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1.
The activating or inhibiting actions of a variety of anion species and of oligomycin, aurovertin and Dio-9 on the ATPase of a sonic particle preparation of rat liver mitochondria have been characterized by measurements of the relevantV
max,K
i
andK
m
values.The normalV
max was increased by a factor near 7 by the anions: dichromate, chromate, pyrophosphate, orthophosphate, orthoarsenate and sulphate. The fully activating concentration varied from about 2 mM for dichromate to 150 mM for sulphate. The increase inV
max was accompanied by a time-dependent decrease in (K
i)ADP, but there was no change in (K
m)ATP. The increase inV
max by the activating anions was abolished by aurovertin; but in presence of oligomycin, the lowV
max was increased by the activating anions by the same factor as theV
max in absence of oligomycin.Certain anions, notably azide, decreasedV
max, but did not affect (K
i)ADP or (K
m)ATP. The decrease inV
max by azide and oligomycin were approximately additive. Even at high concentration, Dio-9 was without detectable effect on the ATPase, but it had a gramicidinlike effect on the intact mitochondria.The specificity of the ATPase for ATP relative to GTP was found to be attributable to the high value of (V
max)ATP compared with (V
max)GTP. The values of (K
m)ATP and (K
m)GTP were virtually the same.Some rationalization of these and other supporting observations is attempted in terms of present knowledge of the constitution of the ATPase complex. 相似文献
2.
Yusuke Mizokami Ko Noguchi Mikiko Kojima Hitoshi Sakakibara Ichiro Terashima 《Plant, cell & environment》2019,42(4):1257-1269
C3 photosynthesis is often limited by CO2 diffusivity or stomatal (gs) and mesophyll (gm) conductances. To characterize effects of stomatal closure induced by either high CO2 or abscisic acid (ABA) application on gm, we examined gs and gm in the wild type (Col‐0) and ost1 and slac1‐2 mutants of Arabidopsis thaliana grown at 390 or 780 μmol mol?1 CO2. Stomata of these mutants were reported to be insensitive to both high CO2 and ABA. When the ambient CO2 increased instantaneously, gm decreased in all these plants, whereas gs in ost1 and slac1‐2 was unchanged. Therefore, the decrease in gm in response to high CO2 occurred irrespective of the responses of gs. gm was mainly determined by the instantaneous CO2 concentration during the measurement and not markedly by the CO2 concentration during the growth. Exogenous application of ABA to Col‐0 caused the decrease in the intercellular CO2 concentration (Ci). With the decrease in Ci, gm did not increase but decreased, indicating that the response of gm to CO2 and that to ABA are differently regulated and that ABA content in the leaves plays an important role in the regulation of gm. 相似文献
3.
ABA stimulation of outward K+ current (I
K,out) in Vicia faba guard cells has been correlated with a rise in cytosolic pH (pH
i
). However, the underlying mechanism by which I
K,out is affected by pH
i
has remained unknown. Here, we demonstrate that pH
i
regulates outward K+ current in isolated membrane patches from Vicia faba guard cells. The stimulatory effect of alkalinizing pH
i
was voltage insensitive and independent of the two free calcium levels tested, 50 nm and 1 μm. The single-channel conductance was only slightly affected by pH
i
. Based on single-channel measurements, the kinetics of time-activated whole-cell current, and the analysis of current noise
in whole-cell recordings, we conclude that alkaline pH
i
enhances the magnitude of I
K,out by increasing the number of channels available for activation. The fact that the pH
i
effect is seen in excised patches indicates that signal transduction pathways involved in the regulation of I
K,out by pH
i
, and by implication, components of hormonal signal transduction pathways that are downstream of pH
i
, are membrane-delimited.
Received: 5 June 1996/Revised: 1 August 1996 相似文献
4.
