The identification of fibrous proteins in fetal rat epidermis by electrophoretic and immunologic techniques

Two proteins have been identified in extracts of fetal rat skin which are related to the two major fibrous proteins of newborn rat stratum corneum. The relative amount of these proteins increases daily from the 16th to the 20th day (d) of gestation when judged by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis and immunoelectrophoresis using antibody to the purified fibrous protein. Two-dimensional analysis by SDS-polyacrylamide gel electrophoresis and immunoelectrophoresis demonstrates that these two proteins are the only cross-reactive species in the fetal skin from 16d to 19d development. Some additional lower-molecular-weight components can be detected at 20d and 21d. In double-diffusion analysis, cross-reactive proteins in 19d fetal extracts show partial identity but have fewer antigenic sites than proteins in 20d extracts. The 20d protein shows a reaction of identity with purified newborn fibrous protein. Immunofluorescence studies on fetal skin support the prescence of cross-reacting components at 16d development related to the newborn fibrous protein. Intensity of fluorescence increases at 18d and 20d in the spinous and granular cell cytoplasm and in the keratohyaline granules. The stratum corneum, first seen at 20d, is intensely fluorescent. The cellular localization and time of appearance of the cross-reactive proteins suggest that they may be associated with tonofilaments.

Purification and characterization of shikimate kinase enzyme activity in Bacillus subtilis

In Bacillus subtilis shikimate kinase enzyme activity can be demonstrated when a small polypeptide forms a trifunctional complex with the bifunctional enzyme 3-deoxy-D-arabinoheptulosonate-7-phosphate synthetase-chorismate mutase. The shikimate kinase polypeptide whoch carries the catalytic site has been purified to homogeneity by a five-step procedure. The skikimate kinase was determined to have a molecular weight of 10,000 by superfine Sephadex G-75 thin layer chromatography and by calculation of the minimum chemical molecular weight from its amino acid composition. This number corresponds closely to the molecular weight determined by the mobility of the protein following electrophoresis on polyacrylamide gels containing sodium dodecyl sulfate. The enzyme aggregates with itself forming larger molecular weight proteins. Thes aggregational pattersn depend on protein concentration and sulfhydryl bridges. The enzyme activity is completely inhibited by EDTA and the requirement for Mg2+ can be partially replaced by Mn2+, Ca2+, and Co2+. The inhibition of shikimate kinase activity by p-hydroxymercuribenzoate is reversed completely when the enzyme complex is treated with dithiothreitol, suggesting the sulfhydryl groups may be involved with the active site. The trifunctional complex is relatively unstable, and the nonidentical subunits dissociate readily. This dissociation results in a 99% loss in shikimate kinase activity and a 30% decrease in the chorismate mutase-DAHP synthetase activities. Shikimate kinase activity is subject to a variety of controls. It is inhibited by the allosteric effectors chorismate and prephenate, the products of the reaction, ADP, and shikimate 5-phosphate. The activity responds to changes in the energy charge of the cell. Because of the variety of controls exerted on this enzyme, this member of the regulatory complex may represent the key enzyme in the allosteric control of the synthesis of the common precursors of aromatic acid synthesis.

Interaction of phospholipid vesicles with cultured mammalian cells. II. Studies of mechanism

The mechanism of interaction of artificially generated lipid vesicles (approximately 500 A diameter) with Chinese hamster V79 cells bathed in a simple balanced salt solution was investigated. The major pathways of exogenous lipid incorporation in vesicle-treated cells are vesicle-cell fusion and vesicle-cell lipid exchange. At 37 degrees C, the fusion process is dominant, while at 2 degrees C or with energy depleted cells, exchange of lipids between vesicles and cells is important. The fusion mechanism was demonstrated using vesicles of [14C]lecithin containing trapped [13H]inulin. Consistent with a fusion hypothesis, both components became cell associated at 37 degrees C in nearly the same proportions as they were present in the applied vesicles. Additional arguments in favor of vesicle-cell fusion and against phagocytosis or adsorption of intact vesicles are presented. At 2 degrees C or with inhibitor-treated cells, the [3H]inulin uptake was largely suppressed, while the lipid uptake was reduced to a lesser extent. Evidence for vesicle-cell lipid exchange was obtained using V79 cells grown on 3H precursors for cellular lipids. [14C]lecithin vesicles, incubated with such cells, showed no change in their elution properties when subjected to molecular sieve chromatography on Sepharose 4B. However, radioactivity and thin-layer chromatographic analyses revealed that a variety of cell lipiids had been exchanged into the uniamellar vesicles. Further evidence for the fusion and exchange processes was obtained using vesicles prepared from mixtures of [3H]lecithin and [14C]cholesterol. A two-step fusion mechanism consistent with the present findings is proposed as a working model for other fusion studies.

