The amino acid sequence of peanut agglutinin

The amino acid sequence of peanut (Arachis hypogaea) agglutinin was determined from three major fragments obtained by mild acid cleavage at Asp-Pro peptide bonds. The sequence of 236 amino acids has residues identical to those that form the metal-binding site and the hydrophobic pocket in concanavalin A and other lectins, although the overall similarity is only 42%. In the segments of peanut agglutinin that correspond to the four loops that form the carbohydrate-binding site in concanavalin A and favin, several central residues are homologous, while others show changes to smaller side chains, such as Tyr----Gly. The carbohydrate-binding site of peanut agglutinin may therefore have a similar peptide-backbone architecture, but form a considerably more open cleft.     

Alterations in Cortical [3H]Kainate and α-[3H]Amino-3-Hydroxy-5-Methyl-4-Isoxazolepropionic Acid Binding in a Spontaneous Canine Model of Chronic Hepatic Encephalopathy

Excitatory amino acid receptor binding parameters were investigated in a spontaneous dog model of chronic hepatic encephalopathy. L-[3H]Glutamate, (+)-[3H]-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-im ine maleate ([3H]MK-801), [3H]kainate, and alpha-[3H]-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid ([3H]AMPA) binding experiments were performed using crude cerebrocortical synaptosomal membrane preparations from dogs with congenital portosystemic encephalopathy (PSE) and control dogs. There was no change in the affinity or density of L-[3H]-glutamate or [3H]MK-801 binding sites in dogs with congenital PSE compared with control dogs. However, in the PSE dogs there was a significant reduction in the density of [3H]kainate binding sites compared with control dogs and abolition of the low-affinity [3H]AMPA binding site. The relative binding capacity of PSE synaptosomal membranes for [3H]kainate and [3H]AMPA was expressed as the ratio Bmax/KD. There was a significant inverse correlation between the Bmax/KD ratio for [3H]AMPA binding and the worst grade of encephalopathy experienced by each dog. These results suggest that there is a significant perturbation of cerebrocortical non-N-methyl-D-aspartate receptor binding in dogs with congenital PSE which may have relevance to the pathogenesis of hepatic encephalopathy.     

Socially stimulated androgen surges in male hamsters: the roles of vaginal secretions, behavioral interactions, and housing conditions.

The sources of cues necessary for elicitation of androgen surges and sexual behavior in male golden hamsters (Mesocricetus auratus) were investigated. Circulating androgen levels were measured in males after interactions with other males or several types of estrous females: intact females, vaginectomized females, or vaginectomized females scented with vaginal secretions. All groups of males that interacted with estrous females demonstrated significant elevations in androgens whereas those that interacted with other males did not. Thus, the presence of vaginal secretions is not necessary for the elicitation of androgen surges in sexually experienced male hamsters. Individual differences in sexual performance were not correlated with the degree of change in androgen levels, suggesting that such hormonal responses are not graded but are all-or-none. Housing males in isolation from females did not alter either baseline androgen levels or the magnitude of androgen responses caused by interactions with females.     

Selective inhibition of mutant Ha-ras mRNA expression by antisense oligonucleotides.

A biological reporter gene assay was employed to determine the crucial parameters for maximizing selective targeting of a Ha-ras codon 12 point mutation (G----T) using phosphorothioate antisense oligonucleotides. We have tested a series of oligonucleotides ranging in length between 5 and 25 bases, each centered around the codon 12 point mutation. Our results indicate that selective targeting of this point mutation can be achieved with phosphorothioate antisense oligonucleotides, but this selectivity is critically dependent upon oligonucleotide length and concentration. The maximum selectivity observed in antisense experiments, 5-fold for a 17-base oligonucleotide, was closely predicted by a simple thermodynamic model that relates the fraction of mutant to wild type target bound as a function of oligonucleotide concentration and affinity. These results suggest thermodynamic analysis of oligonucleotide/target interactions is useful in predicting the specificity that can be achieved by an antisense oligonucleotide targeted to a single base point mutation.     