Prostaglandins are important in signaling pathways involved in modulating the rates of Na+ transport in a diverse group of tissues possessing apical membrane epithelial channels. PGE2 is known to cause either stimulation, inhibition or transient stimulatory changes of Na+ transport. We have continued our studies of frog skins that are known to respond to forskolin and PGE2 with large steady-state increases of transport and have used noninvasive methods of blocker-induced noise analysis of Na+ channels to determine their channel densities (N
T
) and open probabilities (P
o
). In the absence of exogenous hormones, baseline rates of Na+ transport are especially high in scraped skins (R. pipiens pipiens) studied in the fall of the year. Na+ transport was inhibited by indomethacin and by removal of the unstirred layers of the corium (isolated epithelia) alone suggesting
that PGE2 is responsible for the sustained and elevated rates of transport in scraped skins. Changes of transport caused by indomethacin,
forskolin or PGE2 were unquestionably mediated by considerably larger changes of N
T
than compensatory changes of P
o
. Since cAMP caused no change of P
o
in tissues pretreated with indomethacin, PGE2 appears in this tissue to serve a dual role, increasing the steady state N
T
by way of cAMP and decreasing P
o
by unknown mechanisms. Despite appreciable PGE2-related decreases of P
o
, the net stimulation of transport occurs by a considerably greater cAMP-mediated increase of N
T
.
Received: 28 February 1996/Revised: 22 August 1996 相似文献
5.
Two transport systems for glucose were detected: a high affinity system with a Km of 27 μM, and a low affinity system with a Km of 3.3 mM. The high affinity system transported glucose, 2-deoxy-d-glucose (Km = 26 μM), 3-O-methylglucose (Km = 19 μM), d-glucosamine (Km = 652 μM), d-fructose (Km = 2.3 mM) and l-sorbose (Km = 2.2 mM). All sugars were accumulated against concentration gradients. The high affinity system was strongly or completely inhibited by N-ethylmaleimide, quercetin, 2,4-dinitrophenol and sodium azide. The system had a distinct pH optimum (7.4) and optimum temperature (45°C). The low affinity system transported glucose, 2-deoxy-d-glucose (Km = 7.5 mM), and 3-O-methylglucose (Km = 1.5 mM). Accumulation again occurred against a concentration gradient. The low affinity system was inhibited by N-ethylmaleimide, quercetin and 2,4-dinitrophenol, but not by sodium azide. The rate of uptake by the low affinity system was constant over a wide temperature range (30–50°C) and was not much affected by pH; but as the pH of the medium was altered from 4.5 to 8.9 a co-ordinated increase in affinity for 2-deoxy-d-glucose (from 52.1 mM to 0.3 mM) and decrease in maximum velocity (by a factor of five) occurred. Both uptake systems were present in sporelings germinated in media containing sodium acetate as sole carbon source. Only the low affinity system could initially be demonstrated in glucose-grown tissue, although the high affinity system was restored by starvation in glucose-free medium. The half-time for restoration of high affinity activity was 3.5 min and the process was unaffected by cycloheximide. Addition of glucose to an acetate-grown culture inactivated the high affinity system with a half-life of 5–7.5 s. Addition of cycloheximide to an acetate-grown culture caused decay of the high affinity system with a half-life of 80 min. Regulation is thus thought to depend on modulation of protein activity rather than synthesis, and the kinetics of glucose, 2-deoxy-d-glucose and 3-O-methylglucose uptake would be consistent with there being a single carrier showing negative co-operativity. 相似文献
6.
