Real-time measurements of dark substrate catalysis

We have developed a novel procedure to monitor the real-time cleavage of natural unmodified peptides (dark substrates). In the competition-based assay, the initial cleavage rate of a fluorogenic peptide substrate is measured in the presence of a second substrate that is not required to exhibit any optical property change upon cleavage. Using a unique experimental design and steady-state enzyme kinetics for a two-substrate system, we were able to determine both Km and k(cat) values for cleavage of the dark substrate. The method was applied to HIV-1 protease and to the V82F/I84V drug resistant mutant enzyme. Using two different substrates, we showed that the kinetic parameters derived from the competition assay are in good agreement with those determined independently using standard direct assay. This method can be applied to other enzyme systems as long as they have one substrate for which catalysis can be conveniently monitored in real time.

Proline-Based P,N Ligands in Palladium-Catalyzed Asymmetric pi-Allyl Additions

Excellent yields and at least 95 % ee can be achieved for the addition of dimethyl malonate to cycloalkenyl acetates by using a palladium complex of the new phosphanyldihydrooxazole ligand L as a catalyst (see scheme). The ligand L can be synthesized from commercially available trans 4-hydroxy-L-proline in four steps. BOC=tert-butoxycarbonyl.

Drug resistance mutations can effect dimer stability of HIV-1 protease at neutral pH

The monomer-dimer equilibrium for the human immunodeficiency virus type 1 (HIV-1) protease has been investigated under physiological conditions. Dimer dissociation at pH 7.0 was correlated with a loss in beta-sheet structure and a lower degree of ANS binding. An autolysis-resistant mutant, Q7K/L33I/L63I, was used to facilitate sedimentation equilibrium studies at neutral pH where the wild-type enzyme is typically unstable in the absence of bound inhibitor. The dimer dissociation constant (KD) of the triple mutant was 5.8 microM at pH 7.0 and was below the limit of measurement (approximately 100 nM) at pH 4.5. Similar studies using the catalytically inactive D25N mutant yielded a KD value of 1.0 microM at pH 7.0. These values differ significantly from a previously reported value of 23 nM obtained indirectly from inhibitor binding measurements (Darke et al., 1994). We show that the discrepancy may result from the thermodynamic linkage between the monomer-dimer and inhibitor binding equilibria. Under conditions where a significant degree of monomer is present, both substrates and competitive inhibitors will shift the equilibrium toward the dimer, resulting in apparent increases in dimer stability and decreases in ligand binding affinity. Sedimentation equilibrium studies were also carried out on several drug-resistant HIV-1 protease mutants: V82F, V82F/I84V, V82T/I84V, and L90M. All four mutants exhibited reduced dimer stability relative to the autolysis-resistant mutant at pH 7.0. Our results indicate that reductions in drug affinity may be due to the combined effects of mutations on both dimer stability and inhibitor binding.

mdm-2 expression correlates with wild-type p53 status in esophageal adenocarcinoma

Several immunohistochemical studies showed that p53 protein is expressed in 50 to 80% of esophageal adenocarcinomas (EAs). Mutations of this tumor suppressor gene are present in 40 to 70% of EAs, so it is possible that p53 expression might occur as a result of mechanisms other than gene mutation. The human homologue of the murine double minute-2 gene (mdm-2) is a known regulator of p53 activity, and its expression results in stabilization of the wild-type p53 protein and loss of its tumor suppressor function. In this study, we evaluated the frequency of mdm-2 amplification and expression in EA and investigated the relationship between mdm-2 expression and p53 mutation. Thirty-three resection specimens of EAs and associated Barrett's esophagus were evaluated by immunohistochemical methods for p53 and mdm-2 expression. Sixteen of these cases were also evaluated for p53 mutations with use of polymerase chain reaction, single-strand conformational polymorphism, and DNA sequencing and for mdm-2 amplification with a differential polymerase chain reaction-based amplification analysis. Overexpression of p53 was present in 23 EAs (70%), and 18 EAs (55%) overexpressed mdm-2. p53 mutation was observed in 7 (43%) of 16 cases, whereas mdm-2 gene amplification was not detected in any. To summarize, we found substantial discordance of p53 immunohistochemical features and mutation in EA. Significant expression of mdm-2 occurred only in cases with wild-type p53, whereas all of the cases with p53 mutation showed little if any expression of mdm-2. Also, mdm-2 expression in cases with p53 overexpression but without p53 mutation exceeded mdm-2 expression in cases with p53 overexpression and p53 gene mutation. In cases without p53 mutation, overexpression of mdm-2 occurred in 50% of cases and might be responsible for stabilization of p53 protein and possible loss of tumor suppressor function.

