Caldesmon: A calmodulin — Binding actin — Regulatory protein

The protein caldesmon, originally isolated from smooth muscle tissue where it is the most abundant calmodulin-binding protein, has since been shown to have a wide distribution in actin- and myosin- containing cells where it is localized in sub-cellular structures concerned with motility, shape changes and exo- or endo-cytosis. Caldesmon is believed to be an actin- regulatory protein, and binds with high affinity to actin or actin-tropomyosin. Caldesmon inhibits the activation by actin-tropomyosin of myosin MgATPase activity, and the inhibition can be reversed by Ca2+.calmodulin. The binding of caldesmon to smooth muscle proteins has been studied in detail, enabling a model to be constructed which could account for the observed Ca2+ regulation of smooth muscle thin filaments. The abundance of caldesmon, and the Ca2+-regulation of its activity via calmodulin, mean that it is potentially an important intracellular regulator of processes such as smooth muscle contraction, cell motility and secretion.     

Fatty acids reverse the cyclic AMP inhibition of triacylglycerol and phosphatidylcholine synthesis in rat hepatocytes.

The influence of cyclic AMP analogues and fatty acids on glycerolipid biosynthesis in monolayer cultures of rat hepatocytes was investigated. Chlorophenylthio-cyclic AMP and adenosine 3':5'-cyclic phosphorothioate inhibited the rate of triacylglycerol synthesis from [1(3)-3H]glycerol, and phosphatidylcholine synthesis from [Me-3H]-choline. Supplementation of the hepatocytes with palmitate (1 mM) reversed chlorophenylthio-cyclic AMP inhibition of triacylglycerol synthesis. Similarly, cyclic AMP analogue-inhibition of phosphatidylcholine synthesis was abolished when the cells were simultaneously incubated with oleate (3 mM). Reactivation of phosphatidylcholine synthesis in chlorophenylthio-cyclic AMP-supplemented cells with oleate was accompanied by conversion of CTP: phosphocholine cytidylyltransferase into the membrane-bound form, since these cells released the enzyme more slowly after treatment with digitonin. The opposing actions of cyclic AMP and fatty acids are discussed in relation to the regulation of glycerolipid biosynthesis during starvation, diabetes and stress.     

Fluorouracil and the isolation of mutants lacking uridine phosphorylase in Escherichia coli: location of the gene

Summary A selective technique is described for the isolation of mutants of Escherichia coli lacking uridine phosphorylase and the location of the gene specifying this enzyme on the bacterial chromosome is determined. Using strains with appropriate lesions it is shown that there are three routes via which 5-fluorouracil can be converted to compounds which inhibit cell growth.     

Schiff bases formed from retinal and phosphatidylethanolamine, phosphatidylserine, ethanolamine or serine

1. Conditions were established for the reaction of retinal with phosphatidylethanolamine, phosphatidylserine, ethanolamine and serine in chloroform, ethanol or ethanol–water solutions to form retinylidene compounds, or Schiff bases. 2. The Schiff bases were reduced to retinyl compounds with sodium borohydride. 3. Absorption maxima and molar extinction coefficients were determined for the various retinylidene and retinyl compounds and for the corresponding coloured products formed by their reaction with antimony trichloride.     

A CYTOCHEMICAL STUDY OF EMBRYO SAC DEVELOPMENT IN STELLARIA MEDIA

Megasporogenesis and embryo sac development in Stellaria media were investigated using cytochemical methods for the demonstration of nucleic acids, proteins, and polysaccharides. RNA concentrations were high in the archesporial cells, low in the megaspore mother cell, and increased again to high concentrations with the formation of the megaspore and 2-, 4-, and early 8-nucleate embryo sac. RNA levels were also high in the egg and primary endosperm nucleus but low in the synergid and antipodal cells. Nucleolar size and vacuolation were indicative of RNA synthetic activity. Protein concentrations were parallel in concentration and distribution to those observed for RNA. Polysaccharides were conspicuously absent from all stages except the synergids and nucellar cells. Feulgen-stained DNA was demonstrable in the antipodal cells, megaspore mother cell, and megaspore cell, but was not visible in the 2-, 4-, or early 8-nucleate embryo sac. Feulgen staining was also absent from the egg and primary endosperm nucleus but was visible in the synergids and antipodals. Histones were difficult to visualize anywhere except in the egg cytoplasm and the nuclei of the antipodals.     

Fragile-X syndrome: Unique genetics of the heritable unstable element

The fragile site at Xq27.3 is an unstable microsatellite repeat, p(CCG)n. In fragile-X syndrome pedigrees, this sequence exhibits variable amplification, the length of which correlates with fragile-site expression. There is a direct relationship between increased p(CCG)n copy number and propensity for instability: individuals having large amplifications exhibit somatic variation due to increased instability. The instability of the p(CCG)n repeat, when transmitted through affected pedigrees, explains the unusual segregation patterns of fragile-X phenotype, referred to as the Sherman paradox. All individuals of fragile-X genotype were found (where testing was possible) to have a parent with amplified p(CCG)n repeat, indicating that few, if any, cases of fragile-X syndrome are not familial.     

Cells of the Upper and Lower Epidermis of Barley (Hordeum vulgare L.) Leaves Exhibit Distinct Patterns of Vacuolar Solutes

Vacuolar saps were extracted from individual, anatomically uniform cells of the upper (adaxial) and lower (abaxial) epidermis of the third leaf of barley (Hordeum vulgare L.) using a modified pressure probe. Saps (volume 80-200 pL) were sampled at various times between 3 d before and 7 d after full-leaf expansion and were analyzed for their osmolality and their concentrations of NO3-, malate, CI-, K+, and Ca2+. The osmolalities of upper and lower epidermis both increased with time but were similar to each other. In young leaves, K+ and Ca2+ were evenly distributed between the two epidermal layers, but as the leaf aged, the upper epidermis accumulated high (40-100 mM) Ca2+, whereas cells of the lower epidermis accumulated K+ instead. Nitrate concentration was 100 to 150 mM higher in the upper than in the lower epidermis, whereas CI- was 50 to 120 mM higher in the lower epidermis. These differences did not depend on the leaf developmental stage. The uneven distribution of epidermal NO3- and CI- was maintainedover a wide range of epidermal sap concentrations of these ions and was not affected by NO3- or CI- starvation or by an increase in the light intensity from 120 to 400 [mu]mol m-2 s-1. However, the latter did cause a decrease in epidermal NO3- and the appearance and accumulation of epidermal malate, particularly in the upper epidermis. The physiological implications of the results for solute storage in leaves and for the pathways of ion distribution to the epidermis are discussed.