An antibody and anti-idiotypic antibody against the extra signal peptide of pre-aspartate aminotransferase

A peptide (extra signal peptide) comprising amino acids 1-29 of pig liver pre-mitochondrial aspartate aminotransferase (p-mAAT) was synthesized chemically. The peptide was found to block the import of rat liver p-mAAT into rat liver mitochondria. An antibody raised against the peptide immunoprecipitated rat liver p-mAAT synthesized in a rabbit reticulocyte cell-free translation system. These results suggested that the extra signal peptide sequence of p-mAAT is essential for import of p-mAAT into the mitochondria and that there is structural homology between the extra signal peptides of pig and rat liver p-mAAT. An anti-idiotypic antibody against the peptide was also prepared and purified by affinity chromatography on an Affi-Gel 10 anti-peptide IgG column and was then characterized.     

Cell-free translation of the messenger RNA for calf terminal deoxynucleotidyltransferase

Poly(A)-rich RNA has been isolated from calf thymus and translated in vitro in a rabbit reticulocyte translation system. Three peptides with Mr = 58,000, 33,000, and 13,000 were specifically immunoprecipitated from the translation products with calf terminal deoxynucleotidyltransferase antiserum. An oligo(dT)-purified preparation of calf terminal transferase competed with only the Mr = 58,000 peptide in the immunoprecipitation reaction. The anti-terminal transferase serum did not precipitate a Mr = 58,000 peptide from translation products of spleen or liver mRNA, but it did precipitate the Mr = 33,000 and 13,000 peptides from products of spleen mRNA and a Mr = 13,000 peptide from products of liver mRNA. In addition, when an affinity-purified antibody to calf terminal transferase was used, only a Mr = 58,000 peptide was immunoprecipitated from the translation products of calf thymus mRNA, and none was immunoprecipitated from spleen or liver mRNA products. This antibody also precipitated a Mr = 58,000 peptide from the cell lysates of calf thymocytes labeled in vitro with [35S]methionine. These results demonstrate that calf terminal transferase is biosynthesized as a Mr = 58,000 peptide.     

Peptide mapping by polyacrylamide gel electrophoresis after cleavage at aspartyl-prolyl peptide bonds in sodium dodecyl sulfate-containing buffers

Protein samples prepared for sodium dodecyl sulfate-polyacrylamide gel electrophoresis are preferentially cleaved at aspartyl-prolyl peptide bonds upon heating at 110 degrees C. The presence of aspartyl-prolyl peptide bonds in a protein can therefore be detected by gel electrophoresis of heated samples and the resulting peptides mapped. The method of heat cleavage also works well with proteins in bands cut from electrophoresed gels using modified stacking conditions in the second electrophoresis. An immunoblotting procedure for peptide mapping of nanogram quantities of specific proteins in complex mixtures is demonstrated. Peptide maps produced by aspartyl-prolyl peptide bond cleavage of fructose-1,6-bisphosphatases from different sources show the effectiveness of the above techniques and suggest a conservation of aspartyl-prolyl peptide bonds in pig kidney and mouse and rat liver fructose-1,6-bisphosphatases.     

Structural features of glutamine substrates for human plasma factor XIIIa (activated blood coagulation factor XIII)

The action of human plasma factor XIIIa (thrombin-activated blood coagulation factor XIII) and guinea pig liver transglutaminase on purified caseins, fibrin, the derivatized gamma chain of fibrin, and a number of synthetic glutamine peptides, and peptide derivatives is reported. There are wide variations in the properties of the individual proteins and peptides as substrates for amine incorporation by the two transglutaminases. beta-Casein and several of its derivatives are excellent substrates for factor XIIIa. However, beta-casein is a relatively poor substrate for the liver enzyme. The primary site of amine incorporation by factor XIIIa in beta-casein was identified as glutamine 167. This was accomplished by labeling with fluorescent amine followed by proteolytic digestion and identification of labeled peptides. An 11-residue peptide and a 15-residue peptide, each containing 1 glutamine residue and each modeled after the primary site of amine incorporation in beta-casein, were prepared. A 13-residue peptide modeled after the primary crosslinking site in fibrin gamma chain was also prepared. Each of these polypeptides proved to be an efficient substrate for factor XIIIa and displayed significantly better substrate properties than a number of small glutamine peptide derivatives that are good substrates for liver transglutaminase.     