[Morphological observations of the medial olivocochlear efferents in gerbils with chronic gentamicin ototoxicity]

OBJECTIVE

To determine the possible involvement of the medial olivocochlear efferents (MOC) in chronic aminoglycoside ototoxicity, the morphological changes of the MOC efferents in the cochlea of Mongolian gerbils and their correlations with the impairment of the outer hair cells (OHCs) were observed.

METHODS

The animals were given gentamicin in a dose of 150 mg/kg a day for 10 days. The distributions and densities of the MOC efferents were examined using the modified histochemical staining for acetylcholinesterase (AChE) and the numbers of OHCs were numerated with toluidine blue and Ehrlich haematoxylin staining on the surface preparation.

RESULTS

Significant damage to the MOC fibers and terminals as well as OHCs was noted in the basal turn of the cochlea, especially in those animals examined in 7th and 11th week after the gentamicin administration. The site of the greatest impairment of OHCs was consistent with that of the MOC efferents.

CONCLUSION

The results suggested that damage to the MOC efferents might play an important role in gentamicin-induced impairment of OHCs.

[Component in diphtheria-pertussis-tetanus-hepatitis B vaccine]

OBJECTIVE

To study immunogenecity of yeast-derived recombinant hepatitis B (YHB) component in diphtheria-pertussis-tetanus-YHB vaccine (DPTw-YHB).

METHODS

Immunogenecity of tetra-valent DTPw-YHB vaccine and mono-valent recombinant YHB vaccine, and that of the tetra-valent vaccine with varied YHB component were compared. The efficiency and stability of recombinant YHB in the tetra-valent vaccine stored at 2 - 8 degrees C for 18 months were determined.

RESULTS

The efficiency of recombinant YHB in the tetra-valent vaccine enhanced significantly in mice, as compared with that of mono-valent recombinant YHB vaccine, with an average mouse ED(50) of 1:2.0 - 1:3.1. There was no significant difference in efficiency of the tetra-valent vaccine with varied recombinant YHB component. Recombinant YHBin the DPTw-YHB tetra-valent vaccine still kept good stability stored at 2 - 8 degrees C for 18 months.

CONCLUSION

Recombinant YHB in the tetra-valent vaccine was more immunogenic than the mono-valent YHB vaccine. No interference and inhibition of DPTw to recombinant YHB was found, indicating good compatibility between DPTw and YHB.

Effect of cytokines on in vitro bone resorption by cells isolated from giant cell tumor of bone

OBJECTIVE

To investigate the effect of cytokines on in vitro bone resorption by cells isolated from giant cell tumor of bone.

METHODS

Mononuclear stromal cells and multinucleated giant cells (MGC) were isolated from 11 cases of giant cell tumor of bone (GCT) and their bone resorption capability in an in vitro cell-bone resorption model were tested. Expressions of some cytokines were detected by immunohistochemistry, Western blotting analysis and Enzyme-linked immunoabsorbent assay (ELISA) in the GCT.

