Proton Binding Capacity Research Articles

Chemical and Spectroscopic Characterization of Algae Surfaces

The surfaces of two algae species (Cyclotella cryptica, diatom; Chlamydomonas reinhardtii, green alga) were characterized with regard to their interactions with copper. Chemical and spectroscopic methods (FT-IR, continuous-wave EPR, and two-pulse ESEEM) gave information about the kinds of functional groups (-NH2, R-COOH, R-OH, and Si-OH) on the surfaces of the algae. Maximum proton binding capacities of 9.7 × 10-4 and 9.1 × 10-4 mol/g algae (dry weight) were determined for C. cryptica and C. reinhardtii, respectively. The maximum Cu(II) binding capacity was 7.6 × 10-7 mol/g for the diatom and 6.2 × 10-6 mol/g for the green alga with [Cu2+] = 10-13−10-11 in solution (at pH 6.9). Less than 1% of the total proton binding sites are occupied by copper under these conditions. The high conditional stability constants (log K = 11.9 for C. cryptica and log K = 11.3 for C. reinhardtii, at pH 6.9) demonstrate the strong binding of copper to the algae surfaces. These results are confirmed by the CW-EPR and two-pulse ESEEM spectroscopy, which indicate binding to N-ligands, with histidine being one of the possible ligands for copper. The binding sites on algae surfaces represent a buffer capacity for Cu2+ in natural waters.

Kinetics of dark proton efflux in chloroplasts

The rate constant for dark proton efflux from preilluminated chloroplasts, was found to be proportional to the proton permeability, and inversely proportional to the ‘proton binding capacity’ of the thylakoids (the ratio between bound and free protons). Dark proton efflux was resolved into two kinetically distinct components: a diffusion-mediated process which was predominant below pH 7, and a separate leakage pathway, characterized by linear dependence on the internal to external proton concentration ratio, which was predominant above pH 7. An increased proton-binding capacity accompanied the increased proton permeability associated with this second pathway.

Protonation of Macrocyclic Polyethers

AbstractProton affinity of various “crown” ethers is discussed. Equations are given for simultaneous calculation of the complexation and the dissociation constants from conductivity data. pKf in 1.2‐dichloroethane is 8.6 and 8.3, respectively, for the cis‐syn‐cis and the cis‐anti‐cis isomers of dicyclohexyl‐18‐CR‐6, the most basic among the investigated “crown” ethers. pKf = 8.2 for the mixture of these isomers in acetonitrile (AN). The effect of water on pKf of “crown” ethers in aprotic solvents is discussed. It is suggested that a monohydrate of the “oxonium‐crown” rather than a “hydronium‐crown” may be formed. The proton binding capacity of “crown” ethers may be applied for extraction of acids and in catalysis. Dicyclohexyl‐24‐CR‐8 has been found to be an equally effective extractant for HNO3 as the Dicyclohexyl‐18‐CR‐6.

The effects of 2, 4‐dichIorophenoxyacetk acid altered chloroplast development on photosynthesis

We studied the changes in function and physical properties of isolated radish (Raphonus sativus L. cv. Sparkler) lamellar membranes 48 h after chloroplast development was altered by 2, 4‐(dichlorophenoxy)acet, tc acid. The number of chlorophyll molecules attendant to each electron transport chain was approximately 25% less in the chloroplasts from 2, 4‐(dichlorophenoxy)acetic acid‐treated plants than in chloroplasts from untreated plants. The maximal turnover rate of Photosystem I] in the treated chloroplasts was slightly less than half the turnover rate in normal chloroplasts. The efficiency of coupling between electron flux and ATP formation was not significantly different in the two chloroplast types. This hight efficiency of photophosphorylation in addition to normal membrane conductance to hydrogen ions indicates that the herbicide has not brought about a general deterioration of the membrane. A dramatic increase in the proton binding capacity of the lamellar membrane was observed in the treated chloroplasts. This increase in hydrogen ion buffering groups was largely accounted for by extrinsic membrane proteins bound to the exterior surface of the lamellar membrane. Although the addition of 2, 4‐(dichloro‐phenoxy) acetic acid to chloroplasts isolated from untreated plants caused concurrent uncoupling of ATP formation and inhibition of electron transport, our data show that these direct effects of the compound have little to do with its herbicidal action.

