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121.
122.
123.
Mag. rer. nat. Alois Lametschwandtner Peter Simonsberger Hans Adam 《Cell and tissue research》1977,180(4):433-442
The angioarchitecture of the neural stalk and the encephaloposthypophysial portal system of the hypophysis of the toad, Bufo bufo (L.), was studied using three different methods. The neural stalk is mainly supplied by branches of the arteria infundibularis superficialis which form a widemeshed vascular network. Dorsally this network continues into the plexus of the pars nervosa. The vascularization of the pars nervosa is made up of the encephalo-posthypophysial portal system. This portal system consists of a hypothalamic branch (=portion), a mesencephalic and a mesencephalicbulbar branch (=portion). The hypothalamic branch was found to drain the pars ventralis of the tuber cinereum as well as more dorsal regions of the diencephalon. The mesencephalic-bulbar trunk enters the hypothalamic branch. The resulting common stem of the encephalo-posthypophysial portal vein the curves around the retroinfundibular communicating artery, crosses its ventral side and runs caudally. The secondary capillary plexus of the pars nervosa is characterized by well defined capillary plexus of the pars nervosa is characterized by well defined capillary networks which are located at the periphery of the parenchyma of the pars nervosa, thus forming a rostral, dorsal and ventro-caudal net. The central region of the parenchyma of the pars nervosa is supplied only by main branches of the encephalo-postpophysial portal vein. The venous drainage of the pars nervosa is via the vena hypophysea transversa. 相似文献
124.
Adam Zipp Irwin D. Kuntz Thomas L. James 《Archives of biochemistry and biophysics》1977,178(2):435-441
The dependence of the water proton magnetic resonance spin-lattice relaxation rate (T1??1) in the rotating frame on the strength of the spin-locking (H1) field has been investigated for packed oxy and deoxy normal and sickle erythrocytes at temperatures from 9 to 40 °C. The T1??1 of oxy or deoxy normal erythrocytes shows no dependence on H1 up to ~7 G at any temperature studied. On the other hand, T1??1 decreases from about 40 s?1 to 15 s?1 (H1 from 0 to ~7 G) for deoxygenated packed sickle cells at 40 °C. The magnitude of this variation of T1??1 with H1 decreases with decreasing temperature. Oxy packed sickle cells also show a dependence of T1??1 on H1 but the magnitude is <10% of that of the deoxygenated samples. These results suggest that water proton T1??1 measurements are a sensitive probe of hemoglobin S polymerization and provide a novel technique for the study of slow water motions in these systems. The T1??1 results are compared with low frequency T1?1 results of other investigators on hemoglobin S solutions. Analysis of the data suggests that water proton motions with correlation times of the order of 10?5 s are present in the deoxygenated sickle cell samples at temperatures above 10 °C. 相似文献
125.
126.
R R Drake P Zimniak B E Haley R Lester A D Elbein A Radominska 《The Journal of biological chemistry》1991,266(34):23257-23260
A new active site-directed photoaffinity analogue, [beta-32P]5-azido-UDP-glucuronic acid (UDP-GlcA), was enzymatically synthesized from [beta-32P]5-N3UDP-Glc using UDP-glucose dehydrogenase. The product was characterized by its mobility on ion exchange and two thin-layer chromatographic systems, by its UV absorbance at 288 nm, and the loss of this absorbance after UV irradiation of the compound. Photoincorporation of [beta-32P]5-N3UDP-GlcA into bovine liver UDP-Glc dehydrogenase (EC 1.1.1.22) was saturable with an apparent Kd of 12.5 microM, and was inhibited by the known active-site effectors UDP-GlcA, UDP-Glc, and UDP-xylose. When human liver microsomes with known UDP-glucuronosyltransferase (EC 2.4.1.17) activities were photolabeled with [beta-32P]5-N3UDP-GlcA, major photolabeled bands of 35-37 and 50-54 kDa were detected. When rat liver microsomes from phenobarbital-injected rats were photolabeled with [beta-32P]5-N3UDP-GlcA, there was a marked increase in photoincorporation of a 51-kDa protein as compared with control animals. Evidence is presented which suggests that the photolabeled 51-54-kDa proteins in the liver microsomes from both tissues are UDP-glucuronosyltransferase and that [beta-32P]5-N3UDP-GlcA represents a new alternative approach in the study of UDP-glucuronosyltransferase and other UDP-GlcA-utilizing enzymes. 相似文献
127.