RESULTS

The results showed that MGCs of GCT had capability to resorb bone matrix directly. Fibroblast-like stromal cells (FC) could not only resorb bone matrix directly, but also secret unknown factors to facilitate bone resorption of MGC. Exogenous TNF-alpha could significantly increase the bone resorption by both kinds of stromal cells, while exogenous IL-1 did not. Expression rate of M-CSF and level of TNF-alpha in GCT were higher than in osteosarcoma and normal serum.

CONCLUSIONS

The characteristic bone resorption behavior of GCT might be caused by its three major cell components. The M-CSF and TNF-alpha could promote their bone resorption capability.

[Utilization of a pedicled labial flap, single or double face, for the management of post-obstetric urethral damage]

Reported here is our experience with a single or double-face new procedure using a pedicled labial flap for urethral reconstruction in patients treated for extensive urethral damage after obstetrical injury. Between January 1992 to July 1997, 56 cases of urethral damage on African female patients, with an average age of 18 years old, were treated by pedicled labial urethroplasty. This procedure was done by using a single or double-face pedicled flap obtained from the major or minor labia. The flap was then introduced as in a tunnel beneath the vaginal epithelium reaching the damaged urethra. A variety of techniques were proposed: patch for sufficient lengthening (27 cases), tubularized flap allowing complete reconstruction of the urethra (18 cases) and the double-face urethroplasty (11 cases). Good quality urine continence was obtained by using the sub urethral Martius'sling procedure. In 11 cases, we combined the treatment with a colposuspension procedure. The average follow-up was 23 months (ranging from 5 to 47 months). The global success was 82% (52 patients treated). Recovery of normal miction and absence of urinary leak was obtained in 36 cases (69%). While 7 moderate failures occurred (13%), 9 cases were considered complete failures (17%). In view of the high success rate, we consider that the one-stage procedure by the use of a single or double face pedicled labial flap is a choice treatment and highly suitable for the management of extensive urethral cervical damage after obstetrical injury.

[Study on the human serums by absorption spectra]

The absorption spectra of normal human and cancer patient serums were measured, and those of human serum after adding some cancer cells were also measured. The results showed some difference in absorbance among the three kinds of serums. Some useful results were obtained.

Genetic polymorphism of human O6-alkylguanine-DNA alkyltransferase: identification of a missense variation in the active site region

O6-Alkylguanine-DNA alkyltransferase (AGT, EC 2.1.1.63) is a principle DNA repair protein in repairing O6-alkylguanine in DNA, a major premutagenic lesion produced by environmental and therapeutic alkylating agents. AGT plays a critical role in protecting cells against mutation and cytotoxicity induced by these alkylating agents. The existence of a large interindividual variation in human AGT activity level has been observed and we hypothesize that genetic polymorphism of AGT could be an important determinant for this variation. The present study reports the identification of a novel missense polymorphism in the human AGT gene. The polymorphic alteration occurs at codon 143 in exon 5, converting isoleucine (ATC) to valine (GTC). Because Ile143 is adjacent to the alkyl acceptor Cys145 of the AGT active site and is conserved among mammalian AGTs, amino acid substitution at this position may affect the function of AGT. The codon 143 polymorphism appears to be linked to another new polymorphic alteration at codon 178, which converts lysine (AAG) to arginine (AGG). Because it has been reported that human AGT can be truncated at position 176 without loss of activity, the codon 178 polymorphism may not affect AGT activity. The codon 143/178 polymorphism was found in two of 90 (2%) esophageal cancer patients residing in a high incidence area of China, but was not detected in 60 normal individuals residing in the same area. Six of 28 (210%) non-cancer Caucasian individuals, however, were found to carry this polymorphic allele, suggesting a significant ethnic difference in distribution of this codon 143/178 polymorphism between Chinese and Caucasian individuals. In addition, we confirmed the existence of a codon 84 genetic polymorphism previously identified in a Japanese population, which converts leucine (CTT) to phenylalanine (TTT). The distribution of codon 84 polymorphism was 16%, 20% and 36%, respectively, in the Chinese esophageal cancer patients, Chinese and Caucasian non-cancer individuals. Coexistence of codons 84 and 143/178 polymorphic alterations was found in one Caucasian individual. In all the Chinese (n = 150) and Caucasian (n = 28) samples examined, we were unable to detect a previously reported codon 160 polymorphism (Gly to Arg) which occurred in 10-25% of the Japanese individuals and was shown to affect the reaction of AGT with the drug O6-benzylguanine. The functional significance of the codon 143/178 genetic polymorphism of human AGT and its role in determining an individual's susceptibility to environmental alkylating carcinogens and response to alkylating chemotherapeutic drugs both remain to be studied.