In aqueous solutions of the amylase–iodine complex the concentration of free iodine [If]v after reaching equilibrium (or closely approximating it) is determined by the following factors: temperature, pH, concentration of iodide ions and amylose, and DP of amylose. In the present paper the role of temperature, amylose concentration, and DP has been investigated. At half-saturation of amylose by iodine, the reciprocal value of free iodine defines the equilibrium constant: 1/[If]v = K. The relation between [If]v, in normality and temperature is the following: 5 + log [If]v = ?(2.132/T) + 8.52, for DP n = 1290, 0.4 mg. amylose in 100 ml. 0.1N HCl. The value of the energy of activation Ea between 2 and 52°C. is 9.72 kcal./mole. The influence of amylose concentration [Am] on photometrically determined [If]v, at 20°C, in the range of 0.1–1.2 mg./100 ml. 0.1 N HCl for DP n = 1290 is: 5 + log [If]v = 0.209 ? 0.047 log [Am]. At [Am] = 0.6 mg. amylose/ 100 ml. 0.1 N HCl and 20°C, the value of [If]v depends on DP n as follows: 5 + log [If]v = 0.085 = + 0.222 log (104/DP n). These above equations are summarized by the relation: [If]v = exp {16.865 ? (Ea/RT)}[Am]0.047(104/DP n)0.222 ×10?5 Considering that the determination of [If]v by automatic photometric titration can be performed quickly and with appropriate reproducibility, this method is convenient for a rapid empirical and approximate determination of DP of amylose on a microscale. The iodine-binding capacity [IBC] as well as the value of λmax, have been also investigated as functions of DP n, by photometric and by amperometric titration. 相似文献
7.
C. E. Smalley E. M. Tucker P. B. Dunham J. C. Ellory 《The Journal of membrane biology》1982,64(3):167-174
Summary Antibodies of two specificities in alloimmune sheep anti-L sera, anti-L
P
and anti-L
l
, were separated by a new technique and characterized. Absorption of anti-L serum with trypsinized LK (LL) sheep red cells left anti-L
P
antibodies; the absorbed anti-L
l
antibodies were then eluted. Anti-L
P
was only weakly lytic in the presence of complement; it had no effect on passive K influx, but stimulated active K influx. The stimulation could be reversed by eluting the antibody in glycine buffer at low pH. Stimulatory activity in the eluted cells could be restored by resensitization with anti-L
P
. Anti-L
l
was more strongly lytic than anti-L
P
in the presence of complement; it had no effect on active K influx, but inhibited passive K influx. Pig anti-ruminant IgG conjugated to hemocyanin was used to visualize by electron microscopy the number of L
P
and L
l
antigen sites onLL sheep red cells sensitized with anti-L
P
and anti-L
l
. The values obtained were 590 L
P
sites/cell and 847 L
l
sites/cell. 相似文献
8.
The structural properties of oligonucleotides containing two different types of G-rich sequences at the 3′-ends were compared. It is shown that oligonucleotides with uninterrupted runs of guanine residues at the 3′-end, e.g., d(T15G12), form multistranded structures stabilized by guanine-guanine interactions. The chemical and physical properties of these complexes differ from those of the complexes formed by oligonucleotides with telomere-like sequences, e.g., d(T15G4T2G4). In methylation protection and methylation interference experiments, we found all the guanines in complexes formed by d(T15G15) and d(T15G12) to be accessible to methylation. Furthermore, the methylated monomers retain the ability to polymerize. This contrasts with the inaccessibility of the guanines in d(T15G4T2G4) to methylation and the inability of the methylated monomer to form supramolecular structures. The stoichiometry of the complexes arising from the two types of oligonucleotides also differs. The complexes formed by d(T15G15) consist of consecutive integer numbers of DNA strands, whereas complexes formed by telomere-like oligonucleotides contain 1, 2, 4, or multiples of four strands. Magnesium ions favor formation of high molecular weight complexes by d(T15G15) and d(T15G12), but not by d(T15G4T2G4). The d(T15G15) and d(T15G12) complexes have very high thermal stability compared with telomeric complexes. However, at low temperatures, the thymine bases within the telomeric motif, TTGGGGTTGGGG, appear to allow for the formation of stable high-molecular weight species with a longer nonguanine portion. © 1998 John Wiley & Sons, Inc. Biopoly 45: 427–434, 1998 相似文献
9.
10.
