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101.
Gianfranco Di Matteo Giovanni Romeo Guido Di Prisco 《Archives of biochemistry and biophysics》1980,200(1):55-60
A study on the response of the stability and activity of crystalline ox liver nuclear and mitochondrial glutamate dehydrogenases to temperature variations has been carried out. The thermodynamic properties of the heat inactivation process and of the reaction with the substrates glutamate and α-ketoglutarate have been investigated. The heat inactivation of nuclear glutamate dehydrogenase proceeds at a faster rate than that of the mitochondrial enzyme in the temperature range 40–51 °C; the enthalpy of activation of the inactivation process is higher and the entropy is almost double, compared to the values of mitochondrial glutamate dehydrogenase. The effect of temperature on the maximal velocity shows that, with both glutamate and α-ketoglutarate, the enthalpy of activation with nuclear glutamate dehydrogenase is double and the decrease in entropy almost half of the values of the mitochondrial enzyme. The variation of the apparent Km with temperature shows a decrease of the affinity of both enzymes for glutamate, with no major difference in the thermodynamic properties of the reaction. With α-ketoglutarate, on the other hand, the affinity of nuclear glutamate dehydrogenase decreased, whereas that of the mitochondrial enzyme increased with temperature. The process is therefore exothermic with the former enzyme, endothermic with the latter; furthermore, it occurs with a decrease in enthropy with nuclear glutamate dehydrogenase, but with a large increase with the mitochondrial enzyme. The studies on the effect of temperature on the activity were carried out in the range 20–44 °C. 相似文献
102.
A method of monitoring slow rotational motions of proteins from the decay of the intrinsic phosphorescence is described. The phosphorescence is excited with a 10-μsec pulse of vertically polarized light from an air gap lamp, and the anisotropy was computed as a function of time from the simultaneously detected vertically and horizontally polarized components of the emission. The approach is illustrated with time-dependent measurements of the anisotropy of the tryptophan phosphorescence of Staphylococcus aureus nuclease, bovine carbonic anhydrase, and liver alcohol dehydrogenase in glycerol-phosphate buffer between ?90 and ?70°C. The temperature- and molecular-weight dependence of the exponential decays in the anisotropy indicate that overall rotation of the proteins is at the origin of the depolarization. The potential of the approach as a probe of the slow rotational motions of proteins in membranes and other macromolecular complexes is stressed. 相似文献
103.
Nanni P Nicoletti G De Giovanni C Galli MC 《Bollettino della Società italiana di biologia sperimentale》1979,55(2):113-116
Cytoplasmic receptors for 5 alpha-dihydrotestosterone (3H-DHT) were determined in normal and hypertrophic human prostate using the slightly modified DCC method we previously standardized for 17beta-estradiol-receptor. Incubations were always performed at 0 degree C for 1 hr. Discrimination between 3H-DHT binding to cytoplasmic receptor and to Sex Hormone Binding Globulin (SHBG) was achieved on the basis of binding affinity, thermolability and pattern of specificity by various steroid hormones. In particular, 5 beta-DHT did not bind to cytoplasmic receptor, while it did to SHBG. 相似文献
104.
De Giovanni C Nicoletti G Galli MC Nanni P 《Bollettino della Società italiana di biologia sperimentale》1979,55(2):117-121
A method for determining cytoplasmic progesterone receptor was standardized in normal human endometrium comparing two different tracers, 3H-progesterone (3H-P) and 3H-medroxyprogesterone acetate (3H-MAP), a synthetic progestin which does not bind to Corticosteroid Binding Globulin (CBG). Receptor assays were performed as previously reported for 17beta-estradiol receptor, with slight modifications: incubation lasted 1 hr at 0 degree C, followed by 5 min DCC exposure under the same conditions. When 3H-P was employed as tracer, blanks performed with cold MAP gave similar results as using cortisol in incubation tubes and progesterone and cortisol in blanks. 3H-MAP was a good tracer for progesterone receptor because it neither bound to CBG nor to androgen or cortisol receptors; it had very high affinity and specificity for P-R; it was not metabolized by cytosol at 0 degree C and, finally, it detected receptor amounts quite comparable to those obtained using 3H-P. 相似文献
105.
Pasquale Petrilli Pietro Pucci Anna Maria Garzillo Giovanni Sannia Dr. Gennaro Marino 《Molecular and cellular biochemistry》1981,35(2):121-128
Summary Reactivity of sulphydryl groups of cytosolic and mitochondrial aspartate aminotransferases from ox heart has been studied.