Phenylalanine hydroxylase-like antibody in human chorionic villi]

An antigen similar by electrophoretic mobility to liver phenylalanine hydroxylase (PH) and cross-reacting with monoclonal antibody PH8 against liver PH was detected in extracts of soluble proteins in 6 from 23 samples of chorionic villi. An antigen with electrophoretic mobility corresponding to 40-41 kDa was detected in extracts of membrane proteins from these 23 samples by immunoblotting with monoclonal antibody PH8. Its molecular weight was similar to that of major chymotryptic peptide of human liver PH. The content of the antigen varied with samples and was less than 20 ng/mg of the extracted protein. Two-dimensional gel electrophoresis revealed only 1 spot of the antigen. The antigen did not react with monoclonal antibodies PH7 and PH9 epitopes of which were located in N-terminal fragment of liver PH. These data suggest that the antigen of membrane fraction could be a PH protein without N-terminal domain.     

Protein and lipid disturbances in rat liver microsomal membranes after bile duct ligation

An analysis of proteins, phospholipids and cholesterol from liver microsomal membranes was performed in normal and post-cholestatic rats. Bile duct ligated rats showed a progressive decrease of these membrane constituents. Minor changes in peptide analysis, a marked decrease of phosphatidylcholine and phosphatidylinositol, disappearance of phosphatidylethanolamine and sphingomyelin, and a clear increment of phosphatidylserine was observed in post-cholestatic as compared to normal group. It was concluded that extra-hepatic cholestasis produces structural changes on the liver microsomes, particularly on phospholipid profile.     

Peptide T from human immunodeficiency virus envelope does not interact with hepatic, intestinal and colonic vasoactive intestinal peptide (VIP) receptors

Acquired immunodeficiency syndrome (AIDS) is initiated by the attachment of the human immunodeficiency virus (HIV) to specific target cells. An octapeptide sequence contained within the envelope of HIV, peptide T, mediates the viral binding. Since there is a considerable structural homology between peptide T and VIP, it has been proposed that the VIP receptor may be the naturally occurring protein which provides the corresponding cellular attachment site. In three different models (rat intestinal epithelial cell membranes, rat liver plasma membranes and human colonic cells), we document the lack of interaction between peptide T and the VIP receptor. These observations would also exclude any pathophysiologic effect caused by the crossreactivity of peptide T or its analogues and these VIP receptors.     

Comparative proteomic analysis of primary mouse liver c-Kit-(CD45/TER119)- stem/progenitor cells

Liver stem/progenitor cells play a key role in liver development and maybe also in liver cancer development. In our previous study a population of c-Kit-(CD45/TER119)- liver stem/progenitor cells in mouse fetal liver, was successfully sorted with large amount (10(6)-10(7)) by using immuno-magnetic microbeads. In this study, the sorted liver stem/progenitor cells were used for proteomic study. Proteins of the sorted liver stem/progenitor cells and unsorted fetal liver cells were investigated using two-dimensional electrophoresis. A two-dimensional proteome map of liver stem/progenitor cells was obtained for the first time. Proteins that exhibited significantly upregulation in liver stem/progenitor cells were identified by peptide mass fingerprinting and peptide sequencing. Nineteen protein spots corresponding to 12 different proteins were identified as showing significant upregulation in liver stem/progenitor cells and seem to play important roles in such cells in cell metabolism, cell cycle regulation, and stress. An interesting finding is that most of the upregulated proteins were overexpressed in various cancers (11 of 12, including 6 in human hepatocellular carcinoma (HCC)) and involved in cancer development as reported in previous studies. Some of the identified proteins were validated by real-time PCR, Western blotting, and immunostaining. Taken together, the data presented provide a significant new protein-level insight into the biology of liver stem/progenitor cells, a key population of cells that might be also involved in liver cancer development.     

Molecular cloning and nucleotide sequence analysis of mRNA for human kidney ornithine aminotransferase. An examination of ornithine aminotransferase isozymes between liver and kidney

The cDNA encoding ornithine aminotransferase (EC 2.6.1.13; OAT) was isolated from a human kidney cDNA library. The isolated cDNA contained the entire protein coding region and partial 3'- and 5'-untranslated regions. The nucleotide sequences of human kidney OAT cDNA were absolutely homologous with those of human liver OAT cDNA, and human kidney and liver OAT fused completely against the antibody to human kidney OAT in an Ouchterlony double diffusion test. These findings settled the controversy as to which characteristics of liver and kidney OAT isozymes are different. An N-terminal sequence analysis of purified mature human kidney OAT clarified that the leader peptide was cleaved between Gln-35 and Gly-36.     