The acquisition of inorganic carbon by four red macroalgae

Photosynthesis was studied in four species of red marine macroalgae: Palmaria palmata, Laurencia pinnatifida, Lomentaria articulata and Delesseria sanguinea. The rate of O₂ evolution for submersed photosynthesis was measured as a function of incident photon flux density at normal pH and inorganic carbon concentration (pH 8.0, 2 mol m^–3), and as a function of inorganic carbon concentration at pH 8.0 at saturating and at limiting photon flux density. The rate of CO₂ uptake was measured for emersed photosynthesis as a function of CO₂ partial pressure at saturating photon flux density. Previous pH-drift results suggest that Palmaria and Laurencia are able to use HCO _inf3 ^sup– as well as CO₂ whereas Lomentaria and Delesseria are restricted to CO₂. None of the algae are saturated by 2 mol m^–3 inorganic carbon at high light (400 mol m^–2 s^–1) but are saturated at low light (35 mol m^–2 s^–1). The inorganic C concentration at which half the light-saturated rate of O₂ evolution is achieved is higher for Palmaria and Laurencia (1.51 and 1.85 mol m^–3) than for Lomentaria and Delesseria (0.772 and 0.841 mol m^–3). The lower values for the latter two species could reflect their putative restriction to CO₂. If expressed in terms of CO₂, the half-saturation values yield 7.2 and 7.8 mmol m^–3 respectively, which are very similar to values obtained previously during pH-drift experiments but at lower concentrations of HCO _inf3 ^sup– , consistent with restriction to CO₂. The photosynthetic conductance (m s^–1), calculated from the initial slope for photosynthesis at low concentrations of inorganic carbon, correlates with the suggested ability to extract inorganic carbon based on pH-drift results. Calculations made assuming that CO₂ is the only species diffusing across the boundary layer are consistent with boundary layer thicknesses of 20 and 19 m for Lomentaria and Delesseria respectively, which is feasible given the rapid water movement in the experiments. For Laurencia however, an unreasonably small boundary layer thickness of 6 m is necessary to explain the flux, which indicates co-diffusion by HCO _inf3 ^sup– . In the apparent absence of external carbonic anhydrase, direct uptake of HCO _inf3 ^sup– , rather than external conversion to CO₂ is indicated in this species. In air, the CO₂ concentration at which photosynthesis is half-maximal increases in the same order as the ability to raise pH in drift experiments. At 21 kPa the CO₂ compensation partial pressures for Palmaria and Laurencia at 0.56 and 1.3 Pa are low enough to suggest a carbon-concentrating mechanism is operating, while those of Lomentaria at 1.8 Pa and particularly that of Delesseria at 4.5 Pa could be explained without a carbon-concentrating mechanism. The algae tested (all except Delesseria) showed more O₂ evolution than could be accounted for with a photosynthetic quotient of 1.0 and uncatalysed conversion of HCO _inf3 ^sup– to CO₂ outside the cell in high light at pH 8.0 when high algal fresh weight per unit medium was used. These results are concordant with other data suggesting use of HCO _inf3 ^sup– by Palmaria and Laurencia, but discordant with the rest of the available information in indicating use of HCO _inf3 ^sup– by Lomentaria. The reason for this is unclear. The lightsaturated rate of O₂ evolution on an algal area basis and the photon flux density needed to saturate photosynthesis were related partly to the habitat from which the seaweeds were collected, but more strongly to the ability to use HCO _inf3 ^sup– . Values for the two users of HCO _inf3 ^sup– , Palmaria (population used was intertidal; also occurs subtidally) and Laurencia (intertidal/shaded intertidal), were greater than for Lomentaria (shaded intertidal), which was greater than Delesseria (subtidal), both of which are believed to be restricted to CO₂. In accordance with earlier ¹³C data and, for Delesseria, estimates of the achieved growth rates in situ, carbon is likely to be saturating and use of HCO _inf3 ^sup– is unlikely to occur in the normal low-light habitats of Lomentaria and Delesseria. Analysis of N-use efficiencies show that they are closer to the low-CO₂-affinity Laminariales than the high-CO₂-affinity Fucaceae.     

