Paleolimnology of the Peten Lake District,Guatemala

Long-term changes of sedimentary particle-size distribution in two tropical lowland lakes were compared with changes of human population sizes, estimated archaeologically, in the drainage basins. Mean particle size of silt and clay fractions (<64 µm) varied between 3 and 15 µm. High positive skewness and kurtosis of the distributions were associated with smaller particle sizes; hence small mean size resulted from greater influx of small particles while influx of larger particles was probably constant. An inverse correlation between mean particle size and human population size is interpreted to mean that disturbance-induced erosion results in delivery of very fine inorganic particles at higher rates. Within any one basin, particle-size stratigraphy is more precisely related to archaeological time periods than is pollen stratigraphy. An absolute chronology still eludes us, owing to the failure of ¹⁴C dating of calcareous, colluvial sediments, but our relative chronology is now more precise than before. If certain assumptions about past hydrologic relations can be met, particle-size analysis is a way of comparing the histories of geographically very different lakes, including lakes from tropical, temperate, and arctic regions.     

From synthetic antigens to synthetic vaccines

The availability of synthetic antigens permitted a systematic elucidation of the molecular basis of antigenicity, as well as of other phenomena, and to establish the genetic control of immune response and its link to the major histocompatibility region of the species. Moreover, it allowed a conceptual approach to production of vaccines made up of synthetic fragments of relevant virus antigens. This was first demonstrated with a bacteriophage, MS-2, that can be efficiently inactivated with antibodies obtained with an immunogen in which a synthetic peptide corresponding to a sequence of 20 amino acid residues within its coat protein was covalently linked to a polymeric synthetic carrier. When the synthetic adjuvant N-acetyl-muramyl-L-alanyl-D-isoglutamine (MDP) was chemically linked to the same molecule, the resulting immunogen was effective in aqueous solution. This approach has now been used for diphtheria: a synthetic peptide from the A-chain of the toxin, covalently attached together with MDP to the synthetic carrier multichain poly(DL-alanine) induced antibodies cross-reactive with the diphtheria toxin as well as protection against the dermonecrotic activity of the toxin. A similar approach has been described also by R. Arnon and her colleagues in our laboratory for influenza virus, making use of a peptide with sequence 91–108 of the hemagglutinin of type A H₃N₂ strains attached to tetanus toxoid. The results indicated that the conjugate led to partial protection against A/Texas mouse-adapted influenza virus.     

Cell Surface Sialoglycoproteins of Cultured Rat Cerebellar Interneurons

Abstract: The sialoglycoproteins of cultures of relatively pure rat cerebellar interneurons were labelled by NaIO₄ oxidation/NaB ³H₄ reduction. The labelled molecules were analysed by polyacrylamide gel electrophoresis in sodium dodecyl sulphate followed by fluorography. Faint labelling could be detected in three components if cells were labelled without any oxidation. In young cultures, oxidation by galactose oxidase alone failed to reveal any additional bands. After oxidation by NaIO₄ or galactose oxidase in the presence of neuraminidase, many more components were labelled. After NaIO₄ oxidation, about 80% of the cell-associated radioactivity could be removed by treating the cells with neuraminidase, which left the cells more than 95% viable. The majority of the bands seen after neuraminidase treatment were substantially reduced when compared with untreated controls, supporting a surface localisation of these molecules. Reproducible developmental changes were seen in the profiles of bands labelled by NaIO₄/NaB ³H₄ in time course studies of cultures up to 8 days in vitro . Some bands became more prominent, and others disappeared. The gel profiles of the neuron cultures were quite distinct from those of cerebellar astrocyte cultures, which contain all the cell types likely to be contaminants of the neuron cultures.     