A possible route to the production of free L-tyrosine O-sulphate by the rat

1. l-Tyrosylglycine O[(35)S]-sulphate is metabolized by the rat to yield the O[(35)S]-sulphate esters of l-tyrosine, p-hydroxyphenylpyruvic acid and p-hydroxyphenylacetic acid. 2. The proportion of the administered peptide which is excreted as l-tyrosine O[(35)S]-sulphate is greater at a higher dose. 3. An enzyme capable of hydrolysing the peptide bond of l-tyrosylglycine O[(35)S]-sulphate to yield l-tyrosine O[(35)S]-sulphate has been detected in rat liver and kidney. 4. The activity of this enzyme is completely inhibited by a large excess of l-tyrosylglycine.     

Cloning and expression in Escherichia coli of a rat hepatoma cell cDNA coding for 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase.

In liver, the 470-residue bifunctional enzyme 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase (PFK-2/FBPase-2) catalyses the synthesis and degradation of fructose 2,6-bisphosphate, a potent stimulator of glycolysis. In rat hepatoma (HTC) cells, this enzyme has kinetic, antigenic, and regulatory properties, such as insensitivity to cyclic AMP-dependent protein kinase and lack of associated FBPase-2 activity, that differ from those in liver. To compare the sequence of the HTC enzyme with that of the liver enzyme, we have cloned the corresponding fully-coding cDNA from HTC cells. This cDNA predicts a protein of 448 residues in which the first 32 residues of liver PFK-2/FBPase-2 including the cyclic AMP target sequence have been replaced by a unique N-terminal decapeptide. The rest of the protein is identical with the liver enzyme. An N-terminally truncated recombinant peptide of 380 residues containing the PFK-2 and FBPase-2 domains was expressed in Escherichia coli as a beta-galactosidase fusion protein. It was recognized by anti-PFK-2 antibodies but its enzymic activities were barely detectable. In contrast, a cDNA fully-coding for the HTC enzyme could be expressed in E. coli as a beta-galactosidase-free peptide that exhibited both PFK-2 and FBPase-2 activities. This peptide had those PFK-2 kinetic properties of the HTC enzyme that differ from the liver enzyme. These data, together with immunoblot experiments, suggest that the lack of associated FBPase-2 activity in HTC cells results from a post-translational modification of the enzyme rather than from the difference in amino acid sequence. As well as this peculiar type of PFK-2/FBPase-2 mRNA, HTC cells also contained low concentrations of the liver-type mRNA. Unlike in liver, neither mRNA was induced by dexamethasone in these cells.     

Effect of low doses of the hydra peptide morphogen on protein biosynthesis in the intact and regenerating rat liver

The dependence of ornithine decarboxylase (ODC) activity on hydra peptide morphogen doses has been established. The parameters of protein synthesis were determined in normal and regenerating rat liver, using the peptide in a dose of 20 micrograms/kg body weight, initiating maximum enzyme activity. It was established that intraperitoneal injection of the peptide in partially hepatectomized animals stimulated ODS activity in dose-dependent manner and was dome-shaped. The peptide injection in intact animals does not affect the intensity of 3H-leucine inclusion into the liver protein and the protein content in rat liver. However, the peptide injection in partially hepatectomized animals increased the level of 3H-leucine inclusion into the protein of regenerating liver and stimulated protein accumulation in this type of tissue.     

Sequential activation of MAP kinase activator, MAP kinases, and S6 peptide kinase in intact rat liver following insulin injection.