Discrimination between12C and13C by marine plants

Summary The natural abundance¹³C/¹²C ratios (as δ¹³C) of organic matter of marine macroalgae from Fife and Angus (East Scotland) were measured for comparison with the species' ability to use CO₂ and HCO ₃ ^- for photosynthesis, as deduced from previously published pH-drift measurements. There was a clear difference in δ¹³C values for species able or unable to use HCO ₃ ^- . Six species of Chlorophyta, 12 species of Phaeophyta and 8 species of Rhodophyta that the pH-drift data suggested could use HCO ₃ ^- had δ¹³C values in the range -8.81‰ to -22.55‰. A further 6 species of Rhodophyta which the pH-drift data suggested could only use CO₂ had δ¹³C values in the range -29.90‰ to-34.51‰. One of these six species (Lomentaria articulata) is intertidal; the other five are subtidal and so have no access to atmospheric CO₂ to complicate the analysis. For these species, calculations based on the measured δ¹³C of the algae, the δ¹³C of CO₂ in seawater, and the known¹³C/¹²C discrimination of CO₂ diffusion and RUBISCO carboxylation suggest that only 15–21% of the limitation to photosynthesisin situ results from CO₂ diffusion from the bulk medium to the plastids; the remaining 79–85% is associated with carboxylation reactions (and, via feedback effects, down-stream processes). This analysis has been extended for one of these five species,Delesseria sanguinea, by incorporating data onin situ specific growth rates, respiratory rates measured in the laboratory, and applying Fick's law of diffusion to calculate a boundary layer thickness of 17–24 μm. This value is reasonable for aDelesseria sanguinea frondin situ. For HCO ₃ ^- -using marine macroalgae the range of δ¹³C values measured can be accommodated by a CO₂ efflux from algal cells which range from 0.306 of the gross HCO ₃ ^- influx forEnteromorpha intestinalis (δ¹³C=-8.81‰) in a rockpool to 0.787 forChondrus crispus (δ¹³C=-22.55‰). The relatively high computed CO₂ efflux for those HCO ₃ ^- -users with the more negative δ¹³C values implies a relatively high photon cost of C assimilation; the observed photon costs can be accommodated by assuming coupled, energy-independent inorganic carbon influx and efflux. The observed δ¹³C values are also interpreted in terms of water movement regimes and obtaining CO₂ from the atmosphere. Published δ¹³C values for freshwater macrophytes were compared with the ability of the species to use CO₂ and HCO ₃ ^- and again there was an apparent separation in δ¹³C values for these two groups. δ¹³C values obtained for marine macroalgae for which no pH-drift data are available permit predictions, as yet untested, as to whether they use predominantly CO₂ or HCO ₃ ^-     

Radiation-induced micrencephaly in guinea pigs.

The effect of X rays on brain weight of guinea pig pups at birth was studied in 21-day-old embryos exposed in utero to doses of 75 and 100 mGy. When compared to controls and when corrected for body weight, gestation time, litter size, sex, and examiner differences, the brains of irradiated pups weighed approximately 46 mg less than those of controls (P < 0.001) for the 75-mGy group and about 55 mg less for the 100-mGy group. Brains of females weighed 51 mg less than those of males of the same body weight. Dam weight and caging conditions had no observed effect on brain weight.     

The small GTP-binding protein rac regulates growth factor-induced membrane ruffling.

The function of rac, a ras-related GTP-binding protein, was investigated in fibroblasts by microinjection. In confluent serum-starved Swiss 3T3 cells, rac1 rapidly stimulated actin filament accumulation at the plasma membrane, forming membrane ruffles. Several growth factors and activated H-ras also induced membrane ruffling, and this response was prevented by a dominant inhibitory mutant rac protein, N17rac1. This suggests that endogenous rac proteins are required for growth factor-induced membrane ruffling. In addition to membrane ruffling, a later response to both rac1 microinjection and some growth factors was the formation of actin stress fibers, a process requiring endogenous rho proteins. Using N17rac1 we have shown that these growth factors act through rac to stimulate this rho-dependent response. We propose that rac and rho are essential components of signal transduction pathways linking growth factors to the organization of polymerized actin.     

Solvent effects on biocatalysis in organic systems: equilibrium position and rates of lipase catalyzed esterification

Porcine pancreatic lipase immobilized on celite particles has been employed as a catalyst for the esterification of dodecanol and decanoic acid in a predominantly organic system. Solvent influence on the equilibrium position and on the catalyst activity has been studied using 20 solvents, including aliphatic and aromatic hydrocarbons, ethers, ketones, nitro- and halogenated hydrocarbons, and esters. The equilibrium constant for esterification correlates well with the solubility of water in the organic solvent, which in turn shows a good relationship with a function of Guttman's donor number and the electron pair acceptance index number of the solvent. This may be rationalized in terms of the requirements for solvation of water and of the reactants. The catalyst activity, measured as the initial rate of the esterification reaction, is best correlated as a function of both n-octanol-water partition coefficient (log P) and either the electron pair acceptance index or the polarizability.     

The distribution of neuropeptides in the ocular tissues of several mammals: a comparative study.

1. The distribution of several neuropeptides (vasoactive intestinal peptide, substance P, somatostatin and neurotensin) was assessed in ocular tissues from the cow, sheep, rabbit and rat. 2. Vasoactive intestinal peptide was most abundant in the choroid and sclera in all species except the rat. Substance P was most abundant in the retina of cow and rat and in the iris/ciliary body of sheep and rabbit. Somatostatin and neurotensin were most abundant in the retina of all species examined. 3. Regulatory peptides thus display distinct regional distributions within the ocular tissues of a single species of mammal and, in addition, exhibit interspecific variation.