Leaf CO2 uptake (A) in C4 photosynthesis is limited by the maximum apparent rate of PEPc carboxylation (Vpmax) at low intercellular [CO2] (ci) with a sharp transition to a ci-saturated rate (Vmax) due to co-limitation by ribulose-1:5-bisphosphate carboxylase/oxygenase (Rubisco) and regeneration of PEP. The response of A to ci has been widely used to determine these two parameters. Vmax and Vpmax depend on different enzymes but draw on a shared pool of leaf resources, such that resource distribution is optimized, and A maximized, when Vmax and Vpmax are co-limiting. We collected published A/ci curves in 49 C4 species and assessed variation in photosynthetic traits between phylogenetic groups, and as a function of atmospheric [CO2]. The balance of Vmax-Vpmax varied among evolutionary lineages and C4 subtypes. Operating A was strongly Vmax-limited, such that re-allocation of resources from Vpmax towards Vmax was predicted to improve A by 12% in C4 crops. This would not require additional inputs but rather altered partitioning of existing leaf nutrients, resulting in increased water and nutrient-use efficiency. Optimal partitioning was achieved only in plants grown at pre-industrial atmospheric [CO2], suggesting C4 crops have not adjusted to the rapid increase in atmospheric [CO2] of the past few decades. 相似文献
11.
G. B. Postnikova S. V. Tselikova E. A. Shekhovtsova 《Biochemistry. Biokhimii?a》2009,74(11):1211-1218
The rates of oxygen uptake by rat liver mitochondria (MC) (native coupled, freshly frozen, and uncoupled by FCCP) have been
measured polarographically in the absence (V
0) or presence (V
1) of 0.11–0.25 mM sperm whale MbO2. Under the same standard conditions, the rate of sperm whale MbO2 deoxygenation (V
2) has been studied spectrophotometrically in the presence of respiring MC. For freshly frozen MC, the dependence of V
1 and V
2 on the overall charge of MbO2 has been investigated at pH 5.6–7.6, and the influence of other differently charged proteins (apomyoglobin, egg lysozyme,
lactalbumin, and BSA) has been studied at pH 7.4. It is shown that the rate of mitochondrial respiration in the presence of
MbO2 increases by 10–30% (V
1 > V
0). No myoglobin effect is observed for FCCP-uncoupled MC (V
max does not change). The rate of MbO2 deoxygenation is equal to the rate of oxygen uptake by mitochondria (V
2/V
1 ∼ 1 at pH 7.2–7.5). At varying pH < 7.2, the V
2 values become markedly higher than V
1, evidently due to the increased MbO2 positive charge and its stronger interaction with negatively charged mitochondrial membrane. At pH 7.4, on the contrary,
V
2 is twice lower than V
1 in the case of negatively charged CM-MbO2 (pI 5.2), which has carboxymethylated histidines. Positively charged lysozyme (pI 11) strongly inhibits MbO2 deoxygenation (V
2) without affecting oxygen uptake by MC (V
0 and V
1). At the same time, apomyoglobin (pI 8.5), which is structurally very similar to the holoprotein, and both negatively charged lactalbumin (pI 4.4) and BSA (pI 4.7) have no substantial influence on V
2 and V
1. The MC membrane evidently has no specific sites for the interaction with myoglobin. Rather, the protein contacts with phospholipids
of the outer membrane during MbO2 deoxygenation, and electrostatic interactions are of great importance for this process. 相似文献
12.
Electrophysiological correlates of the perception of emotional stimuli were studied by means of recording the visual evoked
potentials (EP) in 20 derivations (Fz, Cz, Pz, Oz, Fp
1/2,F
3/4,F
7/8,C
3/4,P
3/4,T
3/4,T
5/6, andO
1/2) during the emotional test performance. The performance of a special task by subjects was assessed positively or negatively
(by administering emotionally positive or negative stimuli, respectively). Factor analysis revealed seven factors, which described
the EP component structure. Analysis of variance demonstrated the influence of the emotional stimuli sign on the factorsP
100,P
140,N
160,P
220,P
340, and “slow wave.” Hemispheric difference in reactions to the stimuli of a different emotional sign were recorded. During
presentation of the positive and negative assessments, the amplitudes of the factorsP
100,P
340, and “slow wave” were maximally different in the left hemisphere, while the factorsN
160 andP
220 were maximally different in the right hemisphere. 相似文献
13.