An insulin-stimulated phosphorylation cascade was examined in rat liver after insulin injection via a portal vein by the use of immune complex kinase assays specific to the mitogen-activated protein (MAP) kinase and S6 kinase II homologue (rsk) kinase. We have prepared an antibody against the peptide consisting of a carboxyl-terminal portion of the extracellular signal-regulated kinase 1 (alpha C92), one of the MAP kinases, and an antibody against the peptide consisting of the carboxyl terminus of the mouse S6 kinase II homologue (alpha rsk(m)C). In alpha C92 immune complex assay, maximal activation of rat liver MAP kinases (approximately 4.3-fold) were observed 4.5 min after insulin injection. We also observed an insulin-stimulated MAP kinase activity (approximately 3-fold) in liver extracts from insulin-treated rat in fractions eluted from phenyl-Sepharose with 30-50% ethylene glycol. Kinase assay in myelin basic protein (MBP)-containing gel after sodium dodecyl sulfate-polyacrylamide gel electrophoresis followed by denaturation with 6 M guanidine HCl, and renaturation revealed that insulin injection stimulated the kinase activity of the 42- and 44-kDa proteins, which corresponded to the two distinct MAP kinases. In alpha rsk(m)C immune complex assay, maximal stimulation (approximately 5-fold) of the S6 peptide (Arg-Arg-Leu-Ser-Ser-Leu-Arg-Ala) kinase activity was observed 7.5 min after insulin injection. In addition, MAP kinases purified from insulin-treated rat liver were able to activate S6 peptide kinase activity in vitro in alpha rsk(m)C immunoprecipitates from untreated rat liver, accompanied by the appearance of several phosphorylated bands including a major band at 88 kDa. We also examined whether insulin injection stimulates the MAP kinase activator (Ahn, N. G., Seger, R., Bratlien, R. L., Diltz, C. D., Tonks, N. K., and Krebs, E. G. (1991) J. Biol. Chem. 266, 4220-4227) in rat liver. Using recombinant Xenopus MAP kinase, fractions of Q-Sepharose eluted early in the NaCl gradient were found to have MAP kinase activator activity accompanied by the phosphorylation of 42-kDa recombinant Xenopus MAP kinase. From these data, we demonstrate three tiers of a cascade composed of the MAP kinase activator, MAP kinases, and an S6 peptide kinase activity in rat liver under physiological conditions in the intact animal.     

Monitor peptide binding sites are expressed in the rat liver and small intestine.

125I-monitor peptide binding was performed using frozen sections of the rat liver and gut and visualized using autoradiography. Saturable binding was observed in unidentified single cells in the liver and in the mucosa of the small intestine. Epidermal growth factor (EGF) and GTPgammaS did not inhibit 125I-monitor peptide binding indicating that the binding sites are not EGF receptors or G protein-coupled receptors. The liver binding site exhibited an affinity 3.7-4.4-fold higher than those in the small intestine. It has been established that intraluminal monitor peptide releases cholecystokinin from the small intestine. The present results indicate that monitor peptide may also have liver associated functions.     

Phosphorylation of rat liver glucocorticoid receptor

Rat liver glucocorticoid-receptor complex (GRc) was purified 2000-fold by a combination of methods including (NH4)2SO4-fractionation and phosphocellulose and DNA-cellulose chromatography. The purified glucocorticoid receptor preparation contained a major peptide of Mr = 90,000 and the GRc sedimented as 4 S in 5-20% sucrose gradients. An additional peptide of Mr = 45,000 (45K) was also observed. Some preparations yielded only the Mr = 90,000 (90K) peptide suggesting that the 45K peptide may be a proteolyzed portion of the 90K protein. The purified GRc was incubated with [gamma-32P]ATP in the presence of cAMP-dependent kinase. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the above preparation revealed the presence of two 32P-containing bands with apparent Mr = 90,000 and 45,000. The 32P incorporation was dependent on the availability of divalent cation (Mg2+). GRc in cytosol labeled with [3H]dexamethasone mesylate and purified as above co-migrated with 32P-containing bands. GRc was also purified from cytosol obtained from livers of rats injected with [32P]orthophosphate. Both 32P and 3H bands were associated with 90K and 45K peptides. Our results indicate that rat liver glucocorticoid receptor is a phosphoprotein and that both the phosphorylated peptides 90K and 45K also contain the steroid and the DNA binding regions of the glucocorticoid receptor.     

海蜇胶原蛋白肽的降血脂及抗氧化作用的研究

本研究以海蜇胶原蛋白为原料,经酶解得到海蜇胶原蛋白肽,探讨海蜇胶原蛋白肽对小鼠血脂的影响及抗氧化作用。以高脂饲料喂养ICR小鼠,建立高脂血症模型,研究胶原蛋白肽对小鼠肝系数和脂肪系数的变化情况及小鼠血脂水平、肝组织抗氧化功能的影响。结果表明海蜇胶原蛋白肽能显著降低小鼠肝系数和脂肪系数,能显著降低高脂血症小鼠血清总胆固醇(TC)、低密度脂蛋白胆固醇(LDL-C)、动脉硬化指数(LDL-C/HDL-C)水平,升高高密度脂蛋白胆固醇(HDL-C)和抗动脉粥样硬化因子(HDL-C/TC);能提高肝组织超氧化物歧化酶(SOD)谷胱甘肽过氧化物酶(GSH-Px)的活力,并能减低丙二醛(MDA)的含量。海蜇胶原蛋白肽具有辅助减低血脂水平和增强抗氧化功能的作用。     

Degradation of heme by a soluble peptide of heme oxygenase obtained from rat liver microsomes by mild trypsinization.