[The submucosal structure of the endolymphatic sac of guinea pigs]

OBJECTIVE

To investigating the submucosal structure of the endolymphatic sac (ES), so as to analyse the role of ES in the function of inner ear.

METHOD

The temporal bone of the guinea pigs were cleared in methyl salicylate and inspected under a stereomicroscope. The ultrastructure of endolymphatic sac has been observed by transmission electron microscope.

RESULT

The extensive vascular system around the sac and has compact contact with sinus sigmoid. Its submucosal space comprises both arterioles and venules, as well as lymphatic sinus.

CONCLUSION

The result suggests that the ES is a very metabolically active structure and has a pressure regulating function. The disturbance of endolymphatic resorptive function seems to result endolymphatic hydrops after the vascular supply poverty of endolymphtic sac. It's may be the causative factor of Meniere's disease.

[Hair cell apoptosis and hearing loss of perilymphatic fistula]

OBJECTIVE

To investigate the effect of hair cell apoptosis on hearing loss of perilymphatic fistula (PLF) in guinea pig.

METHOD

Twenty-five guinea pigs with light microscope and TdT mediated biotin dUTP nick-end labelling (TUNEL) techniques. The ECochG and ABR were measured and the data analyzed with statistics.

RESULT

1. The apoptosis of hair cell was not revealed in 0-hour-group and 2-hour-group of PLF. Following the time of PLF was longer, the apoptosis of hair cell was more increased. The apoptosis of hair cell was demonsted in 1-day-group (1 case, 17%), 2-day-group (4 case, 67%) and 7-day-group (4 case, 80%); 2. The amplication of AP was reduced after operation induced PLF. The CAP of experimental ear was significantly higher than that of control ear (P < 0.01) in 1-day-group, 2-day-group and 7-day-group.

CONCLUSION

1. Apoptosis of hair cell was appeared in PLF; 2. The apoptosis of hair cell may be one of morphological evidence in hearing loss of PLF.

Functional characterization of the protease of human endogenous retrovirus, K10: can it complement HIV-1 protease?

To investigate the biochemical properties of the protease encoded by the human endogenous retrovirus, K10 (HERV-K), 213 amino acids of the 3'-end of the HERV-K protease (PR) open reading frame were expressed in Escherichia coli. Autocatalytic cleavage of the expressed polypeptide resulted in an 18.2 kDa protein which was shown to be proteolytically active against a fluorogenic peptide used as a substrate for HIV-1 protease. On the basis of sequence homology and molecular modeling, the 106 N-terminal amino acids of HERV-K PR were predicted to comprise a retroviral protease core domain. An 11.6 kDa protein corresponding to this region was expressed and shown to be a fully functional enzyme. The 11.6 kDa domain of HERV-K PR is unusually stable over a wide pH range, exhibits optimal catalytic activity between pH 4.0 and 5.0, and exists as a dimer at pH 7.0 with a Kd of 50 microM. Like HIV-1 PR, the HERV-K PR core domain is activated by high salt concentrations and processes HIV-1 matrix-capsid polyprotein at the authentic HIV-1 PR recognition site. However, both the 18.2 and 11.6 kDa forms of HERV-K PR were highly resistant to a number of clinically useful HIV-1 PR inhibitors, including ritonavir, indinavir, and saquinavir. This raises the possibility that HERV-K PR may complement HIV-1 PR during infection, and could have implications for protease inhibitor therapy and drug resistance.

