Steady-state kinetics of F1-ATPase. Mechanism of anion activation

The kinetic behaviour of the ATPase activity of beef heart F1 depends largely on the exposure of the enzyme to some anionic ligands such as sulphate and/or EDTA. F1 prepared in the presence of such anions exhibited a triphasic kinetic pattern whereas F1 from which those anions were removed by dialysis exhibited only two Km values for ATP. Conversely to what has been previously reported, bicarbonate did not linearize F1-ATPase kinetics. Moreover, anion activation cannot be simply explained by promotion of ADP release but mainly by an increase in affinity of the third catalytic site for ATP.     

Two-dimensional crystallization of bovine rhodopsin

Bovine rhodopsin has been clustered into two-dimensional crystals in highly purified native rod disk membranes and studied with negative staining and transmission electron microscopy. The lattice is P2(1) with dimensions of 8.3 X 7.9 nm and interaxis angles of 86 +/- 3 degrees. 110 images of ordered areas were digitized and aligned with computer-correlation methods to calculate an average image with diffraction to the fourth order. The images were computer-filtered and reconstructed to approx. 2 nm resolution. When crystals appeared they covered 20-40% of the surface of the preparation and, since rhodopsin is at least 95% of the protein, there is no doubt that the crystals were due to rhodopsin. There appear to be two rhodopsin dimers per unit cell. Each rhodopsin molecules takes up about 7.5 nm2 of membrane area and is estimated to be associated with about 12 lipids on each side of the membrane. The membrane area found for bovine rhodopsin supports the rhodopsin origin of rarely seen but more highly ordered two-dimensional crystals found in detergent-treated frog rod membranes (Corless, J.M., McCaslin, D.R. and Scott, B.L. (1982) Proc. Natl. Acad. Sci. USA 79, 1116-1120). Furthermore, the rhodopsin membrane area is close to that of bacteriorhodopsin and is consistent with a seven transmembrane helix structure proposed for rhodopsin (for references see Dratz, E.A. and Hargrave, D.A. (1983) Trends Biochem. Sci. 8, 128-131). Crystallization was accomplished by lowering the pH to 5.5 near the isoelectric point of rhodopsin, raising the salt concentration of 2 M (NH4)2SO4, adding 5% glucose and 0.02% Hibitane (Ayerst), a cationic amphipathic antiseptic that favored crystal growth.     

A comparison of the receptor constants of morphine and ethylketocyclazocine for analgesia and inhibition of gastrointestinal transit in the rat

The efficacies and dissociation constants of proposed mu and kappa receptor agonists (morphine and ethylketocyclazocine, respectively) were compared using the method of partial irreversible blockade (with buprenorphine) and Stephenson's theory of drug action. While there was good agreement between the dissociation constant (KA) of morphine in analgesia (3.3 x 10(-5) M) and in inhibition of gastrointestinal transit (1.1 x 10(-5) M), the KA of ethylketocyclazocine differed by an order of magnitude in these endpoints (3.2 x 10(-6) M and 6.7 x 10(-5) M, respectively). The efficacies of morphine were found to be similar for the two effects studied (4.23 and 5.26), while those for ethylketocyclazocine differed markedly (2.06 and 10.39). The fraction of receptors remaining unblocked after buprenorphine was consistent for the test but not for the agonist, indicating a different distribution of receptors for the two endpoints. Our results strongly suggest that morphine induces analgesia, and slows transit in the small intestine, through the same type of receptor. The same conclusion cannot be drawn for ethylketocyclazocine.     

Effect of water-soluble antioxidants on the permeability of lysosomal membranes and on the structure of the liver in rats with thermal burns

Experiments on rats were made to study the effect of water-soluble antioxidants on the permeability of lysosomal membranes of liver cells and liver structure under burn. Antioxidants were injected intraperitoneally shortly after burn, whereas examination was performed after one day. It has been discovered that one day after burn there takes place an appreciable destabilization of lysosomal membranes with the release of a lysosomal matrix enzyme, cathepsin D to the cytoplasm. Liver structure had undergone substantial changes by that time. After administration of water-soluble antioxidants lysosomal membranes got stabilized while liver structure manifested but insignificant disorders.     

Immunohistochemical evaluation of ras oncogene expression in pulmonary and pleural neoplasms

We undertook an immunohistochemical analysis of human bronchopulmonary epithelial neoplasms and pleural mesotheliomas using a monoclonal antibody which recognizes ras oncogene products (p21ras). The monoclonal antibody, RAP-5, recognizes both unaltered and certain mutated p21ras. Formalin fixed and paraffin embedded tissue samples of 187 lung epithelial tumors and 27 pleural mesotheliomas were investigated; normal and bronchiectatic lungs were similarly studied. Normal lung and pleural tissue did not immunostain except for occasional type II pneumocytes. Reactive type II pneumocytes adjacent to carcinomas and bronchiectasis immunostained consistently. Twenty four/34 (71%) squamous carcinomas immunostained. Only 8/50 (16%) adenocarcinomas immunostained focally and weakly whereas 19/24 (79%) bronchioloalveolar carcinomas immunostained. Eleven/18 (61%) large cell carcinomas immunostained with variable intensity. Eleven/13 (85%) carcinoids, 6/7 (85%) well differentiated neuroendocrine carcinomas, and 18/21 (86%) intermediate cell neuroendocrine carcinomas immunostained while none of 20 small cell neuroendocrine carcinomas immunostained. Only a few mesotheliomas were immunostained focally. Two/14 (14%) epithelial type and 1/9 (11%) biphasic type mesotheliomas immunostained weakly; none of 4 spindle cell mesotheliomas immunostained. We conclude that while at least occasional cases of most types of pulmonary epithelial neoplasms express p21ras, the frequency and intensity of the expression are distinctly greater in certain tumor types such as squamous, bronchioloalveolar, and neuroendocrine neoplasm except for the small cell type. Contrary to these lung epithelial neoplasms, most mesotheliomas did not immunostain for p21ras. Whether the enhanced p21ras expression may point to a different mechanism of transformation or may merely reflect differentiation features remains undetermined.     

