Fluorescence spectroscopic study of the interaction of saporin with phospholipid vesicles

Saporin-S6 (SO-6) is a type-1 ribosome-inactivating protein purified from the seeds of Saponaria officinalis. The fluorescence characteristics of SO-6 were studied in the presence and absence of phospholipids. The interaction of SO-6 with DMPG or DMPC vesicles results in a decrease in the fluorescence emission intensity of tryptophan without any shift in the emission maximal wavelength. The results of fluorescence titration indicate that DMPG/SO-6 saturation molar ratio is 100: 1, but the binding of DMPC with SO-6 does not reach a saturating plot. A shielding of the tryptophan fluorescence from quenching by acrylamide on interaction with the phospholipids was observed, and this shielding was more pronounced in the presence of DMPG. The interaction of SO-6 with DMPG vesicles is stronger in the liquid-crystalline phase than in the gel phase. Extrinsic fluorescence studies indicated that the interaction of the protein with DMPG vesicles does not modify the phase transition temperature of the lipid, but decreases the amplitude of the change of fluorescence anisotropy associated with the co-operative melting of 1,6-diphenyl-1,3,5-hexatriene (DPH)-labelled vesicles. These results indicate that both electrostatic and hydrophobic components are involved in the SO-6-lipid vesicle interaction.

[The value of urine cystein proteinase and serum CA125 measurement in monitoring the treatment of malignant ovarian tumor]

Urine cystein proteinase (UCP) and serum CA125 were measured in 40 patients with malignant ovarian tumor (malignant group), 40 patients with benign ovarian tumor (benign group), and 40 normal control (normal group). 28 patients in the malignant group underwent UCP and CA125 measurement pre-operation, post-operation, and during three courses of chemotherapy. The enzyme activity of UCP in the malignant group was significantly higher than that in the benign and normal groups (P < 0.05 or 0.01). The values of UCP in patients with malignant tumor of stages II-IV were significantly higher compared with those of stages I-II (P < 0.01, 0.05). The activity of UCP was elevated pre-operation, post-operation, and was much higher on the seventh day postoperation. After the seventh day, UCP activity decreased gradually. Serum CA125 was also detected pre-operation, at 7.30 and 60 days post-operation. The levels of UCP and CA125 pre-operation and 30, 60 days post-operation in the patients whose residual carcinoma lesions were > 2 cm in diameter were apparantly higher than those with no residual lesions (P < 0.05). UCP and CA125 values were measured in six patients before relaparotomy. The sensitivity, specificity, accuaracy, positive predictive value and negative predictive value for UCP assay are 980%, 100%, 83%, 100% and 50% and those for CA125 assay are 40%, 100%, 80%, 100%, and 25%, respectively.

Regulation of 5'-AMP-activated protein kinase activity by the noncatalytic beta and gamma subunits

The mammalian 5'-AMP-activated protein kinase is a heterotrimer consisting of an alpha catalytic subunit and beta and gamma noncatalytic subunits, each of which is represented in a larger isoprotein family, related to the SNF1 kinase and its interacting proteins in yeast. In this study, we have used mammalian cell transfection to compare the activities of the two alpha subunit isoforms, alpha-1 and alpha-2, and to study the influence of the noncatalytic subunits on enzyme subunit association and activity. Expression of epitope-tagged protein subunits in COS7 cells indicates detectable but low level kinase activity for each of the two catalytic alpha subunits. Co-expression of alpha subunits with the beta or gamma subunits modestly increases kinase activity accompanied by the formation of alpha/beta or alpha/gamma heterodimers. Co-expression of all three subunits, however, is accompanied by a 50-110-fold increase in kinase activity with the formation of a heterotrimeric complex. In addition to binding of each noncatalytic subunit to the alpha subunit, the beta and gamma subunits bind to each other, likely resulting in a more stable heterotrimeric complex. The increase in kinase activity associated with expression of this heterotrimer is due both to an increase in enzyme-specific activity (units/enzyme mass) and to an apparent enhanced alpha subunit expression. Co-expression of a catalytically defective alpha subunit or the beta/gamma-binding COOH-terminal domain of the alpha subunit results in reduced heterotrimeric kinase activity. The synergistic positive regulatory roles for both the noncatalytic beta and gamma subunits of 5'-AMP-activated protein kinase contrasts with the Snf1p kinase, where only heterodimers of Snf1p and Snf4p seem to be required for maximum kinase activity.