[An analysis of hepatitis G virus infection status in various cases of hepatitis in Guangdong area]

To understand hepatitis G virus(HGV) infection status in different clinical types of hepatitis, 721 cases with hepatitis were analyzed in this article. PT-PCR technique was applied to amplify HGV gene, and heat denaturation method was used to extract HCV-RNA from sera. After turning to cDNA by reverse transcription(PT), a nested amplification was conducted and a 238 bp specific fragment was obtained. In this way, serum specimens of 721 cases with hepatitis, were tested including 587 hospitalized cases. 80 cases were found to be HGV RNA positive, of which positive rate of patients with non A-E hepatitis was high, HCV and HBV + HCV came the second, chronic severe hepatitis and liver cirrhosis (LC) was the lower. Results of research showed that HGV infection is prevalent to a certain degree among patients with viral hepatitis in Guangdong area.

[Diagnosis and treatment of Ramsay Hunt syndrome (a report of 39 cases)]

Thirty-nine cases with Ramsay Hunt syndrome were presented, in which 23 cases were firmly diagnosed early, and others were misdiagnosed to be Bell's palsy in 9 cases, sudden sensorineural hearing loss in 5, herpes zoster pharyngitis in 1 and acute suppurative otitis media in 1, respectively. All patients were treated with prednisone or dexamethasone for 3 weeks. The results of treatment were as follows: complete recovery in 27 cases, residual facial paralysis in 12 patients, in which 11 had sensorineural hearing loss. We concluded that: 1. When patients present idiopathic facial paralysis associated with objective sensorineural hearing loss, Hunt syndrome should be suspected even in the absence of vesicles. 2. Treatment with steroid and antiviral agent is needed. There is no significant difference in the effects between oral and intravenous steroid therapy. 3. The poor prognosis may relate with severe facial paralysis accompanying severe hearing loss. 4. Acoustic stapedius reflex in patients with mild or no hearing loss is useful for defining the involved sites and evaluating the prognosis.

[Immobilization of N-acetyl-1,6-diaminohexane(NADAH) on diol-silica and study of mechanism of NADAH and hexamethylene bisacetamide(HMBA) inducing tumor cells differentiation]

A method for separating NADAH and its immobilization onto diol-silica have been developed. HMBA and its meabolite NADAH were used as the inducers for many types of tumor cells' differentiation. The inducing mechanism of HMBA is not clear yet. Experiments show that HMBA and NADAH have a relatively strong hydrophobic reaction and hardly ion-exchange with some DNA and some proteins of the cytosolic fraction of HL-60 human acute progranulocytic leukemia cells, BIU-87 human bladder carcinoma cells and the human erythrocyte membrane, when utilizing immobilization of NADAH. The retention time of the proteins and DNA was longer than that of the phosphatides. These results show that the adsorption of HMBA and NADAH with some proteins and DNA is higher than that with the phosphatides. The expected receptor binding biospecifically with HMBA has not been found.

Lidocaine prolongs the safe duration of circulatory arrest during deep hypothermia in dogs

PURPOSE

To test the hypothesis that lidocaine prolongs the safe period of circulatory arrest during deep hypothermia.

METHODS

Sixteen dogs were subjected to cooling, first surface cooling to 30 degrees C and then core cooling to 20 degrees C rectal temperature). The circulation was then stopped for 90 min. In the lidocaine group, 4 mg.kg-1 lidocaine was injected into the oxygenator two minutes before circulatory arrest and 2 mg.kg-1 at the beginning of reperfusion and rewarming. The control group received equivalent volumes of normal saline. Post-operatively, using a neurological deficit scoring system (maximum deficit score-100; minimum-zero indicating that no scored deficit could be detected). Neurological function was evaluated hourly for six hours and then daily for one week, the pharmacokinetic parameters were calculated using one compartment model.

