Hydrolysis of the isopeptide epsilon-(gamma-glutamyl)-lysine by destabilase from the medicinal leech Hirudo medicinalis

Using amino acid analysis, the ability of destabilize to hydrolyze the epsilon-(gamma-Glu)-Lys isopeptide bond was demonstrated. Incubation of the epsilon-(gamma-Glu)-Lys isopeptide with the enzyme was accompanied by a decrease of the amount of the isopeptide and an increase of equimolar amounts of lysine and glutamic acid. Complete hydrolysis of the isopeptide was observed after 96 hour incubation with destabilize. It was supposed that the isopeptide is a less specific substrate for destabilize compared to L-gamma-Glu-pNA.     

Synthesis and secretion of active lipoprotein lipase in Chinese-hamster ovary (CHO) cells.

Cultured Chinese-hamster ovary cells (CHO cells) were found to produce and secrete a lipase, which was identified as a lipoprotein lipase by the following criteria. Its activity was stimulated by serum and apolipoprotein CII, and was inhibited by high salt concentration. The lipase bound to heparin-agarose and co-eluted with 125I-labelled bovine lipoprotein lipase in a salt gradient. A chicken antiserum to bovine lipoprotein lipase inhibited the activity and precipitated a labelled protein of the same apparent size as bovine lipoprotein lipase from media of CHO cells labelled with [35S]methionine. The lipase activity and secretion were similar in growing cells and in cells that had reached confluency. Hence, lipoprotein lipase appears to be expressed constitutively in CHO cells and is not linked to certain growth conditions, as in pre-adipocyte and macrophage cell lines. At 37 degrees C, but not at 4 degrees C, heparin increased the release of lipase to the medium 2-4-fold. This increased release occurred without depletion of cell-associated lipase activity, suggesting that heparin enhanced release of newly synthesized lipase.     

Polyamine-mediated turnover of ornithine decarboxylase in Chinese-hamster ovary cells.

The major secreted isoenzyme of human prostatic acid phosphatase (PAcP) (EC 3.1.3.2), which catalyses p-nitrophenyl phosphate (PNPP) hydrolysis at acid pH values, was found to have phosphotyrosyl protein phosphatase activity since it dephosphorylated three different phosphotyrosine-containing protein substrates. Several lines of evidence are presented to show that the phosphotyrosyl phosphatase and PAcP are the same enzyme. A highly purified PAcP enzyme preparation which contains a single N-terminal peptide sequence was used to test for the phosphotyrosyl phosphatase activity. Both activities comigrated during gel filtration by high performance liquid chromatography. Phosphotyrosyl phosphatase activity and PNPP acid phosphatase activity exhibited similar sensitivities to different effectors. Both phosphatase activities showed the same thermal stability. Specific anti-PAcP antibody reacted to the same extent with both phosphatase activities. PNPP acid phosphatase activity was competitively inhibited by the phosphotyrosyl phosphatase substrate. To characterize further the phosphotyrosyl phosphatase activity, the Km values using different phosphoprotein substrates were determined. The apparent Km values for phosphorylated angiotensin II, anti-pp60src immunoglobulin G and casein were in the nM range for phosphotyrosine residues, which was about 50-fold lower than the Km for phosphoserine residues in casein.     

Isolation, characterization and seasonal variations in the concentration of N-epsilon-(gamma-glutamyl)-lysine isodipeptide in the blood plasma of the winter flounder (Pseudopleuronectes americanus).

A ninhydrin-positive compound was isolated from the plasma of the winter flounder (Pseudopleuronectes americanus) and identified as the isodipeptide N-epsilon-(gamma-glutamyl)-lysine. Wide seasonal variations in plasma concentration of this compound are found in the male flounder, whereas it is present only in trace amounts in the plasma of the female flounder throughout the year. In the male flounder the plasma concentration of N-epsilon-(gamma-glutamyl)-lysine rises from January to a peak in May and June. It is during these latter months that the flounder spawn. After spawning, the plasma concentration of the isodipeptide decreases to low basal values in October. These changes in plasma concentration of N-epsilon-(gamma-glutamyl)-lysine may be related to changes in testes weight, spermatogenesis and spawning activity of the winter flounder.     