Receptor specificity of the fibroblast growth factor family

Fibroblast growth factors (FGFs) are essential molecules for mammalian development. The nine known FGF ligands and the four signaling FGF receptors (and their alternatively spliced variants) are expressed in specific spatial and temporal patterns. The activity of this signaling pathway is regulated by ligand binding specificity, heparan sulfate proteoglycans, and the differential signaling capacity of individual FGF receptors. To determine potentially relevant ligand-receptor pairs we have engineered mitogenically responsive cell lines expressing the major splice variants of all the known FGF receptors. We have assayed the mitogenic activity of the nine known FGF ligands on these cell lines. These studies demonstrate that FGF 1 is the only FGF that can activate all FGF receptor splice variants. Using FGF 1 as an internal standard we have determined the relative activity of all the other members of the FGF family. These data should serve as a biochemical foundation for determining developmental, physiological, and pathophysiological processes that involve FGF signaling pathways.

Non-catalytic beta- and gamma-subunit isoforms of the 5'-AMP-activated protein kinase

The mammalian 5'-AMP-activated protein kinase (AMPK) is a heterotrimeric protein consisting of alpha-, beta-, and gamma-subunits. The alpha-subunit is the catalytic subunit and is related to the yeast Snf1p kinase. In this study, we report the cloning of full-length cDNAs for the non-catalytic beta- and gamma-subunits. The rat liver AMPK beta-subunit clone predicts a protein of 30,464 Da, which is related to the Sip1p, Sip2p, and Gal83p subfamily of yeast proteins that interact with Snf1p and are involved in glucose regulation of gene expression. The AMPK beta-subunit, when expressed in bacteria and in mammalian cells, migrates anomalously on SDS gels at an apparent molecular mass of 40 kDa. Rat and human liver AMPK gamma-subunit clones predict a protein of 37,577 Da (AMPK-gamma1), which is related to the yeast Snf4p protein that copurifies with Snf1p and to a larger family of other human AMPK gamma-isoforms. The mRNAs for both AMPK- beta and AMPK-gamma1 are widely expressed in rat tissues, consistent with a broad role for AMPK in cellular regulation. These data reveal a mammalian multisubunit protein kinase strikingly similar to the multisubunit glucose-sensing Snf1 kinase complex. The identification of isoform families for the AMPK subunits indicates the potential diversity of the roles of this highly conserved signaling system in nutrient regulation and utilization in mammalian cells.

Aggregation of phospholipid vesicles induced by the ribosome inactivating protein saporin

Saporin-S6(SO-6) is a single chain ribosome inactivating protein, which can inhibit protein synthesis by inactivating eukaryotic ribosomes. The interaction of SO-6 with phospholipid model systems was described. SO-6 can specifically interact with negatively-charged phospholipid vesicles and it induces the aggregation of the lipid vesicles. The kinetics of the vesicle aggregation induced by SO-6 was studied. The saturating protein/lipid molar ratio was determined to be 1:100 based on titration experiments. The aggregation is dependent on the temperature in a range that was many times higher than the phase transition temperature of the phospholipid. The effect of pH on the aggregation of the vesicles can not be explained by simple deprotonation of side chain amino groups of the protein, and may be related to conformational changes of the protein. The maintenance of physiological ionic strength was required for the aggregation of SO-6 with vesicles. Finally, the interaction was prompted by Ca2+ ions, and was totally inhibited by EDTA, which suggests that SO-6 may interact with phospholipid vesicles in a Ca(2+)-dependent manner.