Deoxyuridine triphosphatase: A potential site of interaction with pyrimidine nucleotide analogues

Deoxyuridine triphosphatase has been purified from cultured human lymphoid cells in high yield and stable form by a relatively simple procedure. The properties differed somewhat from those reported previously, e.g. apparent K_m, molecular weight, and effects of divalent metals. No other naturally occurring dNTP or NTP serves as substrate, however, the enzyme may be an important site of interaction with intracellular derivatives of analogues of dUrd. It is shown here that deoxyuridine triphosphatase acts on araUTP, 6-azadUTP, 2′-FdUTP, and 2′,3′-dideoxyUTP, but the enzyme has no effect on 5-C1dUTP, 5-BrdUTP, 5-HgdUTP and dUrd-5′[α-thio]triphosphate. For the preparation of one of the analogues, the enzyme, trans-N-deoxyribosylase, from Lactobacillus, was used to prepare the deoxynucleoside from the base, a procedure that may have general usefulness.     

Effect of mannitol and glucose on the distribution and trypsin susceptibility of protein A of Staphylococcus aureus

The biological activity and morphological distribution of protein A on the cell surface were studied in a medium containing an excess of either mannitol or glucose, which suppressed protein A production of Staphylococcus aureus, Cowan I strain. Preculture of the organisms in the presence of a sugar suppressed the expression of protein A, resulting in a decrease in the number of cells bound with antiferritin rabbit IgG molecules, which specifically indicate protein A distribution. The distribution pattern of protein A on the cell surface changed with glucose but not with mannitol. The two-layered ferritin distribution on the organism grown in the control medium was altered into a heavily labeled, thick and rough layer with glucose, suggesting the induction of a conformational change in the polypeptide chain forming protein A. This was positively supported by the increase in trypsin susceptibility of protein A.     

Spin-label studies on phosphatidylcholine-cholesterol membranes: effects of alkyl chain length and unsaturation in the fluid phase

Dynamic properties of phosphatidylcholine-cholesterol membranes in the fluid phase and water accessibility to the membranes have been studied as a function of phospholipid alkyl chain length, saturation, mole fraction of cholesterol, and temperature by using spin and fluorescence labelling methods. The results are the following: (1) The effect of cholesterol on motional freedom of 5-doxyl stearic acid spin label (5-SASL) and 16-doxyl stearic acid spin label (16-SASL) in saturated phosphatidylcholine membrane is significantly larger than the effects of alkyl chain length and introduction of unsaturation in the alkyl chain. (2) Variation of alkyl chain length of saturated phospholipids does not alter the effects of cholesterol except in the case of dilauroylphosphatidylcholine, which possesses the shortest alkyl chains (12 carbons) used in this work. (3) Unsaturation of the alkyl chains greatly reduces the ordering effect of cholesterol at C-5 and C-16 positions although unsaturation alone gives only minor fluidizing effects. (4) Introduction of 30 mol% cholesterol to dimyristoylphosphatidylcholine membranes decreases the lateral diffusion constants of lipids by a factor of four, while it causes only a slight decrease of lateral diffusion in dioleoylphosphatidylcholine membranes. (5) If compared at the same temperature, 5-SASL mobilities plotted as a function of mole fraction of cholesterol in the fluid phases of dimyristoylphosphatidylcholine-, dipalmitoylphosphatidylcholine- and distearoylphosphatidylcholine-cholesterol membranes are similar in wide ranges of temperature (45-82 degrees C) and cholesterol mole fraction (0-50%). (6) In isothermal experiments with saturated phosphatidylcholine membranes, 5-SASL is maximally immobilized at the phase boundary between Regions I and III reported by other workers (Recktenwald, D.J. and McConnell, H.M. (1981) Biochemistry 20, 4505-4510) and becomes more mobile away from the boundary in Regions I and III. (7) 5-SASL in unsaturated phosphatidylcholine membranes showed a gradual monotonic immobilization with increase of cholesterol mole fraction without showing any maximum in the range of cholesterol fractions studied. (8) By rigorously determining rigid-limit magnetic parameters of cholestane spin labels in membranes from Q-band second-derivative ESR spectra to monitor the dielectric environment around the nitroxide radical, it is concluded that cholesterol incorporation increases water accessibility in the hydrophilic loci of the membrane. In contrast, 12-(9-anthroyloxy)stearic acid fluorescence showed that water accessibility is decreased in the hydrophobic loci of the membrane.