Energetics of Active Transport Processes

Discussions of active transport usually assume stoichiometry between the rate of transport J₊ and the metabolic rate J_r. However, the observation of a linear relationship between J₊ and J_r does not imply a stoichiometric relationship, i.e., complete coupling. Since coupling may possibly be incomplete, we examine systems of an arbitrary degree of coupling q, regarding stoichiometry as a limiting case. We consider a sodium pump, with J₊ and J_r linear functions of the electrochemical potential difference, -X₊, and the chemical affinity of the metabolic driving reaction, A. The affinity is well defined even for various complex reaction pathways. Incorporation of a series barrier and a parallel leak does not affect the linearity of the composite observable system. The affinity of some region of the metabolic chain may be maintained constant, either by large pools of reactants or by regulation. If so, this affinity can be evaluated by two independent methods. Sodium transport is conveniently characterized by the open-circuit potential (Δψ)_I=0 and the natural limits, level flow (J₊)_X+=0, and static head X⁰₊ = (X₊)_J+=0. With high degrees of coupling -X⁰₊/F approaches the electromotive force E_Na (Ussing); -X⁰₊/F cannot be identified with ((RT/F) ln f)_X+=0, where f is the flux ratio. The efficiency η = -J₊X₊/J_rA is of significance only when appreciable energy is being converted from one form to another. When either J₊ or -X₊ is small η is low; the significant parameters are then the efficacies ε_J+ = J₊/J_rA and ε_X+ = -X₊/J_rA, respectively maximal at level flow and static head. Leak increases both J₊ and ε_J+ for isotonic saline reabsorption, but diminishes -X⁰₊ and ε_X♀. Electrical resistance reflects both passive parameters and metabolism. Various fundamental relations are preserved despite coupling of passive ion and water flows.     

Analytical studies of rapidly inactivating and noninactivating sodium currents in differentiated NG108-15 neuronal cells

The rapidly inactivating (I_Naf) and noninactivating Na⁺ currents (I_Na(NI)) were characterized in NG108-15 neuronal cells differentiated with dibutyryl cyclic AMP in this study. Standard activation and inactivation protocols were used to evaluate the steady-state and kinetic properties of the I_Naf present in these cells. The voltage protocols with a slowly depolarizing ramp were implemented to examine the properties of I_Na(NI). Based on experimental data and computer simulations, a window component of the rapidly inactivating sodium current (I_Naf(W)) was also generated in response to the slowly depolarizing ramp. The I_Naf(W) was subtracted from I_Na(NI) to yield the persistent Na⁺ current (I_Na(P)). Our results demonstrate the presence of I_Na(P) in these cells. In addition to modifying the steady-state inactivation of I_Naf, ranolazine or riluzloe could be effective in blocking I_Naf(W) and I_Na(P). The ability of ranolazine and riluzole to suppress I_Na(P) was greater than their ability to inhibit I_Naf(W). In current-clamp recordings, current-induced voltage oscillations were applied to elicit action potentials (APs) through a gradual transition between spontaneous depolarization and upstroke. Ranolazine or riluzole at a concentration of 3 μM then effectively suppressed the AP firing generated by oscillatory changes in membrane current. The data suggest that a small rise in I_Na(NI) facilitates neuronal hyper-excitability due the decreased threshold of AP initiation. The underlying mechanism of the inhibitory actions of ranolazine or riluzole on membrane potential in neurons or neuroendocrine cells in vivo may thus be associated with their blocking of I_Na(NI).     

