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91.
Selenoproteins are an essential and unique group of proteins in which selenocysteine (Sec) is incorporated in response to a stop codon (UGA). Reprograming of UGA for Sec insertion in eukaryotes requires a cis-acting stem–loop structure in the 3′ untranslated region of selenoprotein mRNA and several trans-acting factors. Together these factors are sufficient for Sec incorporation in vitro, but the process is highly inefficient. An additional challenge is the synthesis of selenoprotein P (SELENOP), which uniquely contains multiple UGA codons. Full-length SELENOP expression requires processive Sec incorporation, the mechanism for which is not understood. In this study, we identify core coding region sequence determinants within the SELENOP mRNA that govern SELENOP synthesis. Using 75Se labeling in cells, we determined that the N-terminal coding sequence (upstream of the second UGA) and C-terminal coding sequence context are two independent determinants for efficient synthesis of full-length SELENOP. In addition, the distance between the first UGA and the consensus signal peptide is also critical for efficiency. 相似文献
92.
Veeranna K. T. Shetty N. Amin P. Grant R. W. Albers H. C. Pant 《Neurochemical research》1996,21(5):629-636
Neuronal cdk5 can phosphorylate certain lys-ser-pro (KSP) motifs of neurofilaments and tau protein in the nervous system.
We have immunoprecipitated the cdk5 from rat brain using a polyclonal antibody raised against the C-terminus of cdk5. The
immunoprecipitate has phosphorylated a KSPXK peptide analog of NF-H, as well as histone H1 and a bacterially expressed rat
NF-H protein. The kinase activity was inhibited by staurosporine, isopentanyladenine and olomoucine in a dose dependent manner.
Kinetic studies indicated Ki values of 39 nM, 38 μM and 8 μM, respectively for staurosporine, isopentanyladenine and olomoucine.
The inhibition by staurosporine was non-competitive with respect to phosphoryl acceptor substrates. Western blot analysis
of the immunoprecipitate showed both cdk5 and p67 (munc-18), a putative regulator molecule of the kinase. Addition of p67
fusion protein enhanced the kinase activity of the immunoprecipitate by 60% above the basal activity. P67 elevated Ki values
for both staurosporine and olomoucine. The degree of inhibition at high concentrations of these inhibitors was unaltered by
exogenous p67 indicating a lack of competitive interactions with p67. The high affinity of staurosporine for cdk5 suggests
that cdk5 may be one of the targets for the neurotropic effect of staurosporine. 相似文献
93.
P. Shetty 《Applied Biochemistry and Microbiology》2016,52(2):176-182
The extracellular amylolytic activity elaborated by the nematophagous fungus Arthrobotrys conoides was found to resolve into 2 amylolytic peaks when fractionated on Sephadex G-100 column. Around 80% of the eluted glucoamylase activity was attributed to peak I (GA A). GA A being cationic in nature was purified about 70-fold with 57% yield by negative chromatography on DEAE Sephadex at pH 7.0. The enzyme was stable over a broad pH range of 4.8–9.0. KM for the linear polysaccharide amylose was 0.34 mg/mL. Enzyme showed high affinity for the branched polysaccharides as the KM values for amylopectin, glycogen and starch were 0.056, 0.062 and 0.065 mg/mL, respectively. The enzyme clearly demonstrated raw starch digestibility. Probable involvement of Trp and His residues in enzyme catalysis was elucidated using group-specific reagents. 相似文献
94.
95.
Studies on groundnut proteins. III. Physicochemical properties of arachin prepared by different methods 总被引:1,自引:0,他引:1
The homogeneity of arachin prepared by different methods was determined by the techniques of polyacrylamide gel electrophoresis, DEAE-cellulose chromatography, and ultracentrifugation. Arachin obtained by the method of Tombs (Biochem. J.96, 119, 1965) or Dawson (Anal. Biochem.41, 305, 1971) appeared to be homogeneous by these techniques. Total groundnut proteins, extracted in 1 m NaBr solution and subjected to double precipitation with 23% (NH4)2SO4, also gave a homogeneous arachin preparation. These three homogeneous arachin preparations differed in their rate of hydrolysis by alpha-chymotrypsin, heat coagulation, and dissociation into subunits. However, SDS1 and GuHCl denatured them to the same extent, as could be judged by the difference spectra. The phosphorus and carbohydrate content of the three preparations did not differ significantly. 相似文献
96.
A rapid method for the isolation of ribonuclease from yeast (Saccharomyces carlsbergensis). 总被引:1,自引:0,他引:1
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A ribonuclease (RNAase; EC 3.1.14.1) from brewer's yeast was purified 90-fold. Crude RNAase was initially separated from other proteins by precipitation at pH 4.0 after incubation of the mechanically disrupted yeast cells at pH 6.0 and 52 degrees C for 30 min. The RNAase was purified from the supernatant by ultrafiltration with a PM-30 membrane and adsorption chromatography on hydroxyapatite. RNAase preparation was free of phosphatase, deoxyribonuclease and phosphodiesterase activities. It showed maximum activity at pH 6.0 and a temperature optimum of 52 degrees C with yeast RNA as substrate. This RNAase hydrolysed yeast RNA to nucleoside 3'-phosphates and showed no evidence of base specificity. 相似文献
97.
The homogeneity of a purified ribonuclease from brewers' yeast was determined by velocity sedimentation and polyacrylamide gel electrophoresis techniques. The velocity sedimentation pattern gave a single peak with a Sapp 3.46 and polyacrylamide gel electrophoresis showed one major band. The absorption spectrum of the enzyme showed maximum absorption at 277–278 nm and minimum at 252 nm. The enzyme was relatively stable to extreme pH values and high temperature. Both NaCl and KCl increased the enzyme activity whereas enzyme was inhibited by divalent metal ions. The inhibition of the enzyme was increased in the order of Ca2+ > Mg2+ > Fe2+Cu2+. Chemical modification studies of the enzyme showed that tryptophan residues and disulfide bonds were required for enzyme activity. 相似文献
98.
Morphine and several other opioid agonists including the enkephalins caused a dual action on the twitch in the isolated, curarized, and electrically stimulated frog toe muscle; a potentiating action at low drug concentrations and a potentiation followed by an inhibitory action at higher concentrations. The twitch potentiation was found to be nonstereospecific and resistant to antagonism by naloxone. The inhibitory action too was naloxone-resistant and is probably due to a nonspecific local anesthetic effect of the opioids on the electric properties of the frog skeletal muscle fibre membrane. 相似文献
99.
100.