Kunio Koshimura Yasutaka Takagi Soichi Miwa †Tsuneo Kido ‡Yasuyoshi Watanabe Yoshio Murakami Yuzuru Kato Tomoh Masaki 《Journal of neurochemistry》1995,65(2):827-830
Abstract: 6R-l -erythro-Tetrahydrobiopterin (6R-BH4) is a cofactor for aromatic l -amino acid hydroxylases and nitric oxide synthase. Recently, we have reported that independently of its cofactor activities, 6R-BH4 acts from the outside of neurons in the brain to enhance the release of monoamine neurotransmitters such as dopamine. To characterize the pharmacological properties of the action, we examined the effects of 6S-BH4, a diastereoisomer of 6R-BH4, on dopamine release in the rat striatum by using brain microdialysis and compared its effects with those of 6R-BH4. Perfusion of 6S-BH4 or 6R-BH4 through the dialysis probe increased extracellular dopamine levels (an index of in vivo dopamine release) concentration dependently; the maximal increase by 6S-BH4, was one-sixth of that by 6R-BH4. 6S-BH4 increased extracellular DOPA levels in the presence of NSD 1015, an inhibitor of aromatic l -amino acid decarboxylase (an index of in vivo tyrosine hydroxylase activity), to an extent similar to the increase induced by 6R-BH4. The increase in the DOPA levels induced by either of the pteridines was abolished after pretreatment of rats with α-methyl-p-tyrosine (an inhibitor of tyrosine hydroxylase). Under the same conditions, the 6S-BH4-induced dopamine release was abolished, but most of the 6R-BH4-induced increase persisted. Coadministration of 6S-BH4 with 6R-BH4 inhibited the increase in dopamine release induced by 6R-BH4 alone. These results show that 6R-BH4 stimulates dopamine release by acting at the specific recognition site on the neuronal membrane, and that 6S-BH4 acts as an antagonist of 6R-BH4 at this site, although it has cofactor activities. 相似文献
14.
Mesophyll conductance decreases in the wild type but not in an ABA‐deficient mutant (aba1) of Nicotiana plumbaginifolia under drought conditions
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YUSUKE MIZOKAMI KO NOGUCHI MIKIKO KOJIMA HITOSHI SAKAKIBARA ICHIRO TERASHIMA 《Plant, cell & environment》2015,38(3):388-398
Under drought conditions, leaf photosynthesis is limited by the supply of CO2. Drought induces production of abscisic acid (ABA), and ABA decreases stomatal conductance (gs). Previous papers reported that the drought stress also causes the decrease in mesophyll conductance (gm). However, the relationships between ABA content and gm are unclear. We investigated the responses of gm to the leaf ABA content [(ABA)L] using an ABA‐deficient mutant, aba1, and the wild type (WT) of Nicotiana plumbaginifolia. We also measured leaf water potential (ΨL) because leaf hydraulics may be related to gm. Under drought conditions, gm decreased with the increase in (ABA)L in WT, whereas both (ABA)L and gm were unchanged by the drought treatment in aba1. Exogenously applied ABA decreased gm in both WT and aba1 in a dose‐dependent manner. ΨL in WT was decreased by the drought treatment to ?0.7 MPa, whereas ΨL in aba1 was around ?0.8 MPa even under the well‐watered conditions and unchanged by the drought treatment. From these results, we conclude that the increase in (ABA)L is crucial for the decrease in gm under drought conditions. We discuss possible relationships between the decrease in gm and changes in the leaf hydraulics. 相似文献
15.
