara cells was used to calculate [NO⁻₃]_c assuming that the cytoplasm occupies 10% total volume and that nitrate reduction and storage are negligible (i.e. maximum [NO⁻₃]_c was calculated). A linear relationship was found between NO⁻₃ efflux and [NO⁻₃]_c. There was an initial burst of NO⁻₃ efflux when NH⁺₄ was added, followed by a slower efflux rate which matched influx rate such that net NO⁻₃ uptake was zero. Over 50% of NO⁻₃ that had been taken up in 2 h was lost within the first 5 min of NH⁺₄ addition. The Nernst equation was used to predict the direction of the electrochemical driving force for NO⁻₃ entry. Under the experimental conditions used NO⁻₃ efflux is actively transported. The differential involvement of both NO⁻₃ influx and NO⁻₃ efflux in the regulation of NO⁻₃ uptake is discussed and a model is proposed to account for these results which envisages discrete NO⁻₃ influx and NO⁻₃ efflux carriers.     

沙地樟子松带状混交林土壤碳氮磷化学计量特征

探究不同沙地樟子松混交林土壤碳氮磷化学计量变化规律,为其混交经营提供科学依据.以沙地樟子松纯林为对照,在沙地樟子松×榆树及沙地樟子松×怀槐带状混交林中,沿沙地樟子松和伴生树种两个方向在距离混交中心0、1、2、3和4 m处的不同土层采集土样,分析土壤有机C、全N、全P、速效N、速效P含量及其计量比的特征.结果表明: 沙地樟子松混交林土壤有机C、全N和速效N含量高于纯林, 沙地樟子松与榆树混交主要增加了深层土壤有机C和全N含量,以及C/N和C/P, 沙地樟子松与怀槐混交提高了土壤N含量, 降低了P含量.随着远离混交林中心,沙地樟子松×榆树混交林中沙地樟子松林带的土壤C/N先升高后降低,全P和速效P含量下降,N/P增加;榆树林带土壤C/N下降,速效P含量先升高后降低.沙地樟子松×怀槐混交林土壤全N含量在沙地樟子松林带先降低后升高,在怀槐林带先升高后降低.沙地樟子松混交林提高了土壤C、N储量,沙地樟子松应与榆树行间混交,与怀槐间隔2行混交.     

黑沙蒿光合能量分配组分在生长季的相对变化与调控机制

为了探明典型荒漠灌木优势物种黑沙蒿(俗名油蒿, Artemisia ordosica)光合过程能量中分配对环境波动的相对变化及其长期调节机制, 该研究于2018年4-10月在宁夏盐池毛乌素沙地, 同时使用MONITORING-PAM多通道荧光监测仪和LI-6400XT便携式光合测量仪对黑沙蒿叶片的最小荧光产量(F_o)、最大荧光产量(F_m)、稳态荧光产量(F_s)、光下最大荧光产量(F_m′)、净光合速率(P_n)、暗呼吸速率(R_d)、蒸腾速率(E)和叶片气孔导度(g_s)进行现场测定, 在实验室内计算比叶面积(SLA)、单位面积氮含量(N_area)、叶绿素含量(C_Chl)和叶绿素a/b (Chl a/b), 分析黑沙蒿光合过程能量分配中固碳耗能占比(Φ_A)、光呼吸耗能占比(Φ_PR)、调节性热耗散耗能占比(Φ_NPQ)和非调节性热耗散耗能占比(Φ_NO)与环境参数和叶性状参数之间的关系以及能量分配各组分之间的相对变化。结果表明, 光化学反应组分(Φ_A、Φ_PR)和热耗散组分(Φ_NPQ、Φ_NO)之间呈负相关竞争关系, 两组分内部呈正相关协同关系, E和Φ_A、Φ_PR正相关, 和Φ_NPQ、Φ_NO负相关。在低土壤含水量(SWC)和高饱和水汽压差(VPD)环境条件下, 黑沙蒿Φ_A、Φ_PR和SLA显著降低, Φ_NPQ和Φ_NO显著增加。研究认为, 在长期干旱或高蒸散条件下, 黑沙蒿通过降低SLA等途径避免水分的过度流失, 同时将部分过剩光能由光呼吸代谢途径转移到热耗散组分进行耗散。波动环境下黑沙蒿形态性状的变异和光合过程能量分配的长期调节机制, 反映了其利用形态与生理的协同可塑性对逆境的适应。     

Root ammonium transport efficiency as a determinant in forest colonization patterns: an hypothesis

