Enzyme kinetics of cytochrome P450-mediated reactions

The most common drug-drug interactions may be understood in terms of alterations of metabolism, associated primarily with changes in the activity of cytochrome P450 (CYP) enzymes. Kinetic parameters such as Km, Vmax, Ki and Ka, which describe metabolism-based drug interactions, are usually determined by appropriate kinetic models and may be used to predict the pharmacokinetic consequences of exposure to one or multiple drugs. According to classic Michaelis-Menten (M-M) kinetics, one binding site models can be employed to simply interpret inhibition (pure competitive, non-competitive and uncompetitive) or activation of the enzyme. However, some cytochromes P450, in particular CYP3A4, exhibit unusual kinetic characteristics. In this instance, the changes in apparent kinetic constants in the presence of inhibitor or activator or second substrate do not obey the rules of M-M kinetics, and the resulting kinetics are not straightforward and hamper mechanistic interpretation of the interaction in question. These unusual kinetics include substrate activation (autoactivation), substrate inhibition, partial inhibition, activation, differential kinetics and others. To address this problem, several kinetic models can be proposed, based upon the assumption that multiple substrate binding sites exist at the active site of a particular P450, and the resulting kinetic constants are, therefore, solved to adequately describe the observed interaction between multiple drugs. The following is an overview of some cytochrome P450-mediated classic and atypical enzyme kinetics, and the associated kinetic models. Applications of these kinetic models can provide some new insights into the mechanism of P450-mediated drug-drug interactions.

Drug transport by reconstituted P-glycoprotein in proteoliposomes. Effect of substrates and modulators, and dependence on bilayer phase state

The P-glycoprotein multidrug transporter (Pgp) is an active efflux pump for chemotherapeutic drugs, natural products and hydrophobic peptides. Pgp is envisaged as a 'hydrophobic vacuum cleaner', and drugs are believed to gain access to the substrate binding sites from within the membrane, rather than from the aqueous phase. The intimate association of both Pgp and its substrates with the membrane suggests that its function may be regulated by the biophysical properties of the lipid bilayer. Using the high affinity fluorescent substrate tetramethylrosamine (TMR), we have monitored, in real time, transport in proteoliposomes containing reconstituted Pgp. The TMR concentration gradient generated by Pgp was collapsed by the addition of either the ATPase inhibitor, vanadate, or Pgp modulators. TMR transport by Pgp obeyed Michaelis--Menten kinetics with respect to both of its substrates. The Km for ATP was 0.48 mM, close to the K(m) for ATP hydrolysis, and the K(m) for TMR was 0.3 microM. TMR transport was inhibited in a concentration-dependent fashion by verapamil and cyclosporin A, and activated (probably by a positive allosteric effect) by the transport substrate colchicine. TMR transport by Pgp reconstituted into proteoliposomes composed of two synthetic phosphatidylcholines showed a highly unusual biphasic temperature dependence. The rate of TMR transport was relatively high in the rigid gel phase, reached a maximum at the melting temperature of the bilayer, and then decreased in the fluid liquid crystalline phase. This pattern of temperature dependence suggests that the rate of drug transport by Pgp may be dominated by partitioning of drug into the bilayer.

Herpes simplex virus virion host shutoff protein requires a mammalian factor for efficient in vitro endoribonuclease activity

The virion host shutoff protein (vhs) of herpes simplex virus (HSV) triggers global shutoff of host protein synthesis and accelerated mRNA turnover during virus infection and induces endoribonucleolytic cleavage of exogenous RNA substrates when it is produced in a rabbit reticulocyte (RRL) in vitro translation system. Although vhs induces RNA turnover in the absence of other HSV gene products, it is not yet known whether cellular factors are required for its activity. As one approach to addressing this question, we expressed vhs in the budding yeast Saccharomyces cerevisiae. Expression of vhs inhibited colony formation, and the severity of this effect varied with the carbon source. The biological relevance of this effect was assessed by examining the activity of five mutant forms of vhs bearing previously characterized in-frame linker insertions. The results indicated a complete concordance between the growth inhibition phenotype in yeast and mammalian host cell shutoff. Despite these results, expression of vhs did not trigger global mRNA turnover in vivo, and cell extracts of yeast expressing vhs displayed little if any vhs-dependent endoribonuclease activity. However, activity was readily detected when such extracts were mixed with RRL. These data suggest that the vhs-dependent endoribonuclease requires one or more mammalian macromolecular factors for efficient activity.