The sensitivity of Cx45 channels to CO2, transjunctional voltage (V
j) and inhibition of calmodulin (CaM) expression was tested in oocytes by dual voltage clamp. Cx45 channels are very sensitive to V
j and close with V
j preferentially by the slow gate, likely to be the same as the chemical gate. With a CO2-induced drop in junctional conductance (G
j), both the speed of V
j-dependent inactivation of junctional current (I
j) and V
j sensitivity increased. With 40-mV V
j-pulses, the of single exponential I
j decay reversibly decreased by 40% during CO2 application, and Gj steady state/Gj peak decreased multiphasically, indicating that both kinetics and V
j sensitivity of chemical/slow V
j gating are altered by changes in [H+]i and/or [Ca2+]i. CaM expression was inhibited with oligonucleotides antisense to CaM mRNA. With 15 min CO2, relative junctional conductance (G
jt/G
jt0) dropped to 0% in controls, but only by 17% in CaM-antisense oocytes. Similarly, V
j sensitivity was significantly lessened in CaM-antisense oocytes. The data indicate that both the speed and sensitivity of V
j-dependent inactivation of the junctional current of Cx45 channels are affected by CO2 application, and that CaM plays a key role in channel gating. 相似文献
16.
The parameters estimated from traditional A/C
i curve analysis are dependent upon some underlying assumptions that substomatal CO2 concentration (C
i) equals the chloroplast CO2 concentration (C
c) and the C
i value at which the A/C
i curve switches between Rubisco- and electron transport-limited portions of the curve (C
i-t) is set to a constant. However, the assumptions reduced the accuracy of parameter estimation significantly without taking
the influence of C
i-t value and mesophyll conductance (g
m) on parameters into account. Based on the analysis of Larix gmelinii’s A/C
i curves, it showed the C
i-t value varied significantly, ranging from 24 Pa to 72 Pa and averaging 38 Pa. t-test demonstrated there were significant differences in parameters respectively estimated from A/C
i and A/C
c curve analysis (p<0.01). Compared with the maximum ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) carboxylation rate (Vcmax), the maximum electron transport rate (Jmax) and Jmax/Vcmax estimated from A/C
c curve analysis which considers the effects of g
m limit and simultaneously fits parameters with the whole A/C
c curve, mean Vcmax estimated from A/C
i curve analysis (Vcmax-C
i) was underestimated by 37.49%; mean Jmax estimated from A/C
i curve analysis (Jmax-C
i) was overestimated by 17.8% and (Jmax-C
i)/(Vcmax-C
i) was overestimated by 24.2%. However, there was a significant linear relationship between Vcmax estimated from A/C
i curve analysis and Vcmax estimated from A/C
c curve analysis, so was it Jmax (p<0.05). 相似文献
17.
Local reflection coefficients (R) provide important insights into the influence of wave reflection on vascular haemodynamics. Using the relatively new time-domain method of wave intensity analysis, R has been calculated as the ratio of the peak intensities (RPI) or areas (RCI) of incident and reflected waves, or as the ratio of the changes in pressure caused by these waves (RΔP). While these methods have not yet been compared, it is likely that elastic non-linearities present in large arteries will lead to changes in the size of waves as they propagate and thus errors in the calculation of RPI and RCI. To test this proposition, RPI, RCI and RΔP were calculated in a non-linear computer model of a single vessel with various degrees of elastic non-linearity, determined by wave speed and pulse amplitude (ΔP+), and a terminal admittance to produce reflections. Results obtained from this model demonstrated that under linear flow conditions (i.e. as ΔP+→0), RΔP is equivalent to the square-root of RPI and RCI (denoted by RPIp and RCIp). However for non-linear flow, pressure-increasing (compression) waves undergo amplification while pressure-reducing (expansion) waves undergo attenuation as they propagate. Consequently, significant errors related to the degree of elastic non-linearity arise in RPI and RCI, and also RPIp and RCIp, with greater errors associated with larger reflections. Conversely, RΔP is unaffected by the degree of non-linearity and is thus more accurate than RPI and RCI. 相似文献
18.