A total of 5 and 7 cysteine residues per monomer are present in cAATo and mAATo, respectively. In native conditions only a
single sulphydryl group can be titrated by Nbs2 while the catalytic activity remains unchanged, however in the mitochondrial isozyme the reactivity depends on the functional
state of the enzyme. Reactivity toward NEM reveals the existence of a syncatalytic sulphydryl group in the cytosolic isozyme.
Titration of cAATo with pMB at pH 8 and pH 5 confirms the existence of two exposed sulphydryl groups with a different reactivity.
The results compared with those reported on the corresponding isozymes from pig and chicken heart show that syncatalytic sulphydryl
groups are of general occurrence in these enzymes. 相似文献
106.
Giovanni Felice Azzone Stefano Massari Tullio Pozzan 《Molecular and cellular biochemistry》1977,17(2):101-112
Summary The evidence that all energy transducing membranes can generate a proton electrochemical potential difference,
H, across the membrane and that this potential can be used to transfer energy among energy transducing units and to generate ATP, has increased the interest for the view that
H plays an obligatory role in energy transduction and ATP synthesis. In the present article we shall concentrate on two experimental questions related with the generation and role of
H: (a) the charge/site ratio; (b) the relation between the proton electrochemical potential on one side and the cation electrochemical potential, the phosphate potential and the redox potential on the other. We shall then discuss the view that energy transduction corresponds to a molecular energy machine rather than to a fuel cell. 相似文献
107.
Giovanni Romeo 《Human genetics》1977,39(3):261-276
Summary In four of the five autosomal dominant porphyrias four different partial enzymatic defects of the porphyrin biosynthetic pathway have been discovered in the last few years. With the exception of protoporphyria, the residual enzymatic activity in carriers of these defects is approximately equal to 50% of that found in controls. In each case the pattern of excretion of porphyrin and/or porphyrin precursors reflects the site of the partial metabolic block. There are indications, at least in intermittent acute porphyria, that the degree of penetrance of the disorder varies according to the level of phenotypic expression, being highest for the enzyme deficiency, lower for the excretion of precursors and lowest for the clinical symptoms. It is proposed that environmental factors, and probably also gene interaction, are the cause of the different degrees of penetrance.On leave from the University of Naples, Italy 相似文献
108.
109.
Serotonin (5HT) containing 180 instead of 160 was found in brain after exposing rats to an atmosphere of 1802. The 180 incorporation appeared linear with time and 22% of the 5HT in striatum contained 180 after one hour of exposure. 180 entered 5HT by enzymatic reaction rather than by isotope exchange as treatment with p-chlorophenylalanine, to block tryptophan hydroxylase, prevented incorporation, while more 180-5HT than normal was found in brain after treatment with pargyline, to block monoamine oxidase. Our studies suggest that the incorporation of 1802 into brain 5HT might be a feasible approach for evaluating 5HT turnover in animals and with some modification might be applied in man. 相似文献
110.
An improved approach for transformation of plant cells by microinjection: molecular and genetic analysis 总被引:4,自引:0,他引:4
Martin Schnorf Gabriele Neuhaus-Url Alessandro Galli Shigeru Iida Ingo Potrykus Gunther Neuhaus 《Transgenic research》1991,1(1):23-30
A new culture method for the injection of tobacco mesophyll protoplasts has been established. The protoplasts are embedded
in a thin layer of alginate and are nourished from the medium in the underlying basislayer. In the alginate layer the protoplasts
regenerate to calli at a frequency of up to 80%. Embedded protoplasts can be selected either with 50 mg l−1 kanamycin or 5 mg l−1 paromomycin. Single resistant cells can be recovered from about 10 000 sensitive cells in one alginate layer. Injection of
theneo gene (coding for neomycin phosphotransferase II) into protoplast derived single cells in the alginate layer results in kanamycin
resistant colonies that can be regenerated to mature plants. These plants express the neomycin phosphotransferase as shown
by enzyme activity assay. The integration of the transgene into the plant genome could be proved by Southern hybridization
to high molecular weight DNA. With this culture method 100 cells can be injected per hour. Transformation frequencies range
from 2 to 20%. In crossing experiments, it was shown that the foreign gene is transmitted to the next generation in a Mendelian
fashion. 相似文献