Ratios of ammonium (NH₄⁺) to nitrate (NO₃^–) in soils are known to increase during forest succession. Using evidence from several previous studies, we hypothesize that a malfunction in NH₄⁺ transport at the membrane level might limit the persistence of early successional tree species in later seral stages. In those studies, ¹³N radiotracing was used to determine unidirectional fluxes and pool sizes of NH₄⁺ and NO₃^– in seedlings of the late-successional species white spruce ( Picea glauca ) and in the early successional species Douglas-fir ( Pseudotsuga menziesii var. glauca ) and trembling aspen ( Populus tremuloides ). At high external NH₄⁺, the two early successional species accumulated excessive NH₄⁺ in the root cytosol, and exhibited high-velocity, low-efficiency (15% to 22%), membrane fluxes of NH₄⁺. In sharp contrast, white spruce had low cytosolic NH₄⁺ accumulation, and lower-velocity but much higher-efficiency (65%), NH₄⁺ fluxes. Because these divergent responses parallel known differences in tolerance and toxicity to NH₄⁺ amongst these species, we propose that they constitute a significant driving force in forest succession, complementing the discrimination against NO₃^– documented in white spruce (Kronzucker et al. 1997).     

The influences of calcium and magnesium ions on the exchange of monovalent cations in Neurospora crassa

Low-K⁺, high-Na⁺ cells of strain RL21a of Neurospora crassa , in steady state with 25 m M Na⁺, were used to study K⁺/Na⁺ exchanges in the presence or absence of Ca²⁺ and Mg²⁺. In the presence of Ca²⁺ and Mg²⁺, a low concentration of K⁺ (0.3 m M ) triggered a rapid exchange, but in the absence of the divalents, a high K⁺ concentration (30 m M ) was required to initiate the exchange at a rapid rate. In the absence of Ca²⁺ and Mg²⁺, K⁺ uptake did not occur at low K⁺ concentration, internal K⁺ did not regulate Na⁺ influx in the presence of external K⁺, and the efflux of Na⁺ proceeded at maximum activity at very low-K⁺ contents.     

甲型H1N1流感病毒在季流病毒、禽流感病毒共感染时变异可能性的验证

目的 甲型H1N1流感病毒A/California/7/2009分别与A/Brisbane/10/07和A/ShenZhen/406H/06共感染小型香猪,预测甲流病毒在与季流H3N2病毒/甲流病毒与禽流感病毒共感染时是否会发生变异.方法 分别将A/California/7/2009(CA7)与A/Brisbane/10/07(H3N2),A/California/7/2009与A/Shenzhen/406H/06(H5N1)对5～6月龄小型猪共感染,小型猪经复方氯胺酮0.1 mL/kg麻醉后进行滴鼻感染,感染后第5天安乐死动物,取动物肺组织作病毒测序分析.结果 A/California/7/2009(CA7)与A/Brisbane/10/07(H3N2)共感染后,A/California/7/2009病毒PB1基因993位G→A突变,PA基因1659位G→A突变,没有氨基酸的变异.A/California/7/2009与A/Shenzhen/406H/06(H5N1)共感染后A/California/7/2009病毒PB2基因1711位T→C突变.碱基的突变未引起氨基酸的变异.结论 A/California/7/2009(CA7)与A/Brisbane/10/07(H3N2),A/California/7/2009与A/Shenzhen/406H/06(H5N1)共感染后在猪的体内没有发生病毒重组、变异.     

The inhibition of the carbon concentrating mechanism of the green alga Chlorella saccharophila by acetazolamide

The effects of the carbonic anhydrase (CA) inhibitors acetazolamide (AZ) and dextran-bound sulfonamide (DBS) on HCO₃⁻-dependent O₂ evolution in Chlorella saccharophila were evaluated. Addition of 4 μ M AZ or 0.4 mg ml⁻¹ DBS to photosynthesizing cells reduced the O₂ evolution rate at low dissolved inorganic carbon (DIC) concentration, decreased the size of the intracellular acid-labile carbon pool, and decreased the apparent affinity of the cells for DIC. Measurement of the whole-cell affinity of cells for CO₂ and HCO₃⁻ in the presence and absence of inhibitors indicated that active HCO₃⁻ transport was inhibited by AZ and DBS. The inhibition of HCO₃⁻ transport was independent of the inhibition of external and internal CA. These results suggest that the active uptake of HCO₃⁻ occurs initially by the interaction of HCO₃⁻ and a CA-like transporter.     