Mammalian AMP-activated protein kinase subfamily

The mammalian 5'-AMP-activated protein kinase (AMPK) is related to a growing family of protein kinases in yeast and plants that are regulated by nutritional stress. We find the most prominent expressed form of the hepatic AMPK catalytic subunit (alpha 1) is distinct from the previously cloned kinase subunit (alpha 2). The alpha 1 (548 residues) and alpha 2 (552 residues) isoforms have 90% amino acid sequence identity within the catalytic core but only 61% identity elsewhere. The tissue distribution of the AMPK activity most closely parallels the low abundance 6-kilobase alpha 1 mRNA distribution and the alpha 1 immunoreactivity rather than alpha 2, with substantial amounts in kidney, liver, lung, heart, and brain. Both alpha 1 and alpha 2 isoforms are stimulated by AMP and contain noncatalytic beta and gamma subunits. The liver alpha 1 isoform accounts for approximately 94% of the enzyme activity measured using the SAMS peptide substrate. The tissue distribution of the alpha 2 immunoreactivity parallels the alpha 2 8.5-kilobase mRNA and is most prominent in skeletal muscle, heart, and liver. Isoforms of the beta and gamma subunits present in the human genome sequence reveal that the AMPK consists of a family of isoenzymes.

Four outbreaks of human trichinellosis in Henan Province

Four outbreaks of human trichinellosis caused by eating pork together had occurred successively in two rural areas and two cities of Henan Province, where the disease is endemic. Of the 110 persons involved, 54 had the onset. All of them had the history of eating pork. In the outbreak of Dengzhou, in those persons who dined together, men were all uninfected and 13 women were infected. The difference found between sexes was suggested to be related with spirit drinking. In these 54 patients, the latent period ranged from 3 to 28 days. The relevant clinical symptoms and signs were fever, edema, myalgia, rash, headache, nausea, abdominal pain and diarrhea. Vomiting was uncommon. Most patients were hospitalized and all cases recovered in two weeks after proper treatment with albendazole.

[Analysis of total saponins in traditional Chinese drug radix Astragali]

An analysis of the total saponins in 11 original species of Radix Astragali has been made. The results will be beneficial for drug control and resources utilization.

Heparin can activate a receptor tyrosine kinase

Heparin, a densely sulfated glycosaminoglycan produced by mast cells, is best known for its inhibitory effects on the blood coagulation system. Heparin or heparan sulfate proteoglycans are also essential cofactors for the interaction of fibroblast growth factors (FGFs) with their receptor tyrosine kinases (FGFRs). Here we show that heparin is a growth factor-independent activating ligand for FGFR-4. Heparin stimulates FGFR-4 autophosphorylation on transfected myoblasts, fibroblasts and lymphoid cells, and is most potent on cells lacking surface heparan proteoglycan. Two functional analogs of heparin, fucoidan and dextran sulfate, are also activators of FGFR-4, while neither heparin nor its analogs can stimulate FGFR-1 in the absence of FGF. A mutation in the FGFR-4 ectodomain which impairs receptor activation by FGFs does not interfere with activation by heparin, demonstrating that receptor domains required for heparin or FGF activation are not identical. Heparin activation of FGFR-4 or of a chimeric receptor bearing FGFR-4 ectodomain and FGFR-1 cytodomain triggers downstream tyrosine phosphorylation of several signaling proteins, and induces proliferation of cells bearing the chimeric receptor. Consistent with these findings, a soluble FGFR-4 ectodomain has strong FGF-independent affinity for immobilized heparin resin, while soluble FGFR-1 requires FGF for stable heparin interaction. Heparin activation of FGFR-4 is the first example of a mammalian polysaccharide serving as a signaling ligand.