Degradation of cells dying by apoptosis leads to accumulation of epsilon(gamma-glutamyl)lysine isodipeptide in culture fluid and blood.

epsilon(gamma-Glutamyl)lysine isodipeptide, the end-product of proteolytic digestion of proteins cross-linked by transglutaminase, was detected in culture fluid of neonatal rat hepatocytes and plasma of adult rats. The concentration of the isodipeptide was significantly increased in both when high rate of apoptosis with phagocytosis of dying hepatocytes was produced either by epidermal growth factor in the culture or by lead nitrate-induced hyperplasia with subsequent involution in rats. Specific induction of tissue transglutaminase and the consequent formation of highly cross-linked protein envelopes in apoptotic cells have been previously demonstrated by us in both systems.     

Transport and accumulation of 2-deoxy-D-glucose in wild-type and hexokinase-deficient cultured Chinese-hamster ovary (CHO) cells.

Hexokinase-deficient mutants and wild-type Chinese-hamster ovary cells have been used to investigate the role of hexokinase in uptake and accumulation of 2-D-deoxyglucose (2-dGlc). The evidence for a specific sugar transport system in both types of cells is that there is similar saturable phloretin-sensitive uptake of 2-dGlc and 3-O-methyl-D-glucose (3-OMG) in both types of cell. In wild-type cells, 2-dGlc is accumulated to a tissue:medium ratio of 10- and in the mutant only 3-fold; 3-OMG is not accumulated by either mutant or wild-type cells. The evidence that hexokinase affects the membrane transport process is that the rate of exit of free 2-dGlc from wild-type cells is 5-fold less than from mutant cells, whereas there is no difference in the rate of loss of 3-OMG between mutant and wild-type cells.     

Age-dependent accumulation of N epsilon-(carboxymethyl)lysine and N epsilon-(carboxymethyl)hydroxylysine in human skin collagen

N epsilon-(Carboxymethyl)lysine (CML) is formed on oxidative cleavage of carbohydrate adducts to lysine residues in glycated proteins in vitro [Ahmed et al. (1988) J. Biol. Chem. 263, 8816-8821; Dunn et al. (1990) Biochemistry 29, 10964-10970]. We have shown that, in human lens proteins in vivo, the concentration of fructose-lysine (FL), the Amadori adduct of glucose to lysine, is constant with age, while the concentration of the oxidation product, CML, increases significantly with age [Dunn et al. (1989) Biochemistry 28, 9464-9468]. In this work we extend our studies to the analysis of human skin collagen. The extent of glycation of insoluble skin collagen was greater than that of lens proteins (4-6 mmol of FL/mol of lysine in collagen versus 1-2 mmol of FL/mol of lysine in lens proteins), consistent with the lower concentration of glucose in lens, compared to plasma. In contrast to lens, there was a slight but significant age-dependent increase in glycation of skin collagen, 33% between ages 20 and 80. As in lens protein, CML, present at only trace levels in neonatal collagen, increased significantly with age, although the amount of CML in collagen at 80 years of age, approximately 1.5 mmol of CML/mol of lysine, was less than that found in lens protein, approximately 7 mmol of CML/mol of lysine. The concentration of N epsilon-(carboxymethyl)hydroxylysine (CMhL), the product of oxidation of glycated hydroxylysine, also increased with age in collagen, in parallel with the increase in CML, from trace levels at infancy to approximately 5 mmol of CMhL/mol of hydroxylysine at age 80.(ABSTRACT TRUNCATED AT 250 WORDS)     

Carbohydrate structures of the human-immunodeficiency-virus (HIV) recombinant envelope glycoprotein gp120 produced in Chinese-hamster ovary cells.