Proton pumping pyrophosphatase from higher plant mitochondria

In higher plant cells, there are some enzymes capable of utilizing pyrophosphate (PP_i) as an energy donor. Among these, membrane-bound proton pumping pyrophosphatases (H⁺-PP_iase) have been identified. In addition to the well-known vacuolar H⁺-PP_iase (V-PP_iase), there is evidence for the presence of a mitochondrial H⁺-PP_iase. This enzyme is localized on the inner surface of the inner membrane and catalyzes the specific hydrolysis of PP_i, coupled to proton transport, with a H⁺/PP_i stoichiometry of ca 2. This activity is Mg²⁺-requiring, is stimulated by monovalent cations, and is inhibited by Ca²⁺, F⁻ and diphosphonates. The H⁺-PP_iase contains a catalytic head which is constituted by a 35-kDa protein which is loosely bound to the inner membrane. This protein exhibits a PP_iase activity, stimulated by phospholipids, with characteristics very similar to the membrane-bound enzyme. The mitochondrial PP_iase is distinct from the V-PP_iase, because an antibody raised against the 35-kDa protein does not react with tonoplast membranes. The mitochondrial H⁺-PP_iase seems to have an F-type structure, similar to the F-ATP synthase and the membrane-bound PP_iases from mammalian and yeast mitochondria. It is suggested that, beside synthesizing PP_i, this enzyme may act as a buffer for the electrochemical proton gradient, by hydrolyzing PP_i, during conditions of oxygen deprivation.     

Effects of Surfactant Protein-A on the Interaction of Pneumocystis murina with its Host at Different Stages of the Infection in Mice

ABSTRACT. We examined the effects of surfactant protein A (SP-A), a collectin, on the interaction of Pneumocystis murina with its host at the beginning, early to middle, and late stages of infection. Pneumocystis murina from SP-A wild-type (WT) mice inoculated intractracheally into WT mice (WT_S-WT_R) adhered well to alveolar macrophages, whereas organisms from SP-A knockout (KO) mice inoculated into KO mice (KO_S-KO_R) did not. Substitution of WT mice as the source of organisms (WT_S-KO_R) or recipient host macrophages (KO_S-WT_R) restored adherence to that found with WT_S-WT_R mice. In contrast, when immunosuppressed KO and WT mice were inoculated with P. murina from a homologous source (KO_S-KO_R, WT_S-WT_R) or heterologous source (WT_S-KO_R, KO_S-WT_R) and followed sequentially, WT_S-KO_R mice had the highest levels of infection at weeks 3 and 4; these mice also had the highest levels of the chemokine macrophage inflammatory protein-2 and neutrophils in lavage fluid at week 3. Surfactant protein-A administered to immunosuppressed KO_S-KO_R mice with Pneumocystis pneumonia for 8 wk as a therapeutic agent failed to lower the organism burden. We conclude that SP-A can correct the host immune defect in the beginning of P. murina infection, but not in the middle or late stages of the infection.     

Isolation, characterization, and nitrification potential of a methylotroph and two heterotrophic bacteria from a consortium showing methane-dependent nitrification

Abstract A methanotrophic nitrifying consortium was previously obtained from a humisol which showed CH₄-dependent nitrification. Although the methanotroph could not be obtained in pure culture, three other members of the consortium have been isolated: An obligately methylotrophic Methylobacillus (Is-1) which grows only on CH₃OH and does not nitrify; a Pseudomonas (Is-2) which grows on Is-1 culture filtrate and produces NO₂⁻, NO₃⁻ and N₂O from NH₂OH, and NO₃⁻ from NO₂⁻; and a second Pseudomonas (Is-3) which produces NO₃⁻ from NH₄⁺ or NO₂⁻, and N₂O from NH₂OH. A model is proposed for the trophic relations and nitrogen transformations in the consortium which may apply to some natural systems.     

The role of Mg2+ in proton transport by the tonoplast pyrophosphatase in Riccia fluitans vacuoles

The Mg²⁺-dependent activity of the tonoplast pyrophosphatase (PPase) was investigated by measuring proton transport and by using the acridine orange technique on intact vacuoles of the aquatic liverwort Riccia fluitans L. In solutions with both Mg²⁺ and pyrophosphate present, a number of complexes are formed, which could all influence the enzymatic and hence the transport activity of the PPase. Therefore, the individual concentrations of these complexes were calculated and their contributions to proton transport across the tonoplast were tested. From these experiments we conclude that Mg²⁺ has three different roles: (i) Mg²⁺ stimulates transport activity of the PPase. (ii) Mg₂PP_i inhibits PPase-mediated H⁺ transport, (iii) MgPP_i* (= MgPP_i^2-+ MgHPP_i^-) is the substrate with an apparent K_1/2= 5–10 μM, with no discrimination between MgPP_i^2- and MgHPP_i^-.