RESULTS

On the seventh day, the neurological deficit score and overall performance were better in the lidocaine (0.83 +/- 2.04) than in the control group (8.33 +/- 4.08 P < 0.05). During the experiment, the base excess values were also better in the lidocaine than in the control group (at 30 min reperfusion: -4.24 +/- 1.30 vs -8.20 +/- 2.82 P < 0.01, at 60 min reperfusion was -3.34 +/- 1.87 vs -7.52 +/- 2.40 (P < 0.01). On the eighth day the extent of pathological changes were milder in the lidocaine group than that in the control group. The elimination half life of lidocaine was 40.44 +/- 7.99 during hypothermia and 2.01 +/- 4.56 during rewarming.

CONCLUSIONS

In dogs lidocaine prolongs the safe duration of circulatory arrest during hypothermia.

Thermodynamics of a transition state analogue inhibitor binding to Escherichia coli chorismate mutase: probing the charge state of an active site residue and its role in inhibitor binding and catalysis

Electrostatic interactions play important roles in the catalysis of chorismate to prephenate by chorismate mutase. Mutation of Gln88 to glutamate in the monofunctional chorismate mutase from Escherichia coli results in an enzyme with a pH profile of activity significantly different from that of the wild type protein. To investigate whether the mutation alters the substrate binding process or the catalysis, we have directly determined the thermodynamic parameters of a transition state analogue inhibitor binding to the wild-type chorismate mutase and its Q88E mutant using isothermal titration calorimetry. The results demonstrate that solvent reorganization and hydrophobic interactions contribute the predominant free energy to inhibitor binding. The charge state of Glu88 in the Q88E mutant was experimentally determined and was shown to be protonated at pH 4.5 and ionized at pH 7.8, consistent with earlier hypotheses. Most surprisingly, inhibitor binding energetics do not exhibit significant pH dependency for both enzymes. Our findings indicate that the charge state of Glu88 has a small impact on inhibitor binding but plays an important role in the catalytic process.

[Spectroscopic characterization of a new terbium complex with red fluorescence]

Usually, the emission spectra of terbium complexes exhibit 490 nm, 545 nm bands (green color) under the excitation of UV light, which is ascribed to the two 5D4 - 7F6, 5D4 - 7F5 transition. In this report, pink red fluorescence under the excitation of 300-370nm UV light is observed for a new 1, 10-phenanthroline-2-naphthoate complex of terbium. The fluorescence, FT-IR, ICP and X-ray fluorescence analysis were performed. The results showed that under the perturbation of the ligands field, the probability of 5D4 - 7F3 transition of terbium ion was greatly enhanced, while the probability of 5D4 - 7F5 transition was greatly decreased in the complex. Therefore, pink-red fluorescence was observed for the title complex.

[Investigation on the luminescence properties of Er ions in Er-doped sol-gel silica glasses]

Er-doped sol-gel silica glasses which have room temperature photoluminescence at 1.54 microm and doped concentration of 10(20)/cm(3) have been prepared. The examination results Indicated: (1) PL spectrum has largest intensity at the 0.5W% doped concentration; (2) the intensity of PL decreased 74%, when the temperature raised form 4K to 300K; (3) The Er ion and O ions formed complexes with coordinated numbers of 8 or 9.

[Study on the relationship between deoxyribonucleoside triphosphate (dNTP) pools and cell transformation]

Deoxyribonucleoside triphosphate (dNTP) pools were measured in normal BALB/c3T3 cells, transformation-treated cells and transformed cells with reverse-phase HPLC. The fluctuation of dNTP pools was similar after cells were treated with alkylating mutagens glycidyl methacrylate (GMA) and N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). The gap between (dGTP + dATP) pools and (dTTP + dCTP) pools was greatly intensified. The measurements also indicated that the dNTP pools in transformed cells were quite different from those in normal cells. The results suggest that dNTP pools may play an important role in cell transformation.