The present paper describes the structures of the N-linked oligosaccharides of the human-immunodeficiency-virus (HIV) envelope glycoprotein gp120 (cloned from the HTLV-III B isolate and expressed as a secreted fusion protein after transfection of Chinese-hamster ovary cells), which is known to bind with high affinity to human T4-lymphocytes. Oligosaccharides were released from peptide by hydrazinolysis, fractionated by paper electrophoresis, high-performance lectin-affinity chromatography and Bio-Gel P-4 column chromatography, and their structures determined by sequential exoglycosidase digestions in conjunction with methylation analysis. The glycoprotein was found to be unique in its diversity of oligosaccharide structures. These include high-mannose type and hybrid type, as well as four categories of complex-type chains: mono-, bi-, tri- and tetra-antennary, with or without N-acetyl-lactosamine repeats, and with or without a core-region fucose residue. Among the sialidase-treated oligosaccharides, no less than 29 structures were identified as follows: (formula; see text) where G is galactose, GN is N-acetylglucosamine, M is mannose, F is fucose, and '+/- ' means that residues are present in a proportion of chains. The actual number of oligosaccharide structures is much greater, since before desialylation there was evidence that, among the hybrid and complex-type chains, all but 6% contained sialic acid at the C-3 position of terminal galactose residues, and partially sialylated forms of the bi- and multi-antennary chains were present. Detailed evidence for the proposed oligosaccharide sequences will be published as a supplementary paper [T. Mizuochi, M. W. Spellman, M. Larkin, J. Solomon, L. J. Basa & T. Feizi (1988) Biomed. Chromatogr., in the press].     

Phospholipid turnover during cell-cycle traverse in synchronous Chinese-hamster ovary cells. Mitogenesis without phosphoinositide breakdown.

The turnover of phospholipids was investigated in quiescent serum-starved Chinese-hamster ovary (CHO-K1) cells stimulated to progress through the cell cycle by the addition of dialysed bovine serum. A variety of radiolabelling techniques were employed to study the rapid effects of serum on phospholipids and later events during G1 and S phases of the cell cycle. Pulse-labelling studies using [32P]Pi revealed that there was a stimulation of the synthesis rate of all phospholipids investigated during the initial few hours after serum addition. The greatest stimulation (20-fold) was observed in phosphatidylcholine, and the smallest in the polyphosphoinositides (PPIs). Mock stimulation with serum-free medium caused a similar increase in PPI turnover, but little or no effect on turnover of other phospholipids. This effect could be accounted for by a stimulation of the turnover of cellular ATP pools increasing [32P]ATP specific radioactivity. Late G1 and S phases were associated with a decrease in the rate of synthesis of all phospholipids. Phosphatidic acid was the only phospholipid whose labelling fell below that in mock-stimulated cells during the period of the cell cycle. Stimulation of serum-starved cells that had been prelabelled with myo-[2-3H]inositol caused no change in the amounts of inositol trisphosphate, but both serum-stimulated and mock-stimulated cells exhibited similar small decreases in both inositol bisphosphate and inositol monophosphate, of approx. 30% after 30 s. When cells were serum-stimulated in the presence of 10 mM-Li+, there was no increase in the size of the total inositol phosphate pool. We conclude that mitogenic stimulation and cell-cycle traverse cause profound and complex effects on phospholipid turnover in CHO-K1 cells, but there is no evidence for a role of inositol lipid turnover in the proliferative response to serum in this cell line.     

Expression of the cDNA encoding for mouse sperm-specific lactate dehydrogenase C in Chinese-hamster ovary cells.

The cloned cDNA encoding for mouse sperm-specific lactate dehydrogenase C (LDH-C) was inserted immediately downstream to the MMTV 5' LTR promoter, and it was shown to synthesize mouse LDH-C polypeptide in Chinese-hamster ovary cells. The mouse LDH-C subunit and the endogenous Chinese-hamster LDH-A subunit formed in vivo a heterotetrameric LDH-A3C1 isoenzyme, and this novel isoenzyme exhibited enzymic activity utilizing lactate as substrate.     

Lectin affinity chromatography of glycopeptides and oligosaccharides from normal and lectin-resistant Chinese-hamster ovary cells.

