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Biomedical subjects

M Spencer

Publications and source records attributed to M Spencer.

At least 91 records · Page 5Linked to original sources
PubMed1983

A strategy of malaria control.

A field investigation was designed to determine the feasibility of a single annual application of DDT which could fulfil the objectives of malaria control. The concept of a single spraying cycle would eliminate the risks and disadvantages associated with the standard methodology of two spraying cycles, and would result in logistic and economic gains to the country. The timing of the spraying cycle in this modified control methodology is based on the determination of the malaria season solely from entomological data. Details of the field investigation for the years 1974 and 1975, the parameters for calculation of vectorial capacity, estimates of the relative malaria receptivity within the study area, and determination of the malaria season of six months' duration have already been published. The present paper applies the concept of a single spraying cycle to the findings of the investigation and discusses the implementation of the strategy.

Anopheles↗
PubMed1982

Reverse salt gradient chromatography of tRNA on unsubstituted agarose. I. Variations in elution profile and evidence for two fractionation mechanisms.

E. coli tRNA was fractionated by the application of ammonium sulphate reverse gradients to Sepharose 4B. Variations in elution profile were partly attributable to differences between batches of Sepharose. The profile also varied with column length and gradient parameters. This suggests the existence of two distinct mechanisms which do not separate different tRNAs in the same sequence. The first mechanisms, believed to be interfacial precipitation, releases tRNAs progressively as the salt concentration is reduced. A second mechanism introduces adsorptive retardation in which molecules lag behind the solvent. This process, widely believed not to be important in the chromatography of macromolecules with multiple binding sites, is in the present case mainly responsible for the improved resolution of peaks on passage down a long column. Isocratic (constant-salt) fractionation is also feasible. The Sepharose batch variation affects the second mechanism more than the first.

Chromatography, Agarose↗
PubMed1982

Reverse salt gradient chromatography of tRNA on unsubstituted agarose. II. Further study of binding mechanisms.

The existence of two mechanisms in the fractionation of tRNA on Sepharose 4B, using reverse gradients of ammonium sulphate, was confirmed by comparing yeast and E. coli tRNAs, and by extending the range of conditions used. The difference in elution range between the two kinds of tRNA is attributable mainly to variations in tight binding rather than adsorptive retardation. Variations of pH or of temperature produce not only changes in peak distribution, but overall shifts in the elution profile. The shifts correlate closely with changes in the solubility of tRNA in free solution, confirming that tight binding is associated with interfacial precipitation. On the other hand the degree of adsorptive retardation, as indicated by the difference between elution profiles from long and short columns, is quite similar under all conditions. It is if anything slightly greater at 25 degrees C than at 5 degrees C, implying a binding mechanism analogous to hydrophobic bonding. Binding-equilibrium studies suggest that the effect is related to the formation of a monolayer of tRNA on the agarose threads of matrix. Experiments with hydroxyapatite also demonstrate adsorptive retardation, comparable in degree to that observed with Sepharose. This indicates that the effect may be much more important in ion-exchange chromatography than is normally assumed.

Binding Sites↗
PubMed1982

Reverse salt gradient chromatography of tRNA on unsubstituted agarose. III. Physical and chemical properties of different batches of Sepharose 4B.

Four batches of Sepharose 4B, which gave differing elution profiles in reverse salt gradient chromatography of tRNA, were analysed by a number of techniques. Charged groups were estimated from infrared spectra, and gave 0.04-0.05 sulphates and 0.18-0.27 carboxyls per disaccharide. Nuclear magnetic resonance showed the presence of 0.21-0.23 6-O-methyl substituents per disaccharide. The mass concentrations of the beads in aqueous suspension (including agarose-bound water) ranged from 4.7 to 5.0%. High-resolution scanning electron microscopy demonstrated a three-dimensional network of threads with diameters between 2 and 20 nm. None of these properties varied appreciably between batches. There was, however, a variation in the size distribution of beads. In two batches which induced a high degree of adsorptive retardation during chromatography, very few beads exceeded 100 micrometers in diameter; two other batches which gave inferior retardation had a preponderance of somewhat larger beads. The significance of this observation remains unclear.

Chemical Phenomena↗
PubMed1981

The effect of polybrominated biphenyl on infants and young children.

The effects of PBB on 33 children born between September 1, 1973, and December 31, 1975, were evaluated in September, 1977. These children, born to families who lived on quarantined farms, were compared to 20 children who were not exposed to PBB. The birthdate interval was selected to obtain children who were exposed in utero or in early infancy or both, the two time periods when damage to developing tissues and organ systems should have been maximal. The results of these studies failed to identify any effects on physical growth, physical examination, or neurologic assessment, although the parents indicated by historical review that the exposed children had had more illnesses, especially respiratory, than had the control children. There were some indications of an inverse relationship between PBB fast level and performance on selected developmental tests.

Biphenyl Compounds↗
PubMed1980

An octacalcium phosphate intermediate in the synthesis of chromatographic hydroxyapatite.