Measurement of chloroplast internal protons with 9-aminoacridine. Probe binding, dark proton gradient, and salt effects

A defined ratio, γ, of the total proton uptake to the concentration change of free internal H + is observed for illuminated envelope-free chloroplasts (Haraux, F. and de Kouchkovsky, Y. (1979) Biochim. Biophys. Acta, 546, 455–471). Proton uptake is measured by the external pH shift, free internal H + by 9-aminoacridine fluorescence quenching. Extension of this work leads to the following conclusions, which, in the case of 9-aminoacridine behaviour, should apply to any kind of diffusible protonizable ΔpH probe: 1. 1. The γ constancy is preserved when the internal volume ( V i) is modulated by chlorophyll and osmolarity changes: thus, 9-aminoacridine behaves as expected from the ΔpH distribution of an amine of high p K; previous doubts on this point are attributed to the lack of control of the external proton uptake. 2. 2. With variable 9-aminoacridine concentration, however, some variation of γ confirms the existence of slight light-induced probe-membrane interactions. 3. 3. According to the diffuse layer theory, salts decrease the negative potential at the ‘plane of closest approach’ of the thylakoids, thereby releasing the excess 9-aminoacridine in this diffuse layer, which increases its fluorescence. Although of equal valency, NH + 4 is more potent than K +, suggesting competition between amines for specific anionic binding sites. 4. 4. Two categories of membrane modifications are induced by salts: in addition to the above-mentioned electrical effect, mono- and divalent cations at high concentration increase the chloroplast proton binding capacity. La 3+ is only able to release the excess dye in the diffuse layer and leaves γ unchanged. Therefore the probe-membrane interactions should have limited importance for steady-state ΔpH measurement. 5. 5. A Donnan-type dark pH difference, which could seriously bias these ΔpH estimates, is found experimentally to be less than 2 (no significant γ change when V i varies) and even theoretically less than 1 (on the basis of the concentration of the non-diffusible internal protonizable groups). Similarly, the predictable errors of V i and its possible light-induced variations must have a small effect on ΔpH under present experimental conditions.

Control of Cell Elongation in Nitella by Endogenous Cell Wall pH Gradients

The multiaxial stress of turgor pressure was stimulated in vitro by inflating isolated Nitella cell walls with mercury. The initial in vitro extension at pH 6.5, 5 atmospheres pressure, returned the wall approximately to the in vivo stressed length, and did not induce any additional extension during a 15-minute period. Upon release of pressure, a plastic deformation was observed which did not correlate with cell growth rates until the final stages of cell maturation. Since wall plasticity does not correlate with growth rate, a metabolic factor(s) is implicated. Walls at all stages of development exhibited a primary yield stress between 0 and 2 atmospheres, while rapidly growing cells (1-3% per hour) exhibited a secondary yield stress of 4 to 5 atmospheres. The creep rate and plastic deformation of young walls were markedly enhanced by acid buffers (10 millimolar, pH </= 5.3).Nitella cells produce acid and base "bands" along their length due to localized excretion of protons and hydroxyl ions. Marking experiments showed that growth is largely restricted to the acid regions. Growth in the acid bands was inhibited by alkaline buffers, and growth in the base bands was stimulated by acidic buffers. The two zones have similar mechanical properties. When the proton-binding capacity of the wall was taken into account, the pH of the solution in contact with inner wall surface in the acid band was estimated to be about 4.3, well within the threshold of acid-enhanced creep. Since the inner 25% of the wall controls extensibility, we conclude that growth in the acid band is caused by the action of protons on the wall.