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排序方式: 共有152条查询结果,搜索用时 15 毫秒
1.
A Del Corso D Barsacchi M Camici D Garland U Mura 《Archives of biochemistry and biophysics》1989,270(2):604-610
Two structurally different forms of bovine lens aldose reductase have been identified. Freshly prepared lens extracts contain an unactivated "b form" (ARb) which is sensitive to inhibition by Sorbinil. Upon incubation of the extracts with oxygen radical generating systems, ARb is converted to a more active "a form" (ARa), which is not inhibited by Sorbinil. ARa and ARb were purified to electrophoretic homogeneity. 相似文献
2.
Giampaolo Manao Luigia Pazzagli Paolo Cirri Anna Caselli Guido Camici Gianni Cappugi Ahmad Saeed Giampietro Ramponi 《Journal of Protein Chemistry》1992,11(3):333-345
Two lowM
r phosphotyrosine protein phosphatases have been isolated from rat liver. The enzymes were previously known as lowM
r acid phosphatases, but several recent studies have demonstrated that this family of enzymes possesses specific phosphotyrosine protein phosphatase activity. We determined the complete amino acid sequences of the two isoenzymes and named them AcP1 and AcP2. Both consist of 157 amino acid residues, are acetylated at the NH2-terminus, and have His as the COOH-terminus. The molecular weights calculated from the sequences are 18,062 for AcP1 and 17,848 for AcP2. They are homologous except in the 40–73 zone, where about 50% of residues are different. This fact suggests that the two isoenzymes are produced by an alternative splicing mechanism. There is no homology between these two isoenzymes and the receptor-like phosphotyrosine protein phosphatases LAR, CD45, human placenta PTPase 1B, and rat brain PTPase-1. AcP1 and AcP2 are also distinct from rat liver PTPase-1 and PTPase-2, since these last enzymes have higher molecular weights. AcP1 differs from AcP2 with respect to (1) substrate affinity and (2) its sensitivity to activators and inhibitors, thus suggesting a their different physiological function. 相似文献
3.
Y Wang M Camici F T Lee Z Ahmad A A DePaoli-Roach P J Roach 《Biochimica et biophysica acta》1986,888(2):225-236
Rat liver glycogen synthase was purified to homogeneity by an improved procedure that yielded enzyme almost exclusively as a polypeptide of Mr 85,000. The phosphorylation of this enzyme by eight protein kinases was analyzed by cleavage of the enzyme subunit followed by mapping of the phosphopeptides using polyacrylamide gel electrophoresis in the presence of SDS, reverse-phase high-performance liquid chromatography and thin-layer electrophoresis. Cyclic AMP-dependent protein kinase, phosphorylase kinase, protein kinase C and the calmodulin-dependent protein kinase all phosphorylated the same small peptide (approx. 20 amino acids) located in a 14 kDa CNBr-fragment (CB-1). Calmodulin-dependent protein kinase and protein kinase C also modified second sites in CB-1. A larger CNBr-fragment (CB-2) of approx. 28 kDa was the dominant site of action for casein kinases I and II, FA/GSK-3 and the heparin-activated protein kinase. The sites modified were all localized in a 14 kDa species generated by trypsin digestion. Further proteolysis with V8 proteinase indicated that FA/GSK-3 and the heparin-activated enzyme recognized the same smaller peptide within CB-2, which may also be phosphorylated by casein kinase 1. Casein kinase 1 also modified a distinct peptide, as did casein kinase II. The results lead us to suggest homology to the muscle enzyme with regard to CB-1 phosphorylation and the region recognized by FA/GSK-3, which in rabbit muscle is characterized by a high density of proline and serine residues. A striking difference with the muscle isozyme is the apparent lack of phosphorylations corresponding to the muscle sites 1a and 1b. These results provide further evidence for the presence of liver- and muscle-specific glycogen synthase isozymes in the rat. That the isozymes differ subtly as to phosphorylation sites may provide a clue to the functional differences between the isozymes. 相似文献
4.
C Fini M Camici A Minelli A Floridi P L Ipata 《The International journal of biochemistry》1986,18(8):683-689
Both purified and membrane-bound 5'-nucleotidases (EC 3.1,3.5) from guinea pig skeletal muscle and bull seminal plasma are inhibited by Concanavalin A (Con A). 5'-Nucleotidase purified from skeletal muscle is inhibited by Con A by an apparent uncompetitive process (K'i = 160 nM), while the lectin inhibits the particulate enzyme by an apparent non-competitive process (Ki = K'i = 50 nM). 5'-Nucleotidase purified from bull seminal plasma is inhibited by Con A by an apparent non-competitive process (K'i = Ki = 270 nM), while the membrane-bound enzyme is subjected to a mixed type inhibition by the lectin (K'i greater than Ki; 30 and 14 nM, respectively). The enzyme purified from skeletal muscle exhibits a significant cooperativity in the interaction with Con A. The inhibition of bull seminal plasma particulate 5'-nucleotidase brought about by Con A is not completely reversed by addition of alpha-methyl-D-mannoside. 相似文献
5.
