Visualization of ribosome--single-stranded DNA complexes in the electron microscope.

A procedure is described which allows ribosomes bound to single-stranded DNA to be visualized in the electron microscope. The number of bound ribosomes may be determined and the position of the bound ribosomes may be readily measured along the DNA. The distribution of ribosomes bound to separated l and r strands of lambda DNA was shown to conform to the pattern predicted for binding at specific sites. The procedure should allow mapping of ribosome binding sites for the determination of genetic maps and may also be useful for studying translational control and relative binding affinities for ribosomes.     

Retention of lipolytic products in chylomicrons incubated with lipoprotein lipase: electron microscope study.

Early effects of lipolysis on the structure of chylomicrons in vitro were studied in rat chylomicrons incubated with purified bovine mild lipoprotein lipase at pH 8.1. The amount of the albumin added to the incubation medium was limited so that free fatty acids (FFA) and partial glycerides formed during lipolysis would accumulate in the chylomicrons. The structures visualized in lipolyzed chylomicrons was found to be affected by pH during preparation of specimens for microscopy, whether fixed with OsO4 and sectioned, or stained with sodium phosphotungstate and examined as whole mounts. Circular aqueous spaces were present in the triglyceride core of lipolyzed chylomicrons processed at pH 8.1 and 7.4. Sometimes the spaces contained aggregates of osmiophilic material and whorls of bilayered lamellae. The spaces were replaced by lamellar structures having a periodicity of 40 A, in chylomicrons processed at pH 5.5, and the spaces and lamellae were both absent at pH 3.0. The findings indicate that these spaces were lined by a lipid monolayer which formed bilayered lamellae under certain conditions. It is concluded that the monolayer lining the aqueous spaces is an inward extension of the chylomicron surface film produced by the accumulation and movement of lipolytic products, FFA and partial glycerides, in the interfacial plane between core triglyceride and water.     

Kinetics of electron transfer in macromolecules]

With the help of retarded double-time Green function technique a method of estimation of electron transfer rate in protein macromolecules has been developed. Possible experimental test is suggested.     

On the standardization of electron microscope autoradiography

Some properties of Ilford emulsion L4 monolayers were determined quantitatively using infinitely thick layers of a tritiated polymer as reference radiation sources.     

Locust haemolymph lipoproteins visualised in the electron microscope

Summary In matureLocusta, the haemolymph lipoproteins change both in quality and quantity according to the physiological state of the animal. In resting locusts the majority of lipid in the haemolymph is carried by lipoprotein A_yellow, but during flight or after adipokinetic hormone injection, A_yellow joins together with extra diacylglycerols from the fat body and non-lipid carrying C_L-proteins to form another lipoprotein, A⁺. In this study partially purified A_yellow and A⁺ lipoproteins have been visualised by transmission electron microscopy after negative staining or shadowing. Both A_yellow and A⁺ lipoproteins are discrete particulate structures but they differ markedly in size; A_yellow particles are 9–16 nm in diameter while those of A⁺ are mostly in the range 20–50 nm. Large lipoprotein particles of the A⁺ type have not been described previously in insect haemolymph but, interestingly, the locust A⁺ particles do resemble most closely the low density lipoprotein particles described in human serum by Forte and Nichols (1972).     

Visualization of lipoprotein receptors by ligand blotting

This paper describes the visualization of the low density lipoprotein (LDL) receptor by ligand blotting. Preparations of detergent-solubilized membranes are subjected to one- or two-dimensional sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis, after which the proteins are transferred to nitrocellulose paper. The paper is incubated with native LDL and then with an 125I-labeled antibody against LDL, and the bound antibody is visualized by autoradiography. The success of LDL blotting depends on the omission of sulfhydryl reducing agents from the electrophoresis system. Intrachain disulfide bonds allow the receptor to retain its binding activity even after electrophoresis in the presence of SDS. In identifying LDL receptors, the ligand blotting technique is as sensitive as immunoblotting with a monoclonal antibody against the LDL receptor; it can therefore be used to identify receptors when no anti-receptor antibodies are available. We use this technique to show that the LDL receptor of the rabbit adrenal gland has the same molecular weight as the LDL receptor of the bovine adrenal cortex and human fibroblasts. The ligand blotting technique may be generally applicable for visualization of other plasma membrane receptors after SDS-gel electrophoresis.     

Early metallurgical applications of the electron microscope in Cambridge

A short account of a post-war (1948) survey of electron microscopes in Europe and of work done at Cambridge investigating metal replicas and dislocations in thin specimens.