[Purification and properties of antifungal protein X98III from Bacillus subtilis]

Bacillus subtilis BS-98 is one of the antagonistic strains strongly against plant fungal pathogens such as Physalospora piricola Nose. The antifungal protein was purified by ammonium sulphate precipitation and column chromatography on Sephadex G-100 and DEAE-cellulose, and it was named X98III. Molecular weight of X98III is 59,000 by SDS-PAGE and PI value is 4.50 by PAG-IEF, respectively. X98III was demonstrated as glycoprotein and lipoprotein by CAM (cellulose acetate membrane) electrophoresis and special staining. We estimated it contains 6% saccharides by using DNS methods. This protein was also found to be thermostabale and partially sensitive to proteinases. The amino acid analysis of the protein X98III showed that it comprises of 11 different amino acids and Glu, Tyr, Cys are the abundant amino acids. No Asp, Phe and Met were found. Purified X98III has strong inhibiting activity against the pathogens of Physalospora piricola, Phoma asparagi, etc. The antifungal mechanism of X98III was mainly disintegration of the cell wall to make the hyphae abnormal and the spores germinate abnormally or can not germinate at all.

Dissection of the pH dependence of inhibitor binding energetics for an aspartic protease: direct measurement of the protonation states of the catalytic aspartic acid residues

The catalytic activity and inhibitor binding energetics of enzymes are often pH-dependent properties. Aspartic proteases comprise an important class of enzyme targets for structure-based drug design. We have performed a complete thermodynamic study of pepstatin binding to plasmepsin II, an aspartic proteinase found in Plasmodium falciparum, using isothermal titration calorimetry and circular dichroism. Thermodynamic parameters (DeltaG, DeltaH, DeltaCp, and DeltaS) were measured as functions of both pH and temperature. In the pH range from 4.5 to 7.0, pepstatin binding is accompanied by proton transfer between the solvent and the complex. We used thermodynamic proton linkage theory to derive both the pH-independent binding energetics for pepstatin and the number and pKa values of ionizable residues whose pKa values change during ligand binding. These residues were identified as the two catalytic aspartates, with pKas of 6.5 and 3.0, and His 164, with a pKa of 7.5, based on the three-dimensional structure of the pepstatin-plasmepsin II complex. At pH 5.0, where the protease has optimum activity, the proton transfer process contributes almost 40% of the total binding free energy change and the total charge of the active-site aspartic acid residues is -1. These experimental results provide direct measurement for the protonation states of the catalytic aspartates in the presence of bound ligands. Comparison of the thermodynamic and structural data for pepstatin binding with human cathepsin D, a lysosomal aspartic protease that shares 35% sequence identity with plasmepsin II, suggests that the energetic differences between these two proteins are due to a higher interdomain flexibility in plasmepsin II.

[Promotive effect of TNF-alpha and M-CSF on osteolysis induced by giant cell tumor of bone]

OBJECTIVE

To explore the effect of cell components in giant cell tumor of bone (GCT) and cytokines expressed by them on osteolysis.

METHODS

Mononuclear stromal cells and multinucleated giant cells (MGCs) were isolated from 10 cases of GCT, and fibroblast-like stromal cells were obtained by long-term culture of mononuclear stromal cells. Osteolytic capability of above isolated cells were tested in an in vitro cell-bone resorption model.

RESULTS

All cell components isolated from GCT had capability to resorb bone matrix directly. Exogenous tumore necrosis factor-alpha (TNF-alpha) could significantly increase the bone resorption induced by both kinds of stromal cell. There were higher level of TNF-alpha and greater expression rate of macrophage colony stimulating factor (M-CSF) in GCT than in the osteosarcoma tissues or the normal serum.

CONCLUSIONS

The characteristic bone resorption behavior of GCT might be conducted by all it's three major cell components, and this bone resorption process could be promoted by both TNF-alpha and M-CSF they expressed.