G Camici G Manao M Stefani A Berti G Cappugi G Liguri G Ramponi 《The Italian journal of biochemistry》1984,33(1):1-16
Turkey muscle acylphosphatase is strongly bound to anti-(horse muscle acylphosphatase ) antibodies covalently linked to an agarose resin. This permits use of an affinity chromatography step in the purification, which increased the final yield and allowed us to isolate three different molecular forms of the enzyme. Form 1 is a mixed disulfide between the polypeptide chain and glutathione; form 3 is an S-S dimer of the polypeptide chain present in form 1, while form 2, present in a very low amount, consists of a polypeptide chain quite similar in aminoacid composition to that found in form 1. The three molecular forms show very similar kinetic parameters. The comparison of these molecular forms with those isolated from horse muscle showed similar kinetic properties but different structural features. 相似文献
6.
A Del Corso D Barsacchi M Giannessi M G Tozzi M Camici U Mura 《The Journal of biological chemistry》1989,264(30):17653-17655
Bovine lens aldose reductase (alditol:NADP+ oxidoreductase, EC 1.1.1.21) undergoes an oxidative modification, greatly stimulated by high ionic strength, upon incubation in the presence of oxygen radical generating systems (Del Corso, A., Camici, M., and Mura, U. (1987) Biochem. Biophys. Res. Commun. 148, 369-375). The enzyme modification is accompanied by a change in stereospecificity toward the two enantiomers of glyceraldehyde. In particular, the Km for L-glyceraldehyde of the native form increased over 150 times after the enzyme modification, with a decrease in the catalytic efficiency of over 200 times. By contrast, for the D-enantiomer the Km increased only 7 times with respect to the native form, with a concomitant decrease in the catalytic efficiency of only approximately 3 times. This dramatic change in stereospecificity may account for the reported apparent cooperative behavior exhibited also by highly purified electrophoretically homogeneous preparations of aldose reductase. 相似文献
7.
Mitochondria can synthesize phosphatidyl-ethanolamine (PE) through phosphatidylserine decarboxylase (PS decarboxylase) activity or can import this lipid from the endoplasmic reticulum. In this work, we studied the factors influencing the import of PE in brain mitochondria and its utilization for the assembly of mitochondrial membranes. Incubation of rat brain homogenate with [1-3H]ethanolamine resulted in the synthesis and distribution of 3H-PE to subcellular fractions. T-wenty-one percent of labeled PE was recovered in purified mitochondria. The import of PE in mitochondria was studied in a reconstituted system made of microsomes (donor particles) and purified mitochondria (acceptor particles). Ca+2 and nonspecific lipid transfer protein purified from liver tissue (nsL-TP) enhanced the translocation process. 3H-PE synthesized in membrane associated to mitochondria (MAM) could also translocate to mitochondria in the reconstituted system. Exposure of mitochondria to trinitrobenzensulfonic acid (TNBS) resulted in the reaction of more than 60% of 3H-PE imported from endoplasmic reticulum and of about 25% of 14C-PE produced in mitochondria by decarboxylation of 14C-PS. Moreover, the removal of the outer mitochondrial membrane by digitonin treatment, resulted in the loss of 3H-PE, but not 14C-PE. These results indicate that labeled PE imported in mitochondria is mainly localized in the outer mitochondrial membrane, whereas PE produced by PS decarboxylase activity is confined to the inner mitochondrial membrane. Phospholipase C hydrolyzed 25–30% of both PE radioactivity and mass of the outer mitochondrial membrane indicating an asymmetrical distribution of this lipid across the membrane.Mr. Carlo Ricci is thanked for his skillful technical assistance. This work has been supported by a grant from the Ministry of Education, Rome, Italy. 相似文献
8.