The [3H]mannose-labelled glycopeptides from two lectin-resistant lines of Chinese-hamster ovary cells were fractionated by chromatography on lentil lectin-Sepharose and concanavalin A-agarose columns and subsequently analysed by gel filtration in comparison with the glycopeptides of the parental cell line. Essentially all of the [3H]mannose-labelled asparaginyl-oligosaccharides from the 'single-mutant' cells selected for resistance to phytohaemagglutinin and the 'double-mutant' cells selected for additional resistance to concanavalin A were not bound to lentil lectin, whereas approximately one-sixth of the parental-cell glycopeptides were bound and specifically eluted with alpha-methyl mannoside. These bound and eluted glycopeptides represented a specific subset of the complex acidic-type asparaginyl-oligosaccharides. The percentage of radiolabelled glycopeptides and oligosaccharides from each cell line that were specifically bound to concanavalin A was consistent with the relative sensitivities of the three cell lines to this lectin. The major radiolabelled species in the endoglycosidase digest of the 'double-mutant'-cell glycopeptides (Man4GlcNAc1-size neutral oligosaccharides) were not bound to concanavalin A, whereas essentially all of the other neutral-type oligosaccharides were bound. In addition, the larger neutral-type oligosaccharides (Man8--9GlcNAc1) were more strongly bound to concanavalin A than were either the smaller neutral-type or the di-antennary acidic-type structures.     

The rate of deoxyribonucleic acid synthesis by cultured Chinese-hamster ovary cells. An application of isotope-dilution analysis.

The rate of DNA synthesis is exponentially growing cells was determined by isotopedilution analysis of the incorporation of [me-3H]thymidine. Thymidine concentrations greater than 7 micrometer were used so that the rate-limiting step governing incorporation would be at the level of DNA polymerase rather than at the level of thymidine kinase [Sjostrom & Forsdyke (1974) Biochem. J. 138, 253-262]. In early exponential phase the rate determined by isotope-dilution analysis closely correlated with the rates calculated either from growth curves or from known cell-cycle parameters. However, in late-exponential phase the rate calculated from the growth curve was less than that determined by isotope-dilution analysis. We conclude that, under certain conditions, the pool-corrected rate of incorporation of [me-3H]thymidine, as determined by isotope-dilution analysis, can accurately reflect the rate of DNA synthesis. Discrepancies between the observed rate of DNA synthesis and increase in cell number could reflect an exponential degeneration of post-S-phase cells.     

Isolation of peptides containing citrulline and the cross-link, epsilon-(gamma-glutamyl)lysine, from hair medulla protein.

The epsilon-(gamma-glutamyl)lysine cross-link has been unequivocally localized in the citrulline-containing protein of hair medulla tissue. This was achieved by the isolation of cross-linked peptides that contain citrulline. The peptides were purified by molecular sieving, cation-exchange and paper chromatography and paper electrophoresis and their amino acid compositions are reported. They were detected by analyzing a large number obtained from a tryptic digest of thermolytic peptides of the medulla protein. There is no evidence at present as to whether the cross-link is in fact inter- or intrachain, or both.     

Synthesis of N epsilon-(7-diethylaminocoumarin-3-carboxyl)- and N epsilon-(7-methoxycoumarin-3-carboxyl)-L-Fmoc lysine as tools for protease cleavage detection by fluorescence.

Two coumarin-labelled lysines were conveniently prepared as a fluorescence resonance energy transfer (FRET) pair for peptide cleavage detection. 7-Methoxy and 7-diethylamino coumarin-3-carboxylic acids were synthesized according to a modification of known procedures. Labelling at lysine was achieved in solution via the active N-hydroxysuccinimide ester of the carboxylic acid coumarin derivatives to give the target compounds in good yield. Subsequently, these modified amino acids were used in solid phase peptide synthesis (SPPS), and their potential utility in an extracellular matrix metalloprotease (MMP-1) activity measurement via FRET and/or quenching studies was demonstrated.     

Polyamine starvation causes accumulation of cadaverine and its derivatives in a polyamine-dependent strain of Chinese-hamster ovary cells.

Starvation of the polyamine-dependent Chinese-hamster ovary cells for ornithine or ornithine-derived polyamines in serum-free culture resulted in the formation of cadaverine and its aminopropyl derivatives, N-(3-aminopropyl)cadaverine and NN'-bis(3-aminopropyl)cadaverine. The synthesis of these unusual amines was inhibited by treatment of the cells with DL-2-difluoromethylornithine, a specific inhibitor of ornithine decarboxylase (EC 4.1.1.17). In the absence of ornithine (the normal substrate), ornithine decarboxylase thus appeared to catalyse the decarboxylation of lysine to cadaverine. Cell proliferation was markedly inhibited by ornithine deprivation of the cells, and further depressed by exposure of the cultures to difluoromethylornithine.