Catalytic subunits of the porcine and rat 5'-AMP-activated protein kinase are members of the SNF1 protein kinase family

The 5'-AMP-activated protein kinase (AMPK) regulates the fatty acid and sterol synthesizing pathways via phosphorylation of acetyl-CoA carboxylase and HMG-CoA reductase, respectively. Highly purified kinase from porcine liver contains three apparent subunits of molecular mass 63 kDa, 40 kDa and 38 kDa. Peptide sequencing of the 63 kDa protein (AMPK63cat) revealed that this polypeptide is the catalytic subunit of the kinase. Porcine peptide sequences were used to clone by RT-PCR partial length cDNAs for the catalytic domains of the porcine AMPK63cat, and its rat homolog, which were virtually identical in deduced amino acid sequence. Screening of a rat liver cDNA library with these partial length cDNAs and with degenerate oligonucleotides yielded several unique clones, some of which had a 142 bp deletion in the catalytic domain of the kinase. A consensus full-length sequence with a 1.7 kb open reading frame has been constructed from overlapping library and PCR-derived clones. A large mRNA for rat AMPK63cat (8.5 kb) is expressed in nearly all rat tissues, with highest levels detectable in heart and skeletal muscle. Using PCR, the presence of two mRNA species with or without the 142 bp deletion in the catalytic domain was noted in all rat tissues examined. Comparison of the deduced protein sequence of AMPK63cat reveals highly conserved homologies in both the catalytic and non-catalytic domains to several members of the SNF1 kinase family, including kinases from Arabidopsis, barley, rye, and S. cerevesiae, as well as to other mammalian kinases and to a C. elegans kinase. The high evolutionary conservation of both kinase structure and function (metabolite sensing) coupled with their pattern of tissue/organism expression suggest that the mammalian members of this kinase family likely play wider roles than the regulation of cellular lipid metabolism.

In vivo detection of radicals in biological reactions

In vivo detection of free radicals on a quantitative basis is essential for an establishment of their role in membrane, protein, and cell and tissue damage. This article compares optical methods, including chemiluminescence, electron paramagnetic resonance (EPR) and NMR methods for the study of free radicals and free radical damage, especially reperfusion injury neutrophil accumulation 6 hr after the ischemia/reperfusion insult. The chemiluminescence method is applied to an evaluation of the improved resistance to free radical stress due to transfection of creatine kinase in the mouse liver.

Mammalian 5'-AMP-activated protein kinase non-catalytic subunits are homologs of proteins that interact with yeast Snf1 protein kinase

The 5'-AMP-activated protein kinase is responsible for the regulation of fatty acid synthesis by phosphorylation and inactivation of acetyl-CoA carboxylase. The porcine liver 5'-AMP-activated protein kinase 63-kDa catalytic subunit co-purifies 14,000-fold with a 38- and 40-kDa protein (Mitchelhill, K.I. et al. (1994) J. Biol. Chem. 269, 2361-2364). The 63-kDa subunit is homologous to the Saccharomyces cerevisiae Snf1 protein kinase, which regulates gene expression during glucose derepression. Peptide amino acid and polymerase chain reaction-derived partial cDNA sequences of both the pig and rat liver enzymes show that the 38-kDa protein is homologous to Snf4p (CAT3) and that the 40-kDa protein is homologous to the Sip1p/Spm/GAL83 family of Snf1p interacting proteins. Sucrose density gradient and cross-linking experiments with purified 5'-AMP-activated protein kinase suggest that both the 38- and 40-kDa proteins associate tightly with the 63-kDa catalytic polypeptide in either a heterotrimeric complex or in dimeric complexes. The 40-kDa subunit is autophosphorylated within the 63-kDa subunit complex. The sequence relationships between the mammalian 5'-AMP-activated protein kinase and yeast Snf1p extend to the subunit proteins consistent with conservation of the functional roles of these polypeptides in cellular regulation by this family of metabolite-sensing protein kinases.

