FREE-FLOW ELECTROPHORETIC SEPARATION AND ELECTRICAL SURFACE PROPERTIES OF SUBCELLULAR PARTICLES FROM GUINEA PIG BRAIN

Continuous free-flow electrophoretic separation has been used to obtain relatively pure preparations of synaptosomes and synaptic vesicles from crude fractions of guinea pig brain homogenates. Measurements of the contents of protein, neuraminic acid, and bound acetylcholine; the activities of succinic dehydrogenase, adenosine triphosphatase, choline acetylase, and 5'-nucleotidase; and the uptake of ¹⁴C-labeled choline arid acetylcholine in the presence and absence of hemicholinium, all confirm the electron microscope evidence that the electrophoretic preparations are at least as pure as those obtained by ultracentrifugal methods. The electrophoretic mobility measurements have been used to calculate zeta potentials and surface charge densities for these particles.     

Enzymatic aromatization of steroids. I. Effects of oxygen and carbon monoxide on the intermediate steps of estrogen biosynthesis

At Case Western Reserve University in Cleveland, the known intermediate steps in the aromatization, catalyxed by human placental microsomes, of 4-androstene-3, 17-dione to estrone were evaluated. Oxygen and carbon monoxide atmospheres were used to expose the properties of the participating oxidases. The results were judged to be evidence for the existence of 3 mixed function oxidases active in steroid aromatization. One of the oxidases may be a form of cytochrome P-450. The proposed microsomal components must be physically fractionated for validation of their independent existences.     

Hydrolysis of bradykinin and its higher homologues by angiotensin-converting enzyme (Short Communication)

The hydrolysis of bradykinin and its higher homologues by angiotensin-converting enzyme has been investigated by using an automated ninhydrin technique. The results show an inverse relationship of hydrolysis rate with size and charge of the peptide, which parallels the inactivation in the pulmonary circulation and offers an explanation for the selectivity of metabolism of these kinins by the lungs.     

Experiments on resting site selection by nocturnal moths

When different species of moths are presented with a choice between black and white resting backgrounds, there is a strong correlation between the colour selected and the reflectance of the forewings. Under more natural conditions, light-coloured moths usually rest on fresh vegetation whilst dark-winged species select tree bark or rest upon the ground, and different defensive strategies appear to have been adopted by species in these two latter situations. Studies on the mechanism of background selection, and on background selection in polymorphic species, are reviewed.     

Calcium interactions with D-glucans: crystal structure of alpha, alpha-trehalose-calcium bromide monohydrate

Three-dimensional X-ray diffraction data were used to determine the crystal structure of α,α-trehalose-calcium bromide monohydrate, a model system for investigation of factors involved in the binding of calcium ions to d-glucans of dental plaques. Crystals of C₁₂H₂₂O₁₁ ·CaBr₂·H₂O are orthorhombic, space group C222₁, with a  11.058(1) b  11.537(1), c  15.101(1) Å, and Z  4. Intensity data for 925 independent reflections were measured with an automated diffractometer. A trial structure, obtained by the heavy-atom method, was refined by least-squares to R  0.03. An outstanding feature of the crystal packing is the interaction of trehalose molecules with calcium ions. Each calcium is coordinated to hydroxyl groups from four symmetry-related d-glucose moieties, thereby cross-linking the trehalose molecules. Similar interactions between calcium ions and the d-glucose residues of extracellular d-glucans may be of importance in the agglutination processes involved in dental-plaque formation.     

The inhibition of nucleic acid synthesis by mycophenolic acid

1. Mycophenolic acid, an antibiotic of some antiquity that more recently has been found to have marked activity against a range of tumours in mice and rats, strongly inhibits DNA synthesis in the L strain of fibroblasts in vitro. 2. The extent of the inhibition of DNA synthesis is markedly increased by preincubation of the cells with mycophenolic acid before the addition of [(14)C]thymidine. 3. The inhibition of DNA synthesis by mycophenolic acid in L cells in vitro is reversed by guanine in a non-competitive manner, but not by hypoxanthine, xanthine or adenine. 4. The reversal of inhibition by guanine can be suppressed by hypoxanthine, 6-mercaptopurine and adenine. 5. Mycophenolic acid does not inhibit the incorporation of [(14)C]thymidine into DNA in suspensions of Landschütz and Yoshida ascites cells in vitro. 6. Mycophenolic acid inhibits the conversion of [(14)C]hypoxanthine into cold-acid-soluble and -insoluble guanine nucleotides in Landschütz and Yoshida ascites cells and also in L cells in vitro. There is some increase in the radioactivity of the adenine fraction in the presence of the antibiotic. 7. Mycophenolic acid inhibits the conversion of [(14)C]hypoxanthine into xanthine and guanine fractions in a cell-free system from Landschütz cells capable of converting hypoxanthine into IMP, XMP and GMP. 8. Preparations of IMP dehydrogenase from Landschütz ascites cells, calf thymus and LS cells are strongly inhibited by mycophenolic acid. The inhibition showed mixed type kinetics with K(i) values of between 3.03x10(-8) and 4.5x10(-8)m. 9. Evidence was also obtained for a partial, possibly indirect, inhibition by mycophenolic acid of an early stage of biosynthesis of purine nucleotides as indicated by a decrease in the accumulation of formylglycine amide ribonucleotide induced by the antibiotic azaserine in suspensions of Landschütz and Yoshida ascites cells and L cells in vitro.     

Prophylactic Effects of γ-Aminobutyrylhistidine (Homocarnosine) on Experimental Staphylococcal Infections in Mice

Prophylactic administration of the dipeptide homocarnosine induced a high degree of resistance to staphylococcal infections in Swiss albino mice. It expressed its antistaphylococcal properties 1 hr after administration, and this protection lasted for at least 1 month. Although 5 mg per animal (approximately 200 to 250 mg/kg) was routinely used in our studies, experiments showed that comparable results could be obtained with 1.5 mg per animal. Rechallenge experiments indicated that an active infection by itself may confer immunity up to 4 weeks, but an infection after treatment with homocarnosine gave complete immunity to reinfection for at least 2 months. Studies in vitro showed that homocarnosine had no effect on the growth or certain other characteristics (ability to ferment mannitol, liquefy gelatin, and to produce coagulase, deoxyribonuclease, and pigment) of S. aureus. It appears that resistance induced by this peptide is an indirect effect mediated by some nonimmunological host reaction. The possible involvement of homocarnosine, among other compounds, in the protective action of deproteinized beef extract against staphylococcal infections is suggested.