Variations in Temperature Sensitivity (Q10) of CH4 Emission from a Subtropical Estuarine Marsh in Southeast China

Understanding the functional relationship between greenhouse gas fluxes and environmental variables is crucial for predicting the impacts of wetlands on future climate change in response to various perturbations. We examined the relationships between methane (CH₄) emission and temperature in two marsh stands dominated by the Phragmites australis and Cyperus malaccensis, respectively, in a subtropical estuarine wetland in southeast China based on three years of measurement data (2007–2009). We found that the Q₁₀ coefficient of CH₄ emission to soil temperature (Q_s10) from the two marsh stands varied slightly over the three years (P > 0.05), with a mean value of 3.38 ± 0.46 and 3.89 ± 0.41 for the P. australis and C. malaccensis stands, respectively. On the other hand, the three-year mean Q_a10 values (Q₁₀ coefficients of CH₄ emission to air temperature) were 3.39 ± 0.59 and 4.68 ± 1.10 for the P. australis and C. malaccensis stands, respectively, with a significantly higher Q_a10 value for the C. malaccensis stand in 2008 (P < 0.05). The seasonal variations of Q₁₀ (Q_s10 and Q_a10) differed among years, with generally higher values in the cold months than those in the warm months in 2007 and 2009. We found that the Q_s10 values of both stands were negatively correlated with soil conductivity, but did not obtain any conclusive results about the difference in Q₁₀ of CH₄ emission between the two tidal stages (before flooding and after ebbing). There were no significant differences in both Q_s10 and Q_a10 values of CH₄ emission between the P. australis stand and the C. malaccensis stands (P > 0.05). Our results show that the Q₁₀ values of CH₄ emission in this estuarine marsh are highly variable across space and time. Given that the overall CH₄ flux is governed by a suite of environmental factors, the Q₁₀ values derived from field measurements should only be considered as a semi-empirical parameter for simulating CH₄ emissions.     

Diffusion and sedimentation interaction parameters for measuring the second virial coefficient and their utility as predictors of protein aggregation

The concentration-dependence of the diffusion and sedimentation coefficients (k_D and k_s, respectively) of a protein can be used to determine the second virial coefficient (B₂), a parameter valuable in predicting protein-protein interactions. Accurate measurement of B₂ under physiologically and pharmaceutically relevant conditions, however, requires independent measurement of k_D and k_s via orthogonal techniques. We demonstrate this by utilizing sedimentation velocity (SV) and dynamic light scattering (DLS) to analyze solutions of hen-egg white lysozyme (HEWL) and a monoclonal antibody (mAb1) in different salt solutions. The accuracy of the SV-DLS method was established by comparing measured and literature B₂ values for HEWL. In contrast to the assumptions necessary for determining k_D and k_s via SV alone, k_D and ks were of comparable magnitudes, and solution conditions were noted for both HEWL and mAb1 under which 1), k_D and k_s assumed opposite signs; and 2), k_D ≥ k_s. Further, we demonstrate the utility of k_D and k_s as qualitative predictors of protein aggregation through agitation and accelerated stability studies. Aggregation of mAb1 correlated well with B₂, k_D, and k_s, thus establishing the potential for k_D to serve as a high-throughput predictor of protein aggregation.     

Dual recognition of S 1 and S 4 pistils by S 4 sm pollen in self-incompatibility of Japanese pear (Pyrus pyrifolia Nakai)

Most cultivars of Japanese pear (Pyrus pyrifolia Nakai) exhibit gametophytic self-incompatibility controlled by a single S-locus with multiple S-haplotypes. A self-compatible (SC) cultivar, ??Osanijisseiki?? (S ₂ S ₄ ^sm ), arising by a bud mutation of ??Nijisseiki?? (S ₂ S ₄ ), has a stylar-part mutant S ₄ ^sm -haplotype, which lacks the pistil S ₄ gene, which is the S ₄ -RNase gene. To efficiently breed SC cultivars, we selected ??Nashi Chuukanbohon Nou 1 Gou?? (??NCN1??) harboring homozygous S ₄ ^sm from a self-progeny of Osanijisseiki and crossed it with ??Okusankichi?? (S ₅ S ₇ ), ??Hakkou?? (S ₄ S ₅ ), or ??Ri-14?? (S ₁ S ₂ ). Fruit set (%) was compared after self-pollination of the trees in the three progenies. All trees derived from the three progenies were predicted to be SC, except for the S ₄ S ₄ ^sm trees in the progeny of NCN1 × Hakkou. However, S ₁ S ₄ ^sm trees in the progeny of NCN1 × Ri-14 proved to be self-incompatible (SI). The pollen from Osanijisseiki was incompatible with ??Doitsu?? (S ₁ S ₂ ), but that from Nijisseiki was compatible, suggesting a possibility that the S ₄ ^sm pollen was rejected by S ₁ -harboring pistils. This possibility was clarified by crossing the pollen from NCN1 (S ₄ ^sm S ₄ ^sm ) to Doitsu, ??Imamuraaki?? (S ₁ S ₆ ), or ??Hougetsu?? (S ₁ S ₇ ), all of which proved incompatible. On the other hand, S ₄ ^sm pollen was accepted by pistils harboring the S ₂ , S ₃ , S ₅ , S ₆ , S ₇ , S ₉ , and S _k haplotypes. The dual recognition of S ₁ and S ₄ pistils by S ₄ ^sm pollen can be attributed to a mutation of the pollen S ₄ gene(s).     