[Reorganization of growth-plate-like tissue by isolated chondrocytes in culture]

Growth-plate cartilage is organized into four cellular zones containing resting, proliferating, maturing, and hypertrophic cells. Rabbit chondrocytes were isolated from growth-plate costal cartilage of 4-week-old New Zealand rabbits, the cells (15 x 10(4)) were suspended in 1 ml of Iscove's modified Dulbecco's medium (IMDM) with 10% fetal bovine serum, 50 micrograms ascorbic acid, and 60 micrograms kanamycin (medium A), then transferred to a 15 ml of plastic centrifuge tube, and centrifuged at 1500 rpm for 5 min. The cell pellet was incubated at 37 degrees C under 5% CO2 in air. The cultures reorganized into growth plate-like tissue which could be seen 7-14 days after cell seeding. This growth-plate, histologically, was organized longitudinally into cellular columns and horizontally into four cellular zones containing resting, proliferating, maturing and hypertrophic cells. The hypertrophic cells in the upper were large in size and round or oval in shape, the proliferating and the mature chondrocytes in the lower were small in size and spherical or elongated in shape. These chondrocytes were surrounded by an extensive matrix. Biochemically, DNA content of cultures began to rise on the 2nd day after cell seeding and reached a plateau after 10 days later. The uronic acid content increased from day 4 and reached the maximum on day 15. In contrast in the early culture, alkaline phosphatase activity was extremely low, it began to rise on day 9 and was the highest on day 20. The sequential increase of DNA, uronic acid and alkaline phosphatase contents was analogous to the in vivo changes of growth-plate chondrocytes.

Identification of an essential cysteine residue in pyridoxal phosphatase from human erythrocytes

Pyridoxal-specific phosphatase purified from human erythrocytes was inactivated by a variety of thiol-specific reagents in a time- and concentration-dependent manner. The presence of pyridoxal phosphate, a substrate, or inorganic phosphate, a competitive inhibitor, protected the enzyme from inactivation. Phosphatase inactivated by disulfide reagents was reactivated by the addition of excess dithiothreitol, indicating that the inactivation was due to formation of a mixed disulfide between the reagent and a free cysteinyl residue at or near the active site of the enzyme. Incorporation of either 1 mol of 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB), 0.6 mol of iodo[3H]acetate, or 0.6 mol of N-[3H]ethylmaleimide per mol of subunit led to complete inactivation of the enzyme. High concentration of phosphate prevented the incorporation of DTNB and iodo[3H]acetate. Amino acid analysis of carboxymethylated enzyme and DTNB titration of the denatured phosphatase indicated that there may be only 1 cysteinyl residue per subunit. Modification by iodoacetate did not affect the quaternary structure of the enzyme. The phosphatase modified by iodo[3H]acetate was subjected to trypsin digestion, and the resulting peptides were separated on a reverse phase C18 column. Two radioactive peaks were obtained and contained a peptide with the N-terminal sequence of Ala-Gln-Gly-Val-Leu-Phe-Asp-Cys(Cm)-Asp-Gly-Val-Leu-X-Asn-Gly. Most of the radioactivity was released with Cys(Cm). These results indicate that the cysteinyl residue in this sequence is at or near the active site and is essential for activity. Residues 5-12 and 15 of this peptide are identical with a sequence of a yeast alkaline p-nitrophenylphosphatase, and the peptide has little homology with other mammalian phosphatases.

Generation of selenium-containing abzyme by using chemical mutation

A new strategy for generating abzyme was developed. Glutathione peroxidase (GPX, EC 1.11.1.9) is one of the important members of antioxidation enzyme system; it catalyzes the reductions of a variety of hydroperoxides in presence of glutathione(GSH). We have first prepared the monoclonal antibody (McAb) with GSH binding sites, then incorporated GPX catalytic group selenocystein (SeCys) into the antibody combining sites by using chemical mutation. Thus the mutated antibody displays high GPX activity, which approaches the magnitude level of native GPX, exhibits the kinetic behavior similar to native GPX, and has some advantages over native GPX.