Temperature dependence of chlorophyll {alpha} fluorescence in lettuce and spinach chloroplasts at sub-zero temperatures

The temperature dependence of chlorophyll fluorescence wasmeasured in spinach and lettuce chloroplasts at sub-zero temperaturesin the presence of 50% ethylene glycol. In the presence of 5mM Mg²⁺, a fluorescence maximum appeared at –31?C in boththe spinach and lettuce chloroplasts, while in the presenceof only 5 mM Na⁺ as cations the maximum shifted to –20?Cin the spinach chloroplasts and to –11?C in the lettucechloroplasts. Since the occurrence of a maximum in the temperatureversus fluorescence curve is an indication for the transitionof the physical phase of thylakoid membrane lipids between theliquid crystalline and the phase-separation state (16, 18),these findings suggest that the (major) phase transition ofmembrane lipids occurs at these low temperatures in chloroplastsof higher plants and also that the phase transition temperatureis markedly lowered by the presence of divalent cations. Ethylene glycol at a concentration of 50% had almost no effecton the temperature dependence of chlorophyll fluorescence ina lamellar membrane preparation of Anabaena variabilis. In awater suspension of dimyristoylphosphatidylcholine, the additionof ethylene glycol to 50% did not alter the characteristic featureof the temperature dependence of fluorescence of 1-anilinonaphthalene-8-sulfonate.These findings suggest that 50% ethylene glycol does not affectthe temperature of the transition of the physical phase of membranelipids. ¹ C.I.W.-D.P.B. Publication No. 592. ² Present Address: Department of Biophysics and Biochemistry,Faculty of Science, University of Tokyo, Hongo 113, Tokyo, Japan. (Received June 22, 1977; )     

Glycinebetaine enhances and stabilizes the evolution of oxygen and the synthesis of ATP by cyanobacterial thylakoid membranes.

Glycinebetaine (betaine), an osmoregulant in halophilic plants, stabilized the evolution of oxygen and the synthesis of ATP by thylakoid membranes from the cyanobacterium Synechocystis PCC6803 when it was present during the preparation and incubation of the thylakoid membranes. Moreover, betaine enhanced the evolution of oxygen and the synthesis of ATP when present during assays. When betaine at 1.0 M was present during the preparation of thylakoid membranes and during the measurement of activity, the rate of evolution of oxygen was equivalent to that of intact cells.     

A simple method for the release of asparagine-linked oligosaccharides from a glycoprotein purified by SDS-polyacrylamide gel electrophoresis.

A simple method for the release of oligosaccharides from glycoproteins separated by SDS-polyacrylamide gel electrophoresis (SDS-PAGE) has been developed. Asialo-alpha 1-acid glycoprotein, which was tritiated at the nonreducing terminal D-galactopyranosyl residue by reduction with sodium borotritide after incubation with D-galactose oxidase, was used as a model compound. After electrophoretic separation of the glycoprotein, oligosaccharides were released by the use of a gas-phase hydrazinolysis apparatus. In the first method, the gel was stained with Coomassie Blue and the glycoprotein together with the gel was directly subjected to gas-phase hydrazinolysis after removal of water in a P2O5 desiccator. The recovery of released oligosaccharides was 25.9 +/- 2.4%, based on the amount of the glycoprotein loaded on the gel within the range of 3.5-28.5 micrograms. In the second method, the glycoprotein was electroblotted onto an Immobilon transfer membrane and was visualized by staining with Coomassie Blue. A small piece of the membrane with the corresponding band was cut out, dried in a desiccator and subjected to gas-phase hydrazinolysis. In this case, the recovery of released oligosaccharides was 15.2 +/- 1.0%. These procedures, particularly the first one, should be widely applicable for the isolation of oligosaccharides from glycoproteins separated by SDS-PAGE.     

Crystallization and preliminary X-ray study of the cathepsin B complexed with CA074, a selective inhibitor.