Composition and seasonal fluctuations of the ichthyoplankton community in a shallow tidal channel of Cadiz Bay (S.W. Spain) 总被引:4,自引:0,他引:4
The composition and seasonal variation of the ichthyoplankton community in a shallow tidal channel in Cadiz Bay was studied for 5 years (1984 1988), taking fortnightly samples with a conical tide-strained net (0.5 mm mesh). Thirty-nine species belonging to 21 families of teleosts were caught. Four species ( Pomutoschistus microps Kroyer, Atherina hoyeri Risso, Liza rumuda Risso and Lizu a lira Ia Risso) totalled more than 90% of the annual ichthyoplankton abundance. Three species, assumed to be permanent residents, dominated the number offish (837%), and were represented by all their developing stages; 26 species (66.7%) were temporary residents, contributing 17.2% to the total abundance and were represented only by early developing stages; the remaining 10 species were classified as rare. Monthly numbers of species and individuals showed seasonal variation with a main annual peak in spring and in late spring-early summer, respectively. The diversity (H') and evenness (S) indices of this community were low (0.13 to 1.83 and 0.03 to 0.71. respectively), with higher values in winter and late summer, and both were significantly correlated with the log-transformed density of temporary residents (r = 0.43 and 0.41, respectively; P<0.0l) and permanent residents (r=−0.75 and −0.79, respectively; P<0.01). Multivariate classification analysis of samples revealed that similar cyclical changes were taking place in the structure of this ichthyoplankton community every year; three periods could be differentiated: (1) a cool period of low fish density but relatively high diversity; (2) moderate temperature and salinity with high numbers of species and density but low diversity and (3) a warm period of moderate diversity and fish density. 相似文献
128.
Left handed alpha-helix formation by a bacterial peptide 总被引:2,自引:0,他引:2
The alpha-helix is a common element of secondary structure in proteins and peptides. In eukaryotic organisms, which exclusively incorporate L-amino acids into such molecules, stereochemical interactions make such alpha-helices, invariably right-handed. Pseudomonas tolaasii Paine is the causal organism of the economically significant brown blotch disease of the cultivated mushroom Agaricus bisporus (Lange) Imbach. P. Tolaasii proceduces an extracellular lipodepsipeptide toxin, tolaasin, which causes the brown pitted lesions on the mushroom cap. Circular dichroism studies on tolaasin in a membrane-like environment indicate the presence of a left-handed alpha-helix, probably formed by a sequence of 7 D-amino acids in the peptide. P. tolaasii represents the first reported example of an organism which has evolved the ability to biosynthesize a left-handed alpha-helix. 相似文献
129.
Summary We have recently shown that stimulation of electrogenic HCO
3
–
secretion is accompanied by a simultaneous increase in short-circuit current (I
sc, equivalent to HCO
3
–
secretion rate under these conditions), apical membrane capacitance (C
a
, proportional to membrane area), and apical membrane conductance (G
a
, proportional to membrane ionic permeability). The current experiments were undertaken to explore the ionic basis for the increase inG
a
and the possibility that the rate of electrogenic HCO
3
–
secretion is regulated by changes inG
a
. Membrane electrical parameters were measured using impedance-analysis techniques before and after stimulation of electrogenic HCO
3
–
secretion with cAMP in three solutions which contained different chloride concentrations. In another series of experiments, the effects of an anion channel blocker, anthracene-9-carboxylic acid (9-AA), were measured after stimulation of electrogenic HCO
3
–
secretion with cAMP. The major conclusions are: (i) a measurable apical Cl– conductance exists in control hemibladders; (ii) the transport-associated increase inG
a
includes a Cl–-conductive component; (iii)G
a
also appears to reflect a HCO
3
–
conductance; (iv) the relative magnitudes of the apical membrane conductances to Cl– and HCO
3
–
are similar; (v) 9-AA reducesG
a
andI
sc appear cAMP-stimulated hemibladders; and (vi) alterations inI
sc appear to be mediated by changes inG
a
. 相似文献
130.
R D Woessner M R Mattern C K Mirabelli R K Johnson F H Drake 《Cell growth & differentiation》1991,2(4):209-214
The cellular content of 170kD and 180kD topoisomerase II was studied as a function of the proliferation state and cell cycle position in NIH-3T3 cells. When the cells were synchronized by serum starvation and then stimulated to enter the cell cycle by addition of fresh growth medium, the amount of 170kD topoisomerase II present was undetectable until the cells reached late S phase, peaked in G2-M phase cells, and decreased as the cells completed mitosis. The amount of 180kD topoisomerase II was constant once the cells entered the cell cycle. When exponentially growing cells were induced to enter G0 by serum starvation, the amount of 170kD topoisomerase II decreased in parallel with the loss of cells from the S and G2-M phases of the cell cycle and was undetectable once all of the cells reached G0. In contrast, the 180kD enzyme was still present after all of the cells had entered G0. The tightness of association of the two enzymes with chromatin was measured by determining the concentration of salt required to extract them from isolated nuclei. The 180kD enzyme required a higher concentration of NaCl for extraction than did the 170kD enzyme. The different patterns of expression of the two forms of topoisomerase II suggest that they perform different functions in cells. 相似文献