A tryptic peptide of heme oxygenase obtained after solubilization of rat liver microsomes by mild trypsin treatment was purified. The purified peptide gave only a single protein band with a molecular mass of 28 kDa on SDS/PAGE. The tryptic peptide, like the native heme oxygenase, readily bound with substrate heme forming a hemeprotein transiently. The absorption spectra of the ferric, ferrous, ferrous-CO and ferrous-O2 forms of the resulting complex resembled those of the corresponding forms of the complex of heme and the native enzyme. Ferric heme bound to the tryptic peptide was quantitatively decomposed to biliverdin on incubation with a mixture of ascorbic acid and desferrioxamine, indicating that the tryptic peptide still retained catalytic activity. These observations suggest that heme oxygenase has two domains, a hydrophilic and a hydrophobic domain, and that the two domains are folded almost independently of each other. An NADPH-cytochrome-P-450 reductase system composed of NADPH and detergent-solubilized NADPH-cytochrome-P-450 reductase readily reduced the ferric heme bound to the tryptic peptide, but failed to transfer the second electron required for rapid heme degradation, suggesting that the hydrophobic domain of heme oxygenase is important for receiving the second electron from the reductase.     

Liver peptide stabilizing factor protects phosphofructokinase against inactivation by fructose-1,6-bisphosphatase.

Rabbit liver fructose-1,6-bisphosphatase (FDPase) can reversibly inactivate both rabbit muscle and rat liver phosphofructokinases (PFK) under appropriate conditions. The peptide factor which stabilizes rat liver PFK-L₂ against thermal inactivation has now been found to protect both PFKs from inactivation by FDPase. Assay at high ATP (ca. 3 mM) is necessary to demonstrate these reversible changes. In addition, the activation of FDPase by liver cytosol, by oleate plus cytosol, or by oleate plus muscle PFK is lowere about 50% in the presence of peptide factor. These observations suggest an active participation of the peptide factor in regulation of liver glycolysis and gluconeogenesis.     

Preparation of a gap junction fraction from uteri of pregnant rats: the 28-kD polypeptides of uterus, liver, and heart gap junctions are homologous

A procedure for the preparation of a gap junction fraction from the uteri of pregnant rats is described. The uterine gap junctions, when examined by electron microscopy of thin sections and in negatively stained preparations, were similar to gap junctions isolated from heart and liver. Major proteins of similar apparent molecular weight (Mr 28,000) were found in gap junction fractions isolated from the uterus, heart, and liver, and were shown to have highly homologous structures by two-dimensional mapping of their tryptic peptides. An Mr 10,000 polypeptide, previously deduced to be a proteolytic product of the Mr 28,000 polypeptide of rat liver (Nicholson, B. J., L. J. Takemoto, M. W. Hunkapiller, L. E. Hood, and J.-P. Revel, 1983, Cell, 32:967-978), was also studied and shown by chymotryptic mapping to be homologous in the uterine, heart, and liver gap junction fractions. An antibody raised in rabbits to a synthetic peptide corresponding to an amino-terminal sequence of the liver gap junction protein recognized Mr 28,000 proteins in the three tissues studied, showing that the proteins shared common antigenic determinants. These results indicate that gap junctions are biochemically conserved plasma membrane specializations. The view that gap junctions are tissue-specific plasma membrane organelles based on previous comparisons of Mr 26,000-30,000 polypeptides is not sustained by the present results.     

Biological activities of catfish glucagon and glucagon-like peptide

The ability of catfish glucagon and glucagon-like peptide to bind and activate mammalian glucagon receptors was investigated. Neither catfish peptide binds to glucagon receptors of rat liver, hypothalamus or pituitary. Neither stimulates adenylate cyclase activity in liver membranes. Catfish glucagon fails to activate adenylate cyclase in hypothalamic or pituitary membranes in contrast to mammalian glucagon. However, catfish glucagon-like peptide does stimulate hypothalamic and pituitary adenylate cyclase (EC50 approximately 1 pM) possibly through mammalian glucagon-like peptide receptors.