Cathepsin B from bovine spleen has been purified and crystallized as a complex with a specific inhibitor CA074 [N-(L-3-trans-propylcarbamoyloxirane-2-carbonyl)-L- isoleucyl-L-proline], using the hanging-drop method. The complex crystals obtained from 50 mM-citrate buffer (pH 3.5) belong to the tetragonal space group P4(1) (or P4(3)) with a = 73.06 A and c = 141.59 A, and diffract beyond 2.2 A resolution. There are two complex molecules per asymmetric unit giving a packing density of 3.37 A3/Da and indicating a high solvent content of 63.5%.     

Induction of micronucleated reticulocytes by potassium bromate and potassium chromate in CD-1 male mice.

Micronucleus tests of potassium bromate (KBrO3) and potassium chromate (K2CrO4) were conducted with peripheral blood reticulocytes (PB-RETs) of CD-1 male mice dose intraperitoneally. Peripheral blood cells collected from the tail were stained supravitally with acridine orange (AO) using AO-coated glass slides. Both KBrO3 and K2CrO4 induced micronuclei in PB-RETs in the same manner as in polychromatic erythrocytes of bone marrow.     

Genetic Manipulation of the Extent of Desaturation of Fatty Acids in Membrane Lipids in the Cyanobacterium Synechocystis PCC6803

The desA gene of the cyanobacterium, Synechocystis PCC6803,is responsible for the desaturation of fatty acids at the     

A novel fluorescence method to monitor the lysosomal disintegration of low density lipoprotein.

A novel fluorescence method to monitor the lysosomal disintegration of low density lipoprotein (LDL) particles in living cells has been developed. The method is based on the fluorescence resonance energy transfer (RET) between two fluorescent molecules incorporated into LDL particles. NBD-cholesterol linoleate (NBD-CL) and octadecyl rhodamine B (R18) were incorporated simultaneously into LDL, as a RET donor and a RET acceptor, respectively. In this preparation of LDL (RET-LDL), efficient RET was observed, and after the disruption of the LDL particle by a Triton X-100 treatment, the relief of the RET was observed. RET-LDL was endocytosed by CHO cells via LDL receptors, and the RET-LDL particles were disintegrated after the uptake. The resultant relief of the RET upon the disintegration of the LDL was monitored by flow cytometry, and the amount of intact LDL in cells was estimated by calculation. The disintegration occurred with an about 25 min lag, and was inhibited by several lysosomal inhibitors. These results indicate that the disintegration was not a nonspecific event, but took place at the level of lysosomes. Since living cells can be analyzed by the present method, when coupled to flow sorting, it would permit the isolation of cells having different properties in the endocytic pathway of LDL.     

High concentration of a gastrin releasing peptide-like immunoreactive substance in pregnant human milk

The level of a gastrin releasing peptide-like immunoreactive substance (GRP-IS) in human milk and plasma during late pregnancy and after delivery was measured. GRP-IS in milk increased during late pregnancy (1.3 nM at 39 weeks) and decreased after delivery (100 pM). GRP-IS in plasma during late pregnancy and after delivery was much lower (below 2 pM). By using HPLC and gel-filtration chromatography, two peaks of GRP-IS were purified. The one was coeluted with GRP (18-27) and the other was a prohormone. The GRP-IS in milk during pregnancy was mostly composed of proGRP. These results suggest that GRP may be produced and secreted in mammary glands.     

Enhancement of differentiation of rat adipocyte precursor cells by pertussis toxin

To examine whether GTP-binding protein(s) is (are) involved in adipocyte differentiation, the effect of pertussis toxin (PT) was studied in rat adipocyte precursor cell culture. PT potentiated adipose conversion induced by dexamethasone, insulin, and 1-methyl-3-isobutylxanthine in a dose- and time-dependent fashion. Attenuation of an inhibitory control of adenylate cyclase was not the mechanism of action of PT. The dose-dependent inhibition of PT-catalyzed ADP-ribosylation of the Mr 40,000 protein of the cell membrane by preincubation of the toxin was inversely related to the potentiating effect on differentiation. PT-sensitive G protein(s) may be involved in adipocyte differentiation in a negative fashion.