The redox potentials of the b-type cytochromes of higher plant chloroplasts

1. In fresh chloroplasts, three b-type cytochromes exist. These are b-559_HP (λ_max, 559 nm; E_m at pH 7, +370 mV; pH-independent E_m), b-559_LP (λ_max, 559 nm; E_m at pH 7, +20 mV; pH-independent E_m) and b-563 (λ_max, 563 nm; E_m at pH 7, ?110 mV; pH-independent E_m). b-559_HP may be converted to a lower potential form (λ_max, 559 nm; E_m at pH 7, +110 mV; pH-independent E_m).2. In catalytically active b-f particle preparations, three cytochromes exist. These are cytochrome f (λ_max, 554 nm; E_m at pH 7, +375 mV, pK on oxidised cytochrome at pH 9), b-563 (λ_max, 563 nm; E_m at pH 7, ?90 mV, small pH-dependence of E_m) and a b-559 species (λ_max, 559 nm, E_m at pH 7, +85 mV; pH-independent E_m).3. A positive method of demonstration and estimation of b-559_LP in fresh chloroplasts is described which involves the use of menadiol as a selective reductant of b-559_LP.     

The roles of Rhodobacter sphaeroides copper chaperones PCuAC and Sco (PrrC) in the assembly of the copper centers of the aa3-type and the cbb3-type cytochrome c oxidases

The α proteobacter Rhodobacter sphaeroides accumulates two cytochrome c oxidases (CcO) in its cytoplasmic membrane during aerobic growth: a mitochondrial-like aa₃-type CcO containing a di-copper Cu_A center and mono-copper Cu_B, plus a cbb₃-type CcO that contains Cu_B but lacks Cu_A. Three copper chaperones are located in the periplasm of R. sphaeroides, PCu_AC, PrrC (Sco) and Cox11. Cox11 is required to assemble Cu_B of the aa₃-type but not the cbb₃-type CcO. PrrC is homologous to mitochondrial Sco1; Sco proteins are implicated in Cu_A assembly in mitochondria and bacteria, and with Cu_B assembly of the cbb₃-type CcO. PCu_AC is present in many bacteria, but not mitochondria. PCu_AC of Thermus thermophilus metallates a Cu_A center in vitro, but its in vivo function has not been explored. Here, the extent of copper center assembly in the aa₃- and cbb₃-type CcOs of R. sphaeroides has been examined in strains lacking PCu_AC, PrrC, or both. The absence of either chaperone strongly lowers the accumulation of both CcOs in the cells grown in low concentrations of Cu^2 +. The absence of PrrC has a greater effect than the absence of PCu_AC and PCu_AC appears to function upstream of PrrC. Analysis of purified aa₃-type CcO shows that PrrC has a greater effect on the assembly of its Cu_A than does PCu_AC, and both chaperones have a lesser but significant effect on the assembly of its Cu_B even though Cox11 is present. Scenarios for the cellular roles of PCu_AC and PrrC are considered. The results are most consistent with a role for PrrC in the capture and delivery of copper to Cu_A of the aa₃-type CcO and to Cu_B of the cbb₃-type CcO, while the predominant role of PCu_AC may be to capture and deliver copper to PrrC and Cox11. This article is part of a Special Issue entitled: Biogenesis/Assembly of Respiratory Enzyme Complexes.     