beta-Amyloid efflux mediated by p-glycoprotein

A large body of evidence suggests that an increase in the brain beta-amyloid (Abeta) burden contributes to the etiology of Alzheimer's disease (AD). Much is now known about the intracellular processes regulating the production of Abeta, however, less is known regarding its secretion from cells. We now report that p-glycoprotein (p-gp), an ATP-binding cassette (ABC) transporter, is an Abeta efflux pump. Pharmacological blockade of p-gp rapidly decrease extracellular levels of Abeta secretion. In vitro binding studies showed that addition of synthetic human Abeta1-40 and Abeta1-42 peptides to hamster mdr1-enriched vesicles labeled with the fluorophore MIANS resulted in saturable quenching, suggesting that both peptides interact directly with the transporter. Finally, we were able to directly measure transport of Abeta peptides across the plasma membranes of p-gp enriched vesicles, and showed that this phenomenon was both ATP- and p-gp-dependent. Taken together, our study suggests a novel mechanism of Abeta detachment from cellular membranes, and represents an obvious route towards identification of such a mechanism in the brain.

Excretion pattern investigation of urinary normal and modified nucleosides of breast cancer patients by RP-HPLC and factor analysis method

Modified nucleosides, formed post-transcriptionally in RNA by a number of modification enzymes, are excreted in abnormal levels in the urine of patients with malignant tumors. To test their usefulness as tumor markers, and to compare them with the conventional tumor markers, a reversed-phase high-performance liquid chromatographic (RP-HPLC) method and a factor analysis method have been used to study the excretion pattern of nucleosides of breast cancer patients. A clear cut differentiation of the breast cancer group and the healthy individuals in two clusters without overlapping was obtained.

Concentrations and flux of rare earth elements in a semifield plot as influenced by their agricultural application

The concentrations of rare earth elements (REs) in atmospheric particles, soil, soil water, surface runoff, and different parts of corn in an experimental plot in the suburb of Beijing, China were measured and the flux of REs was estimated. The concentration of REs in air particles with diameter less than 10 microm is 36 ng/m3 and, by ratio analysis, the origin of REs in the atmosphere was likely local soil. The concentration of soluble REs is 0.69 microg/L in rainwater, 5-7 microg/L in surface runoff, as well as 1-4 microg/L in soil water and the application of RE mixture has no observed influences on their concentrations. The concentration of soluble REs in surface runoff and soil water was dominated by aqueous-solid-phase partitioning. By estimation of the flux, most of the REs applied will remain in the soil phase and continued application of REs will cause an accumulation of REs in agricultural soil.

The vhs1 mutant form of herpes simplex virus virion host shutoff protein retains significant internal ribosome entry site-directed RNA cleavage activity

The virion host shutoff (vhs) protein of herpes simplex virus (HSV) triggers global shutoff of host protein synthesis and accelerated turnover of host and viral mRNAs during HSV infection. As well, it induces endoribonucleolytic cleavage of RNA substrates when produced in a rabbit reticulocyte lysate (RRL) in vitro translation system. The vhs1 point mutation (Thr 214-->Ile) eliminates vhs function during virus infection and in transiently transfected mammalian cells and was therefore previously considered to abolish vhs activity. Here we demonstrate that the vhs1 mutant protein induces readily detectable endoribonuclease activity on RNA substrates bearing the internal ribosome entry site of encephalomyocarditis virus in the RRL assay system. These data document that the vhs1 mutation does not eliminate catalytic activity and raise the possibility that the vhs-dependent endoribonuclease employs more than one mode of substrate recognition.

Accumulation of rare earth elements in corn after agricultural application

Using both pot and plot experiments, the dose-dependent accumulation of rare earth elements (REs) in corn (Zea mays L.) after application of an agricultural REs mixture was measured. In the pot experiment, the dose-dependent accumulation of REs in corn root and stem was observed, but it could not be detected in corn leaf under the dosage of 20 mg REs kg(-1) soil (oven-dry mass). The non-observed effect concentration (NOEC) for accumulation of REs in corn seedling with the pot experiment was 1.0 mg REs kg(-1). In the plot experiment, the dose-dependent accumulation was observed at an early stage after application of REs and the NOEC value of 32 mg REs m(-2) was obtained. At harvest, no dose-dependent accumulation of REs was observed in any part of the corn. These results can be confirmed by the fingerprinting analysis based on the differences between La to RE ratios in the REs mixture and in pot or plot soil. We observed that the plant shows no preference on individual RE and the results of fingerprinting indicated clearly the incorporation of exogenous REs in plant tissues, in a similar manner as that observed in the dose-dependent distribution of RE concentrations. The results indicated also a translocation process of REs from plant root to leaf when applied to soil or from leaf to root when applied to leaf. A homeostatic regulation mechanism for excessive uptake of REs in plants is suggested to regulate the concentrations of REs in the plant.