F. Fallarino †A. A. Genazzani S. Silla †M. R. L'Episcopo ‡O. Camici ‡L. Corazzi †F. Nicoletti M. C. Fioretti 《Journal of neurochemistry》1995,65(2):912-918
Abstract: [3H]Aniracetam bound to specific and saturable recognition sites in membranes prepared from discrete regions of rat brain. In crude membrane preparation from rat cerebral cortex, specific binding was Na+ independent, was still largely detectable at low temperature (4°C), and underwent rapid dissociation. Scatchard analysis of [3H]aniracetam binding revealed a single population of sites with an apparent KD value of ~70 nM and a maximal density of 3.5 pmol/mg of protein. Specifically bound [3H]aniracetam was not displaced by various metabolites of aniracetam, nor by other pyrrolidinone-containing nootropic drugs such as piracetam or oxiracetam. Subcellular distribution studies showed that a high percentage of specific [3H]aniracetam binding was present in purified synaptosomes or mitochondria, whereas specific binding was low in the myelin fraction. The possibility that at least some [3H]aniracetam binding sites are associated with glutamate receptors is supported by the evidence that specific binding was abolished when membranes were preincubated at 37°C under fast shaking (a procedure that substantially reduced the amount of glutamate trapped in the membranes) and could be restored after addition of either glutamate or α-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) but not kainate. The action of AMPA was antagonized by DNQX, which also reduced specific [3H]aniracetam binding in unwashed membranes. High levels of [3H]aniracetam binding were detected in hippocampal, cortical, or cerebellar membranes, which contain a high density of excitatory amino acid receptors. Although synaptosomal aniracetam binding sites may well be associated with AMPA-sensitive glutamate receptors, specifically bound [3H]aniracetam could not be displaced by cyclothiazide or GYKI 52466, which act as a positive and negative modulator of AMPA receptors, respectively. 相似文献
9.
C Ciudad M Camici Z Ahmad Y Wang A A DePaoli-Roach P J Roach 《European journal of biochemistry》1984,142(3):511-520
Isolated rat hepatocytes were incubated in a medium containing 0.1 mM [32P]phosphate (0.1 mCi/ml) before exposure to epinephrine, glucagon or vasopressin. 32P-labeled glycogen synthase was purified from extracts of control or hormone-treated cells by the use of specific antibodies raised to rabbit skeletal muscle glycogen synthase. Analysis of the immunoprecipitates by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate indicated that a single 32P-labeled polypeptide, apparent Mr 88000, was removed specifically by the antibodies and corresponded to glycogen synthase. Similar electrophoretic analysis of CNBr fragments prepared from the immunoprecipitate revealed that 32P was distributed between two fragments, of apparent Mr 14000 (CB-1) and 28000 (CB-2). Epinephrine, vasopressin or glucagon increased the 32P content of the glycogen synthase subunit. CB-2 phosphorylation was increased by all three hormones while CB-1 was most affected by epinephrine and vasopressin. These effects correlated with a decrease in glycogen synthase activity. From studies using rat liver glycogen synthase, purified by conventional methods and phosphorylated in vitro by individual protein kinases, it was found that electrophoretically similar CNBr fragments could be obtained. However, neither cyclic-AMP-dependent protein kinase nor three different Ca2+-dependent enzymes (phosphorylase kinase, calmodulin-dependent protein kinase, and protein kinase C) were effective in phosphorylating CB-2. The protein kinases most effective towards CB-2 were the Ca2+ and cyclic-nucleotide-independent enzymes casein kinase II (PC0.7) and FA/GSK-3. The results demonstrate that rat liver glycogen synthase undergoes multiple phosphorylation in whole cells and that stimulation of cells by glycogenolytic hormones can modify the phosphorylation of at least two distinct sites in the enzyme. The specificity of the hormones, however, cannot be explained simply by the direct action of any known protein kinase dependent on cyclic nucleotide or Ca2+. Therefore, either control of other protein kinases, such as FA/GSK-3, is involved or phosphatase activity is regulated, or both. 相似文献
10.
Deoxyribose 5-phosphate aldolase was purified 41 times from Bacillus cereus induced by growth on deoxyribonucleosides. The purification procedure includes ammonium sulphate fractionation, gel filtration on Sephadex G-100, ion-exchange chromatography on DEAE-Sephacel and preparative electrophoresis on 10% polyacrylamide gel. The enzyme is stable above pH 6.5, but is rapidly inactivated by sulfhydryl reagents. Being insensitive to EDTA, it may be considered as a Class I aldolase. Among a number of compounds tested (including some carboxylic acids, free and phosphorylated pentoses, nucleotides and nucleosides), none has been found to affect the enzyme activity. The enzyme appears to be dimeric, with a subunit Mr of 23,600. A Km of 4.4 x 10(-4) M was calculated for dRib 5-P. 相似文献