The effect of pyramiding Phytophthora infestans resistance genes R Pi-mcd1 and R Pi-ber in potato

Despite efforts to control late blight in potatoes by introducing R _pi -genes from wild species into cultivated potato, there are still concerns regarding the durability and level of resistance. Pyramiding R _pi -genes can be a solution to increase both durability and level of resistance. In this study, two resistance genes, R _Pi-mcd1 and R _Pi-ber , introgressed from the wild tuber-bearing potato species Solanum microdontum and S. berthaultii were combined in a diploid S. tuberosum population. Individual genotypes from this population were classified after four groups, carrying no R _pi -gene, with only R _Pi-mcd1 , with only R _Pi-ber , and a group with the pyramided R _Pi-mcd1 and R _Pi-ber by means of tightly linked molecular markers. The levels of resistance between the groups were compared in a field experiment in 2007. The group with R _Pi-mcd1 showed a significant delay to reach 50% infection of the leaf area of 3 days. The group with R _Pi-ber showed a delay of 3 weeks. The resistance level in the pyramid group suggested an additive effect of R _Pi-mcd1 with R _Pi-ber . This suggests that potato breeding can benefit from combining individual R _pi -genes, irrespective of the weak effect of R _Pi-mcd1 or the strong effect of R _Pi-ber .     

Theoretical series elastic element length in Rana pipiens sartorius muscles

Assuming a two component system for the muscle, a series elastic element and a contractile component, the analyses of the isotonic and isometric data points were related to obtain the series elastic stiffness, dP/dl_s, from the relation, See PDF for Equation From the isometric data, dP/dt was obtained and shortening velocity, v, was a result of the isotonic experiments. Substituting (P₀ - P)/T for dP/dt and (P₀ - P)/(P + a) times b for v, dP/dl_s = (P + a) /bT, where P < P₀, and a, b are constants for any lengths l ≤ l₀ (Matsumoto, 1965). If the isometric tension and the shortening velocity are recorded for a given muscle length, l₀, although the series elastic, l_s, and the contractile component, l_c, are changing, the total muscle length, l₀ remains fixed and therefore the time constant, T. Integrating, See PDF for Equation the stress-strain relation for the series elastic element, See PDF for Equation is obtained; l_sc0 - l_s + l_c0where l_co equals the contractile component length for a muscle exerting a tension of P₀. For a given P/P₀, l_s is uniquely determined and must be the same whether on the isotonic or isometric length-tension-time curve. In fact, a locus on one surface curve can be associated with the corresponding locus on the other.     

The structural dependence of amino acid hydrophobicity parameters

Amino acid hydrophobicity parameters, G_hp log P (partition coefficient) values, free energies of solution, G_sol and hydration numbers, are well correlated by equations derived from the relationship O_X = Aα_X + Lσ_IX + Sν_X + I_iX + H₁n_HX + H₂n_nX + b₀ where O is the quantity correlated; X denotes the amino acid side chain; α is a polarizability parameter; σ_I, a localized electrical effect parameter; ν, a steric parameter; i, an indicator variable which accounts for an ionic X ; n_H and n_n the number of OH or NH bonds and of full nonbonding orbitals in X, respectively, and b₀ is the intercept. The equation is based on the assumption that Δ_hp log P and ΔG_sol are all functions of the difference in intermolecular forces between the amino acid and some medium, and the amino acid and water. The parameters were chosen to model the intermolecular forces of interest.Generally the most important factor is α_x. This is followed by ν, i, and n_H. Least important is σ_I. ΔG_sol depends on α, n_H and n_n. Hydration numbers depend on i, n_H and n_n. The hydrophobicity of amino acid side chains is the result of a preference for a nonpolar medium as a increases and for a polar medium as i, n_H and σ_I increase. It is quantitatively accounted for by the model, and no special “hydrophobic bond” need be involved. The results show that log P values for amino acids are composite quantities whose composition is variable.     

