Effect of water potential on seed germination

The response of seed germination to substrate water potential was determined for several plant species of the arctic tundra. Seeds were collected from Cape Thompson and Eagle Summit, Alaska and germinated on dialysis membranes over water solutions of polyethylene glycol with osmotic potentials of 0 to −6 bars. Germination did not occur with potentials below −3 bars, except for three fellfield species. Germination was delayed at lower osmotic potentials. Because the response of most species was similar, substrate water potential is probably not a factor affecting the establishment of most tundra plant species from seeds.     

Serum lipoproteins and albumin in the lecithin: Cholesterol acyltransferase reaction

The unique features of pig ovarian follicular fluids, i.e., presence of high density lipoprotein (HDL) only and lecithin: cholesterol acyltransferase (EC 2.3.1.43; LCAT) activity, provides a good model to study the effect of serum lipoproteins and serum albumin on the LCAT reaction. $\text{In}\text{vitro}$ cholesterol esterification is enhanced when very low density lipoprotein (VLDL) and low density lipoprotein (LDL) fractions are added, but is inhibited when one or the other of these lipoproteins is absent. High concentrations of HDL₂ result in decreased activation which can be compensated for by the addition of the VLDL-LDL mixture. These findings suggest that the rate of cholesterol esterification in ovarian follicular fluid may be enhanced by providing the exogenous VLDL and LDL as the recipients of HDL-cholesteryl ester. The inhibition of LCAT activity caused by free fatty acid and lysophosphatidylcholine can be partially reversed by the addition of serum albumin, suggesting that serum albumin may regulate the LCAT reaction.     

Rapid and efficient separation and identification of the two molecular forms of human adenosine deaminase by thin-layer gel filtration chromatography

Two molecular forms of adenosine deaminase have been found in human tissues. The column gel filtration method has been used for the separation of the two enzyme forms. Routine separation and analysis of the enzyme forms based on the molecular size difference can be achieved by thin-layer gel filtration on Sephadex G-200 superfine gel. The thin-layer method has been found to be more rapid and efficient than the column method. Enzymes in crude preparations can be studied effectively with the thin-layer method.     

Intracellular localization of GDP-l-fucose: Glycoprotein and CMP-sialic acid: Apolipoprotein glycosyltransferases in rat and pork livers

A GDP-l-fucose:glycoprotein fucosyltransferase which transfers l-fucose to terminal β-N-acetyl-d-glucosaminyl residues of sialidase-, β-galactosidase-treated α₁-acid glycoprotein and a CMP-sialic acid:glycoprotein sialyltransferase acting on sialidase-treated apolipoprotein-Ala₁ from human very low density lipoprotein have been shown to be concentrated in rat liver Golgi apparatus preparations at enrichments of 40- and 45-fold, respectively, and in pork liver Golgi-rich fractions at enrichments of 35- and 20-fold, respectively. A second fucosyltransferase acting on sialidase-treated α₁-acid glycopretein was absent from rat liver and was enriched only 13-fold in a pork liver Golgi-rich fraction. The smooth-surfaced microsome fraction was the only other rat liver subcellular fraction with appreciable levels of the GDP-l-fucose: β-N-acetyl-d-glucosaminide fucosyltransferase and the lipoprotein sialyltransferase (enrichments of 2.6- and 5.2-fold, respectivley). This enrichment could not be attributed to the plasma membrane content of the smooth microsome fraction since plasma membrane fractions from rat liver were shown to have relatively low concentrations of these two transferases (enrichments of 0.3 or less). Rat liver plasma membrane was also shown to have similarly low relative specific activities for three other glycosyltransferases (sialyl-, galactosyl-, and N-acetylglucosaminyl-). The accurate determination of the glycosyltransferase activities of the plasma membrane fraction required the use of relatively low concentrations of plasma membrane and relatively high concentrations of nucleotide-sugars in order to avoid interference by the high nucleotide-sugar pyrophosphatase and hydrolase activities of this fraction.     

Mapping of a new hem gene in Escherichia coli K12.

A new type of haem-deficient mutant was isolated in Escherichia coli K12 by neomycin selection. The mutant, designated SASX38, accumulated uroporphyrin, coproporphyrin and protoporphyrin. Since it possessed normal ferrochelatase activity, it was assumed to be deficient in protoporphyrinogen oxidase activity. The gene affected in the mutant was designated hemG. Mapping of the hemG gene by phage P1-mediated transduction showed that it was located very close to the chlB gene (frequency of cotransduction 78.7%), between the metE and rha markers. This location is distinct from the other known hem loci in E. coli K12.     

FRET-FLIM Investigation of PSD95-NMDA Receptor Interaction in Dendritic Spines; Control by Calpain,CaMKII and Src Family Kinase

Little is known about the changes in protein interactions inside synapses during synaptic remodeling, as their live monitoring in spines has been limited. We used a FRET-FLIM approach in developing cultured rat hippocampal neurons expressing fluorescently tagged NMDA receptor (NMDAR) and PSD95, two essential proteins in synaptic plasticity, to examine the regulation of their interaction. NMDAR stimulation caused a transient decrease in FRET between the NMDAR and PSD95 in spines of young and mature neurons. The activity of both CaMKII and calpain were essential for this effect in both developmental stages. Meanwhile, inhibition of Src family kinase (SFK) had opposing impacts on this decrease in FRET in young versus mature neurons. Our data suggest concerted roles for CaMKII, SFK and calpain activity in regulating activity-dependent separation of PSD95 from GluN2A or GluN2B. Finally, we found that calpain inhibition reduced spine growth that was caused by NMDAR activity, supporting the hypothesis that PSD95-NMDAR separation is implicated in synaptic remodeling.     

HIV Sexual Transmission Is Predominantly Driven by Single Individuals Rather than Discordant Couples: A Model-Based Approach

Understanding the relative contribution to HIV transmission from different social groups is important for public-health policy. Information about the importance of stable serodiscordant couples (when one partner is infected but not the other) relative to contacts outside of stable partnerships in spreading disease can aid in designing and targeting interventions. However, the overall importance of within-couple transmission, and the determinants and correlates of this importance, are not well understood. Here, we explore how mechanistic factors – like partnership dynamics and rates of extra-couple transmission – affect various routes of transmission, using a compartmental model with parameters based on estimates from Sub-Saharan Africa. Under our assumptions, when sampling model parameters within a realistic range, we find that infection of uncoupled individuals is usually the predominant route (median 0.62, 2.5%–97.5% quantiles: 0.26–0.88), while transmission within discordant couples is usually important, but rarely represents the majority of transmissions (median 0.33, 2.5%–97.5% quantiles: 0.10–0.67). We find a strong correlation between long-term HIV prevalence and the contact rate of uncoupled individuals, implying that this rate may be a key driver of HIV prevalence. For a given level of prevalence, we find a negative correlation between the proportion of discordant couples and the within-couple transmission rate, indicating that low discordance in a population may reflect a relatively high rate of within-couple transmission. Transmission within or outside couples and among uncoupled individuals are all likely to be important in sustaining heterosexual HIV transmission in Sub-Saharan Africa. Hence, intervention policies should be broadly targeted when practical.