Glycosyl acceptors in intact and permeabilized normal and cystic fibrosis fibroblasts

Using cell permeabilization, a technique which allows addition of exogenously supplied radiolabeled sugar nucleotides to serve as direct glycosyl donors, oligosaccharide biosynthesis was examined in fibroblasts obtained from normal and cystic fibrosis (CF) subjects. Incubation of logarithmically growing cells with either radiolabeled leucine or xylose has indicated that there was a difference in the synthetic rate between the cell types. Protein synthesis in normal cells made permeable with 50 m?g/ml lysolecithin (LL) was demonstrated to be absent, and could not be induced to take place by adding exogenous components, including energy sources and amino acids, normally required for protein synthesis. Thus radiolabeled sugars were being added to peptide acceptors which were already present at the time of LL addition. Both permeable and intact fibroblasts were exposed to labeled UDP-xylose, UDP-galactose, and UDP-glucuronic acid, all donors of mucopolysaccharide precursors. The uptake of xylose into protein was the same for both normal and CF cells, but permeable CF fibroblasts incorporated statistically greater amounts of sugar from UDP-galactose and UDP-glucuronic acid. Intact CF cells were also labeled using these two sugar nucleotides. Trypan blue exclusion indicated CF and normal fibroblasts were equally intact. This and the fact that preincubation of CF cells with the appropriate cold sugar nucleotide eliminated the differences in incorporation between the normal and CF cells suggested that CF fibroblasts had more cell surface acceptor than the normal cells.     

Clinical trial of chromium and yeast supplements on carbohydrate and lipid metabolism in diabetic men

Chromium (Cr) deficiency in experimental animals and in humans sustained by prolonged total parenteral nutrition has been shown to cause diabetes mellitus. Prior trials in humans indicated that Cr supplements, in either inorganic or organic form, may improve carbohydrate utilization. We report here a clinical double-blind, random cross-over trial of inorganic chromium trichloride, a brewer’s yeast that contained Cr as glucose-tolerance-factor (GTF), a brewer’s yeast extract without GTF, and a placebo. Forty-three outpatient diabetic men received three of these supplements for 4 months each. Subgroups included 21 ketosis-prone, 7 ketosis-resistant non-obese, and 15 ketosis-resistant obese men. Cr levels were followed pre- and post-treatment in hair, red blood cells, plasma, and urine. Response of carbohydrate metabolism to treatment was assessed in terms of change in insulin requirements, fasting plasma glucose, plasma cholesterol, and triglycerides, as well as the change in plasma glucose, glucagon, and insulin or C-peptide levels in response to a standard meal. In some men, these parameters were also measured after iv tolbutamide. Both the inorganic and organic oral Cr supplements increased measurable body pools of Cr in hair and red blood cells by about 25%. However, fasting plasma glucose and lipids and the glucose response to either the standard meal or to tolbutamide were not significantly altered by any of the treatments.     

Linkage group VI of fish of the genus Xiphophorus (Poeciliidae): Assignment of genes coding for glutamine synthetase,uridine monophosphate kinase,and transferrin

Electrophoretic variation ascribable to three protein-coding loci, coding for glutamine synthetase (GS), uridine monophosphate kinase (UMPK), and transferrin (Tf), was observed in three species of fish of the genus Xiphophorus. Electrophoretic patterns in interspecific F1 hybrid heterozygotes suggested monomeric subunit structures of UMPK and Tf and a multimeric structure of undetermined subunit number of GS. Linkage analyses in backcross hybrids indicated a recombination map of GS-0%-Tf-10.8%-UMPK. This group (designated Xiphophorus linkage group VI) was shown to assort independently from the 14 enzyme loci assigned to linkage groups I-V and from 19 other informative markers within the limits of the data.     

Temperature Control of Phospholipid Biosynthesis in Escherichia coli

The higher the growth temperature of Escherichia coli cultures the greater is the proportion of saturated fatty acids in the bacterial phospholipids. When fatty acids are exogenously supplied to E. coli, higher growth temperatures will likewise increase the relative incorporation of saturated fatty acids into phospholipids. One of the steps in the utilization of fatty acids for phospholipid biosynthesis is, therefore, temperature-controlled. The temperature effect observed in vivo with mixtures of ³H-oleate and ¹⁴C-palmitate is demonstrable in vitro by using mixtures of the coenzyme A derivative of these fatty acids for the acylation of α-glycerol phosphate to lysophosphatidic and phosphatidic acids. In E. coli extracts, the relative rates of transacylation of palmityl and oleyl coenzyme A vary as a function of incubation temperature in a manner which mimics the temperature control observed in vivo. The phosphatidic acid synthesized in vitro shows a striking enrichment of oleate at the β position analogous to the positional specificity observed in phospholipids synthesized in vivo.