Analysis of genes controlling f(1) sterility in rice by the use of isogenic lines

In order to look into the genetic basis of intervarietal F₁ sterility in rice (Oryza sativa L.), a series of backcrosses (up to B₁₃) was carried out using Taichung 65 (Japonica type) as the recurrent parent and several Indica varieties as donor parents. A number of "isogenic F₁-sterile lines" were isolated by test-crossing fertile F₂ plants obtained from the selfing of partly pollensterile backcross segregants. Crossing experiments with the isogenic lines confirmed the author's previous hypothesis that there are sets of duplicate gametic lethals (s genes) and that gametes carrying a double recessive combination (s₁s₂) of these deteriorate during development, though in the present hypothesis the genes are considered to affect the development of microspores only. Assuming that Taichung 65 has the genotype s₁/s₁ + ₂/+₂ and a donor parent (like an isogenic F₁-sterile line derived from it) has +₁/+₁s₂/s₂, pollen grains with +₁s₂ have shown a higher fertilizing capacity in the genetic background of Taichung 65 than those with s₁ +₂, while those with +₁ +₂ have a lower fertilizing capacity. This certational advantage of alien genes was considered to be an internal mechanism that helped the development of F₁ sterility relationships among rice varieties. The isogenic F₁-sterile lines derived from different donor parents each had a set of s genes at different loci. Linkage relations were detected between the s loci and three gene markers.     

Clothing insulation and temperature,layer and mass of clothing under comfortable environmental conditions

This study was designed to investigate the relationship between the microclimate temperature and clothing insulation (I_cl) under comfortable environmental conditions. In total, 20 subjects (13 women, 7 men) took part in this study. Four environmental temperatures were chosen: 14°C (to represent March/April), 25°C (May/June), 29°C (July/August), and 23°C (September/October). Wind speed (0.14ms^-1) and humidity (45%) were held constant. Clothing microclimate temperatures were measured at the chest (T_chest) and on the interscapular region (T_scapular). Clothing temperature of the innermost layer (T_innermost) was measured on this layer 30 mm above the centre of the left breast. Subjects were free to choose the clothing that offered them thermal comfort under each environmental condition. We found the following results. 1) All clothing factors except the number of lower clothing layers (L_lower), showed differences between the different environmental conditions (P<0.05). The ranges of T_chest were 31.6 to 33.5°C and 32.2 to 33.4°C in T_scapular. The range of T_innermost was 28.6 to 32.0°C. The range of the upper clothing layers (L_upper) and total clothing mass (M_total) was 1.1 to 3.2 layers and 473 to 1659 g respectively. The range of I_cl was 0.78 to 2.10 clo. 2) Post hoc analyses showed that analysis of T_innermost produced the same results as for that of I_cl. Likewise, the analysis of L_upper produced the same result as the analysis of the number of total layers (L_total) within an outfit. 3) Air temperature (t_a) had positive relationships with T_chest and T_scapular and with T_innermost but had inverse correlations with I_cl, M_total, L_upper and L_total. T_chest, T_scapular, and T_innermost increased as t_a rose. 4) I_cl had inverse relationships with T_chest and T_innermost, but positive relationships with M_total, L_upper and L_total. I_cl could be estimated by M_total, L_upper, and T_scapular using a multivariate linear regression model. 5) L_upper had positive relationships with I_cl and M_total, but L_lower did not. Subjects hardly changed L_lower under environmental comfort conditions between March and October. This indicates that each of the T_chest, M_total, and L_upper was a factor in predicting I_cl. T_innermost might also be a more influential factor than the clothing microclimate temperature.     