Minoru Murai 《Population Ecology》1975,16(2):289-308
A model was made to clarify the basic processes of competition to occur among larvae by the exploitation as defined byBakker (1969). It was found that this model is applicable to the experimental results on the food exploitation among Droshophila larvae obtained byBakker (1961). In the model the preimaginal stage is divided into two periods;Tf which is the time that a group of larvae spends in exhausting the food after hatching, and Ts which is the duration of the starvation period after Tf.Tf and then Wl (larval body weight) just after the end of Tf are decided by Fs (amount of food supplied per larva at larval hatching) and Fc (amount of food consumed per larva).Tf affects on the onset of Ts as well as Rl (rate of decrease in the individual body weight during Ts).Wa (weight of emerging adults) is gotten by a subtraction of Rl from Wl just after the end of Tf,Re is affected directly by these components of Wl and Rl. As a result, Wa and Re are expressed by functions of Fs. This model confirmed that the food exploitation lead to the competition of scramble type. Finally it was suggested that there exist some strategies which prevent ill-effects owing to the food exploitation. 相似文献
19.
Lorna E. Street Gaius R. Shaver Edward B. Rastetter Mark T. van Wijk Brooke A. Kaye Mathew Williams 《Global Change Biology》2012,18(9):2838-2852
Arctic vegetation is characterized by high spatial variability in plant functional type (PFT) composition and gross primary productivity (P). Despite this variability, the two main drivers of P in sub‐Arctic tundra are leaf area index (LT) and total foliar nitrogen (NT). LT and NT have been shown to be tightly coupled across PFTs in sub‐Arctic tundra vegetation, which simplifies up‐scaling by allowing quantification of the main drivers of P from remotely sensed LT. Our objective was to test the LT–NT relationship across multiple Arctic latitudes and to assess LT as a predictor of P for the pan‐Arctic. Including PFT‐specific parameters in models of LT–NT coupling provided only incremental improvements in model fit, but significant improvements were gained from including site‐specific parameters. The degree of curvature in the LT–NT relationship, controlled by a fitted canopy nitrogen extinction co‐efficient, was negatively related to average levels of diffuse radiation at a site. This is consistent with theoretical predictions of more uniform vertical canopy N distributions under diffuse light conditions. Higher latitude sites had higher average leaf N content by mass (NM), and we show for the first time that LT–NT coupling is achieved across latitudes via canopy‐scale trade‐offs between NM and leaf mass per unit leaf area (LM). Site‐specific parameters provided small but significant improvements in models of P based on LT and moss cover. Our results suggest that differences in LT–NT coupling between sites could be used to improve pan‐Arctic models of P and we provide unique evidence that prevailing radiation conditions can significantly affect N allocation over regional scales. 相似文献
20.
Cytochrome a
1
c
1 was highly purified from Nitrobacter agilis. The cytochrome contained heme a and heme c of equimolar amount, and its reduced form showed absorption peaks at 587, 550, 521, 434 and 416 nm. Molecular weight per heme a of the cytochrome was estimated to be approx. 100,000–130,000 from the amino acid composition. A similar value was obtained by determining the protein content per heme a. The cytochrome molecule was composed of three subunits with molecular weights of 55,000, 29,000 and 19,000, respectively. The 29 kd subunit had heme c.Hemes a and c of cytochrome a
1
c
1 were reduced on addition of nitrite, and the reduced cytochrome was hardly autoxidizable. Exogenously added horse heart cytochrome c was reduced by nitrite in the presence of cytochrome a
1
c
1; K
m values of cytochrome a
1
c
1 for nitrite and N. agilis cytochrome c were 0.5 mM and and 6 M, respectively. V
max was 1.7 mol ferricytochrome c reduced/min·mol of cytochrome a
1
c
1 The pH optimum of the reaction was about 8. The nitrite-cytochrome c reduction catalyzed by cytochrome a
1
c
1 was 61% and 88% inhibited by 44M azide and cyanide, respectively. In the presence of 4.4 mM nitrate, the reaction was 89% inhibited. The nitrite-cytochrome c reduction catalysed by cytochrome a
1
c
1 was 2.5-fold stimulated by 4.5 mM manganous chloride. An activating factor which was present in the crude enzyme preparation stimulated the reaction by 2.8-fold, and presence of both the factor and manganous ion activated the reaction by 7-fold.Cytochrome a
1
c
1 showed also cytochrome c-nitrate reductase activity. The pH optimum of the reaction was about 6. The nitrate reductase activity was also stimulated by manganous ions and the activating factor. 相似文献