The identification of unbranched enzyme kinetic mechanisms by computer analysis of qualitative information: Logic of the method

The paper describes the logic of a computer method for identifying unbranched enzyme kinetic mechanisms on the basis of observed initial velocity and product inhibition patterns (Cleland, 1963). The method establishes initially an acceptable order of reactant addition and release, proceeds to list all the mechanisms consistent with that order and the data, and finally determines which of these can also explain data which require either non-competitive or dead-end inhibition.     

Steroid hormone receptor studies in melanoma model systems

The Transplantable B-16 melanotic melanoma carried in syngeneic C57B1/6J female mice and the Syrian hamster melanoma cell line, RPMI 3460, were utilized to determine whether steroid-hormone receptors are present in animal melanomas. In the B-16 melanoma, a cytoplasmic-estrogen receptor is detectable, but there is no evidence for androgen or progestin receptors. Some tumors contain a glucocorticoid-binding macromolecule. Sucrosedensity gradient centrifugation of cytosol after incubation with [³H]-estradiol revealed an 8S peak that was suppressed by excess radioinert diethylstilbesterol. Binding varied from 5–35 fmoles per mg cytosol protein. Scatchard analysis of [³H]-estradiol binding in cytosol yielded a single class of high-affinity binding sites; the dissociation constant is 6 × 10^?10 M. The receptor molecule is shown to be estrogen-specific by ligand competition assays. In contrast to B-16 melanoma, no estrogen, androgen, or progestin receptor can be found in the Syrian hamster melanoma cell line. However, a substantial level of specific binding is observed using [³H]-dexamethasone. Sucrose-gradient centrifugation of cytosol from this cell line after incubation with [³H]-dexamethasone revealed a 7S peak that was suppressed by excess radioinert dexamethasone. Scatchard analysis indicated a single class of high affinity sites with a dissociation constant of 2 × 10^?9 M. Binding levels from 70–610 fmoles per mg cytosol protein were observed. The Syrian hamster melanoma cells also exhibit a biological response to glucocorticoids: Dexamethasone causes both an inhibition of growth and a decrease in final-cell density in these cells.     

A new species of Eugenia (Myrtaceae) from Venezuela

Eugenia mcvaughii is described from a forest remnant of the Jardin Botánico of Caracas, Venezuela. Found also in the hills adjacent to Caracas, it may be considered as an endemic species of the Interior Coastal Cordillera.     

New species from the summit of Cerro Guaiquinima,Venezuela

Three new species,Lubaria szczerbanii (Rutaceae),Croton guaiquinimae (Euphorbiaceae), andStomatochaeta colveei (Asteraceae), are described from the summit of Cerro Guaiquinima, Venezuela. The generic affinities betweenLubaria andMyllanthus, and betweenStomatochaeta andStenopadus are discussed.     

Evidence for a multiple innervation of purkinje cells by climbing fibers in the immature rat cerebellum

Climbing fiber (CF)–-Purkinje cell (PC) relationships were studied electrophysiologically on the cerebellum of 8 to 15 day old rats. Some animals were rendered agranular by x-irradiation from birth; some others were treated with 3-acetyl pyridine 3 days before study to selectively destroy the CF. Unitary extracellular recordings in 8–9 day old normal rats revealed that more than 50μ of the PC units each exhibited either two types of all-or-none climbing fiber responses (CFR) or stepwise graded CFRs. The other PC units only presented one type of all-or-none CFR. These activities were entirely mediated via CF since they persisted at the same age in x-irradiated rats, but were absent in animals treated with 3-acetyl pyridine. Interaction experiments were performed between juxtafastigial and Inferior Olive stimulations on 49 PC units in 8–9 day old normal rats. Collisions between impulses set up in CFs were disclosed in 21 out of the 24 PCs which exhibited only one type of CFR. In the three others and in each of the 25 PCs that displayed two types of all-or-none CFRs, or CFRs graded by steps, no collision was detected. Moreover intracellular recordings of epsp's mediated via CFs in PCs of 8–9 day old normal rats revealed that they frequently fluctuated in stepwise fashion. These results demonstrate that in the immature rat more than 50μ of PCs are each innervated by at least two distinct CFs; later on, the disappearance of the supernumerary synapses between CF and PC leads, as early as day 15, to the one-to-one relationship between CF and PC.     

Molecular weight and amino acid composition of purified spinach beet phenolase

The purification of spinach beet phenolase has been modified to include equilibration of the crude macerate with 0.5% cetyl-trimethylammonium bromide a     

Amphiphiles for supercritical CO2

A semi-fluorinated hybrid amphiphile, pentadecafluoro-5-dodecyl (F7H4) sulfate, has been shown to form reversed micelles in dense CO₂; the aggregates evolve to form water-in-CO₂ (w/c) microemulsion droplets on addition of water. Aggregation structures in these w/c phases have been characterised by small-angle neutron scattering (SANS), showing the presence of cylindrical droplets, which change into dispersed lamellar phases at even higher water loadings. Other systems are also introduced, being high internal phase emulsions (HIPEs) with brine, and liquid and supercritical CO₂, stabilized by certain commercially available nonylphenol ethoxylates (Dow Tergitol NP-, and Huntsman Surfonic N- amphiphiles). These dispersions have been characterised by SANS for the first time. Quantitative analyses of the HIPEs SANS profiles show that they behave similarly to hydrocarbon-water emulsion analogues, with regard to total interfacial areas and the effects of amphiphile concentration on the underlying structures. Finally, the advantages and disadvantages of both approaches for controlling the physico-chemical properties of liquid/supercritical CO₂ in potential applications are compared and contrasted. These results highlight the importance of using specially designed CO₂-philic amphiphiles for generating self-assembly structures in dense CO₂.     

Interspecific patterns for egg and clutch sizes of African Bufonidae (Amphibia: Anura)

Little is known about reproductive trade-offs in African amphibians, but such data, particularly in the form of quantitative measurements, are a key for investigating life history evolution. Here we compile and analyze known data on African bufonids from published material and new data from preserved museum specimens, to investigate interspecific patterns of egg and clutch sizes variation. Our data is a composite of mixed sources, including ova data from dissected females and laid clutches from observations in the field. Our study shows that, as body size increases, clutch size increases but egg size decreases, and when correcting for body size, egg size is inversely correlated with clutch size. These parameter interactions however, are different for different reproductive modes. In free-swimming larval developing species, the same trends are recovered, but for lecithotrophic viviparous species no significant correlations could be recovered for clutch size and body size nor for the trade-off between clutch size and egg size, and egg size is positively related to body size. The egg size of Nimbaphrynoides occidentalis (Angel, 1943) is a clear outlier, which may be due to its matrotrophic viviparous reproduction. In addition, we observed no statistical difference between ova data collected from dissections and laid clutch data from field observations, which suggests that such a mixed dataset has utility in comparative analyses.