Prediction of mean skin temperature for use as a heat strain scale by introducing an equation for sweating efficiency

The present paper made the heat balance equation (HBE) for nude or minimally clad subjects a linear function of mean skin temperature (t _sk) by applying new equations for sweating efficiency (η _sw) and thermoregulatory sweat rate (S _wR). As the solution of the HBE, the equation predicting t _sk was derived and used for a heat strain scale of subjects. The η _sw was proportional to the reciprocal of S _w/E _max (S _w, sweat rate; E _max maximum evaporative capacity) and the S _wR was proportional to t _sk with a parameter of the sweating capacity of the subject. The errors of predicted t _sk from observations due to the approximation of η _sw were examined based on experimental data conducted on eight young male subjects. The value of errors of t _sk was ?0.10?±?0.42 °C (mean?±?sample standard deviation (SSD)). We aim to apply the predicted t _sk of a subject at a level of sweating capacity as a heat strain scale of a function of four environmental factors (dry- and wet-bulb temperatures, radiation, and air velocity) and three human factors (metabolic rate, sweating capacity, and clothing (≤0.2clo)).     

Rotor architecture in the yeast and bovine F1-c-ring complexes of F-ATP synthase

The F₁F_O-ATP synthase is a rotary molecular nanomotor. F₁ is a chemical motor driven by ATP hydrolysis while F_O is an electrical motor driven by the proton flow. The two stepping motors are mechanically coupled through a common rotary shaft. Up to now, the three available crystal structures of the F₁c₁₀ sub-complex of the yeast F₁F_O-ATP synthase were isomorphous and then named yF₁c₁₀(I). In this crystal form, significant interactions of the c₁₀-ring with the F₁-head of neighboring molecules affected the overall conformation of the F₁-c-ring complex. The symmetry axis of the F₁-head and the inertia axis of the c-ring were tilted near the interface between the F₁-central stalk and the c-ring rotor, resulting in an unbalanced machine. We have solved a new crystal form of the F₁c₁₀ complex, named yF₁c₁₀(II), inhibited by adenylyl-imidodiphosphate (AMP-PNP) and dicyclohexylcarbodiimide (DCCD), at 6.5 Å resolution in which the crystal packing has a weaker influence over the conformation of the F₁-c-ring complex. yF₁c₁₀(II) provides a model of a more efficient generator. yF₁c₁₀(II) and bovine bF₁c₈ structures share a common rotor architecture with the inertia center of the F₁-stator close to the rotor axis.     

Phosphate transport in rat liver mitochondria--a mobile carrier model.

The possibility of a mobile carrier model for phosphate transport in rat liver mitochondria was examined on the basis of counterflux experiments. The rate of P_i uptake and P_i exchange were identical and depended on the external pH value. The alkalization of the suspending medium of P_i-preloaded mitochondria induced an efflux of P_i. The induction of a net P_i efflux by alkalization of the external medium stimulated the rate of ³²P_i uptake. Arsenate was shown to be an alternative substrate for P_i-carrier. A net efflux of inorganic arsenate (As_i), induced by alkalization of the external medium, also supported an acceleration of the ³²P_i uptake. When mitochondria were first preloaded with As_i and ³²P_i and then diluted into a more alkaline buffer free of Asi, a transient uptake of ³²P_i was observed. These results are discussed in terms of reorientation of the active site of the P_i carrier under the conditions where a net efflux of P_i or As_i occurred. This conclusion was supported by a change in the accessibility of the SH groups of the carrier toward poorly permeant thiol reagents during that process.     

Patterns of Sequence Divergence and Evolution of the S1 Orthologous Regions between Asian and African Cultivated Rice Species