In the laboratory synthesis of hydroxyapatite for liquid column chromatography different procedures give varying amounts of a transient intermediate, identified by X-ray diffraction as octacalcium phosphate. The intermediate is most abundant in a recently-developed method involving conversion from brushite at neutral pH; well-crystallized hydroxyapatite is then produced without the boiling previously found necessary. The results are relevant to hydroxyapatite biosynthesis, where a similar intermediate has been postulated. Methods are described for the laboratory synthesis of octacalcium phosphate.

Calcium Phosphates↗
PubMed1980

Interparticle effects in low-angle x-ray and neutron diffraction from chromatin.

Published diffraction data are critically reviewed, and replotted in a new way to show the variation with concentration of the 8- to 25- nm diffraction maximum. Most of the early data are found to be consistent with a single model for a liquid-type array of mutually repulsive particles, whose molecular weight is calculated to be that of a nucleosome or possibly a dimer. The data for all but the highest concentrations, where distortion due to dehydration is possible, support no particular model for the higher-order coiling of chains of nucleosomes, and cannot be used to support models for "native" chromatin. Only in the presence of excess salts or after isolation with polyamines is there aggregation in solution of nucleosomes, which then give peaks at 11 and 5.5 nm that do not change much with concentration. Recent work by the authors confirms that under some conditions nucleosome undergo a transition to a state whose diffraction is consistent with hexagonal packing of extended DNA to which histones are still attached. This state is probably responsible for much of the strong 2.7-nm peak previously obtained from certain samples, which was in some cases assigned to nucleosome structure. Only the peak at 3.7 nm is clearly attributable to the form factor of the isolated native nucleosome.

Animals↗
PubMed1980

Biting prevalence and malaria transmission patterns in the Anopheles punctulatus complex (Diptera: Culicidae) in Papua New Guinea.

Seasonal prevalence and malaria transmission patterns of Anopheles farauti, An. punctulatus and An. koliensis were studied in two coastal and two inland villages in the Madang district of northern Papua New Guinea. The monthly manbiting rates (average biting density of vector mosquitoes per man per night) were observed over a two-year period to establish typical seasonal prevalence patterns. Observations on the frequency of feeding and the human blood index were combined to derive the manbiting habit. A daily survival rate was determined from the dissection of mosquito ovaries by Polovodova's age-grading method. The extrinsic cycle in the mosquito was not observed, and the value for this parameter was extracted from the literature. All parameters were combined to estimate the monthly variations in vectorial capacity of each of the vector species, and the vectorial capacities of the individual species were added together to give a total monthly vectorial capacity of the punctulatus complex in each locality. The results showed that malaria transmission can be perennial, with a period of more intense transmission between August and January in the southern area, and between September and February in the northern. A period of very low transmission can be expected between February/March and July/August.

Animals↗
PubMed1980

ATPase Activity of Pea Cotyledon Submitochondrial Particles: ACTIVATION, SUBSTRATE SPECIFICITY, AND ANION EFFECTS.

Submitochondrial particles freshly prepared by sonication from pea cotyledon mitochondria showed low ATPase activity. Activity increased 20-fold on exposure to trypsin. The pea cotyledon submitochondrial particle ATPase was also activated by "aging" in vitro. At pH 7.0 addition of 1 millimolar ATP prevented the activation. ATPase of freshly prepared pea cotyledon submitochondrial particles had a substrate specificity similar to that of the soluble ATPase from pea cotyledon mitochondria, with GTPase > ATPase. "Aged" or trypsin-treated particles showed equal activity with the two substrates. NaCl and NaHCO(3), which stimulate the ATPase but not the GTPase activity of the soluble pea enzyme, were stimulatory to both the ATPase and GTPase activities of freshly prepared submitochondrial particles. However, they were stimulatory only to the ATPase activity of trypsin-treated or "aged" submitochondrial particles. In contrast, the ATPase activity of rat liver submitochondrial particles was stimulated by HCO(3) (-), but inhibited by Cl(-), indicating that Cl(-) stimulation is a distinguishing property of the pea mitochondrial ATPase complex.

Journal Article↗
PubMed1979

Bent DNA.

Explore the source record for details and available documents.

Binding Sites↗
PubMed1979

Oxidative phosphorylation in pea cotyledon submitochondrial particles.

Mitochondria and submitochondrial particles (SMP) from pea cotyledons were shown to catalyze oxidative phosphorylation as measured by (32)Pi uptake into phosphate esters. ATP synthesis was sensitive to the electron transport inhibitor KCN, the uncoupler carbonyl cyanide m-chlorophenylhydrazone, and the coupling factor inhibitor oligomycin. Experiments with the adenine nucleotide translocator inhibitor atractyloside indicated the SMP were inside-out. Mersalyl completely inhibited ATP synthesis by SMP, and a separate experiment indicated that mersalyl has a direct effect on the ATPase complex. The kinetics of ATP synthesis indicated a high affinity for phosphate (K(m) = 0.18 millimolar). ADP kinetics gave a biphasic curve with K(m) values of about 4.8 and 160 micromolar. O(2) uptake and ATP synthesis had a pH maximum of 7.6 while the ratio of micromoles phosphate esterified to microatoms O(2) taken up was highest at pH 7.2. Sodium chloride inhibited both ATP synthesis and O(2) uptake but stimulated the ATPase reaction. The SMP also catalyzed a slow ATP-phosphate exchange reaction.

Journal Article↗