Interaction of phospholipid vesicles with cultured mammalial cells. I. Characteristics of uptake

The interaction of monolayer cultures of Chinese hamster V79 cells with artificially generated, unilamellar lipid vesicles (approximately 500 A diameter) was examined. Vesicles prepared from a variety of natural and synthetic radiolabeled phosphatidyl cholines (lecithins) were incubated with V79 cells bathed in a simple balanced salt solution. After incubation, the cells were analyzed for exogenous lipid incorporation. Large quantities (approximately 10(8) molecules/cell/h) of lecithin became cell associated without affecting cell viability. The effects of pH, charged lipids, and the influence of the vesicle lipid phase transition on the uptake process were examined. Glutaraldehyde fixation of cells before vesicle treatment, or incubation in the presence of metabolic inhibitors, failed to reduce the lecithin uptake by more than 25-50%, suggesting that the lipid uptake is largely energy independent. Cells in sparse culture took up about ten times more lipid than dense cultures. Prolonged incubation (greater than 15 h) of sparse cell cultures with lecithin vesicles resulted in significant cell death while no deleterious effect was found in dense cultures, or with 1:1 lecithin/cholesterol vesicles. When vesicle-treated cells were homogenized and fractionated, about 20-30% of the exogenous lipid was found in the plasma membrane fraction, with the remainder being distributed into intracellular fractions. Electron microscope radioautography further demonstrated that most of the internalized lipid was present in the cytoplasm, with little in the nucleus. These results are discussed in terms of possible modification of cell behavior by lipid vesicle treatment.

Lipid and temperature dependence of membrane-bound ATPase activity of Acholeplasma laidlawii

Arrhenius plots (15–45 °C) of the ATPase activity of Acholeplasma laidlawii membranes enriched with either arachidoyl or saturated short-chain groups exhibited a pronounced discontinuity in slope around 25–30 °C, absent in oleoyl-enriched membranes. The membrane lipid fluidity was measured with a stearic acid spin label. At the growth temperature (37 °C) the membrane lipid fluidity was identical for all three kinds of enriched membranes. For membranes enriched with saturated acyl chains, a plot of the electron paramagnetic resonance anisotropy parameter 2T11vs. the reciprocal of temperature showed a biphasic profile with a discontinuity in slope around 25–30 °C. For oleoyl-group enriched membranes this plot yields only a straight line between 15 and 50 °C. Thus, lipids do play a role in the functioning of the membrane-bound ATPase. This enzyme is probably localized in the more fluid regions of the membrane.

Effect of fatty acyl chain length on some structural and functional parameters of Acholeplasma membranes

Two membrane preparations from Acholeplasma laidlawii were obtained by supplementing the growth media with either arachidic or lauric acid. The cells grown with arachidic acid supplementation yielded membrane lipids greatly enriched with the arachidoyl group and those supplemented with lauric acid yielded membrane lipids enriched with lauroyl, myristoyl, and palmitoyl groups. The cell size (0.1–0.7 μm), the membrane thickness (70 ± 14 Å), and the cell shape (coccoid) showed no difference for these two preparations. The arachidoyl-enriched membrane had a greater buoyant density (1.195 g/ml vs. 1.189 g/ml), a smaller permeability to glycerol, and a greater sensitivity to osmotic shock compared to the membrane enriched with shorter acyl groups. The spin label 2-(10-carboxydecyl)-2-hexyl-4,4-dimethyl-3-oxazolidinyloxyl is less mobile in the arachidoyl-enriched membrane (rotational correlation time at 22 °C, τc = 10 ns) than in the shorter acyl groups enriched membrane (τc = 6 ns). This difference in apparent membrane fluidity can account for the differences observed for the membrane properties.