A strong postzygotic reproductive barrier separates the recently diverged Asian and African cultivated rice species, Oryza sativa and O. glaberrima. Recently a model of genetic incompatibilities between three adjacent loci: S₁A, S₁ and S₁B (called together the S₁ regions) interacting epistatically, was postulated to cause the allelic elimination of female gametes in interspecific hybrids. Two candidate factors for the S₁ locus (including a putative F-box gene) were proposed, but candidates for S₁A and S₁B remained undetermined. Here, to better understand the basis of the evolution of regions involved in reproductive isolation, we studied the genic and structural changes accumulated in the S₁ regions between orthologous sequences. First, we established an 813 kb genomic sequence in O. glaberrima, covering completely the S₁A, S₁ and the majority of the S₁B regions, and compared it with the orthologous regions of O. sativa. An overall strong structural conservation was observed, with the exception of three isolated regions of disturbed collinearity: (1) a local invasion of transposable elements around a putative F-box gene within S₁, (2) the multiple duplication and subsequent divergence of the same F-box gene within S₁A, (3) an interspecific chromosomal inversion in S₁B, which restricts recombination in our O. sativa×O. glaberrima crosses. Beside these few structural variations, a uniform conservative pattern of coding sequence divergence was found all along the S₁ regions. Hence, the S₁ regions have undergone no drastic variation in their recent divergence and evolution between O. sativa and O. glaberrima, suggesting that a small accumulation of genic changes, following a Bateson-Dobzhansky-Muller (BDM) model, might be involved in the establishment of the sterility barrier. In this context, genetic incompatibilities involving the duplicated F-box genes as putative candidates, and a possible strengthening step involving the chromosomal inversion might participate to the reproductive barrier between Asian and African rice species.     

Comparative growth analyses of panicum species with differing rates of photorespiration

Panicum milioides, a naturally occurring species with reduced photorespiration, P. bisulcatum, a C₃ species, and P. miliaceum, a C₄ species, were grown for 4 weeks at altered pO₂ and pCO₂ and several vegetative growth parameters were determined at weekly intervals. Compared to a pO₂ of 10%, a greater O₂ inhibition of the relative growth rate and dry matter production was observed for P. bisulcatum than for P. milioides at both 21% and 40% O₂, whereas little effect of O₂ was noted for P. miliaceum. Similarly, exposures to elevated pCO₂ of 500 and 1000 μ1 CO₂/liter resulted in a greater stimulation of vegetative growth for P. bisulcatum than for P. milioides, with little effect on P. miliaceum. The CO₂ compensation concentration of P. milioides was less than that of P. bisulcatum over a pO₂ range of 5 to 40%. At 5% O₂, the compensation concentration was relatively O₂-insensitive, whereas above 5% it increased with increasing pO₂. It is concluded that P. milioides represents the first well documented example of a C₃ plant with reduced photorespiration, based on both leaf CO₂ exchange parameters and growth analyses of dry matter production.     

Mixed and uniform co-operativity of ligand binding to multisite proteins: the co-operativity types allowed by the adair equation and conditions for them

It is proved for the first time that the macroscopic co-operativity of binding to a protein with q binding sites may change signs over a single binding curve any number of times from 0 to (q-2), but no more than (q-2). n changes of sign of macroscopic co-operativity requires as a necessary condition at least n changes of sign of microscopic co-operativity, but this necessary condition is not a sufficient one. The necessary and sufficient condition that decides whether there are two changes of sign in a four-site protein is obtained. There are no changes when K₁K₃(K₂-K₄)+K₁K₂(K₃-K₂)+K₂K₃(K₄-K₃) is positive, and two changes when it is negative, presuming the above mentioned necessary conditions to be satisfied. The K's of this formula are the “intrinsic” per-site Adair constants. As a result, the conditions for all six co-operativity types possible with a four-site protein are now known.     

Molecular packing and intermolecular contacts of sickling deer type III hemoglobin

The X-ray structure of sickling deer type III hemoglobin, solved by the molecular replacement method and refined to an R value of ~25%, has been used to determine the mode of molecular packing and the residues involved in the intermolecular contacts between the hemoglobin tetramers in the crystalline state. The molecules pack in linear arrays (“fibrils”), with adjacent fibrils displaced ~27 Å from one another along the long axis of the arrays. A view down this axis shows an hexagonal network of six fibrils surrounding a central solvent cavity (each hexameric unit is termed a fiber) with adjacent fibers sharing a common wall of fibrils. Contacts less than 5 Å are observed between the following subunits of different molecules: α₁α′₁, α₁α′₂, α₁β′₁, α₁β′₂, α₂β′₁, α₂β′₂, β₂β′₂, in which the primes refer to adjacent molecules.