Specific p53 mutations detected in plasma and tumors of hepatocellular carcinoma patients by electrospray ionization mass spectrometry

Hepatocellular carcinoma (HCC), a common cause of cancer deaths worldwide, has several major etiological risk factors, including infection with the hepatitis viruses and exposure to aflatoxin B1. A specific missense mutation resulting from a guanine to thymine transversion at the third position of codon 249 in the p53 tumor suppressor gene has been reported in 10-70% of HCCs from areas of high dietary exposure to aflatoxin B1. Short oligonucleotide mass analysis was compared with DNA sequencing in 25 HCC samples for specific p53 mutations. Mutations were detected in 10 samples by short oligonucleotide mass analysis in agreement with DNA sequencing. Analysis of another 20 plasma and tumor pairs showed 11 tumors containing the specific mutation, and this change was detected in six of the paired plasma samples. Four of the plasma samples had detectable levels of the mutation; however, the tumors were negative, suggesting possible multiple independent HCCs. Ten plasma samples from healthy individuals were all negative. This molecular diagnostic technique has implications for prevention trials and for the early diagnosis of HCC.

Excretion pattern investigation of urinary normal and modified nucleosides of breast cancer patients by RP-HPLC and factor analysis method

Modified nucleosides, formed post-transcriptionally in RNA by a number of modification enzymes, are excreted in abnormal levels in the urine of patients with malignant tumors. To test their usefulness as tumor markers, and to compare them with the conventional tumor markers, a reversed-phase high-performance liquid chromatographic (RP-HPLC) method and a factor analysis method have been used to study the excretion pattern of nucleosides of breast cancer patients. A clear cut differentiation of the breast cancer group and the healthy individuals in two clusters without overlapping was obtained.

Immunolocalization of heat shock protein 70 during reparative dentinogenesis

OBJECTIVE

To investigate the immunolocalization of heat shock protein 70 (hsp 70) during reparative formation and to discuss the role of heat shock response in dental pulp injury and repair.

METHODS

A single cavity was prepared in the mesial surface of the first molars of both maxilla and mandible in Wistar rat. The animals were sacrificed at 3, 15, and 30 days post-operation. After the histological process, the paraffin sections were reacted with monoclonal antibodies against rat hsp 70 using the strept-avidin-biotin-peroxidase complex method.

RESULTS

Immunolocalization demonstrated heavy staining for hsp 70 in normal pulp and at different stages of dental pulp repair. In normal pulp, immunoreactivity was visualized in the odontoblasts and the pulp fibroblast. In the group sacrificed at 3 days, heavy staining was located in the odontoblast process and cytoplasm. After 15 days, the newly formed odontoblast-like cells were strongly stained. At 30 days, the same staining intensity was observed in odontoblast-like cells and in pulp cells. No staining was seen in reparative dentin.

CONCLUSION

These results demonstrated that heat shock protein 70 might play an important role as a molecular chaperone during reparative dentin formation.

The research and development of noncontact 3-D laser dental model measuring and analyzing system

OBJECTIVE

To research and develop a new laser scanning 3-dimensional digitization system for collecting, showing, and measuring the data of dental casts.

MATERIAL AND METHODS

According to the 3-dimensional measuring method, by using 2 pulsate motors to make the synthetic movement of the dental cast, a special semiconductor laser, and 2 special line array CCD, the 3-D data could be found anywhere on the surface of the dental cast. The program, developed with Visual C++ language under the Windows (Windows tm) system, can control the scanner, rebuild the 3-D graphics and measure the data of the dental cast.

RESULTS

The system offers 70 x 70 x 70 mm measurement scope, 0.01 mm resoling power, < 0.1 mm mean deviation, and 25 mins for single cast scanning.

CONCLUSION

The advantages of this system are its precision, simplicity, high efficiency, and wide range of measurements with complete direct view. This system also supplied new information that cannot be found with traditional measurement methods.

Characterization and complementation of a Pichia stipitis mutant unable to grow on D-xylose or L-arabinose

Pichia stipitis CBS 6054 will grow on D-xylose, D-arabinose, and L-arabinose. D-Xylose and L-arabinose are abundant in seed hulls of maize, and their utilization is important in processing grain residues. To elucidate the degradation pathway for L-arabinose, we obtained a mutant, FPL-MY30, that was unable to grow on D-xylose and L-arabinose but that could grow on D-arabinitol. Activity assays of oxidoreductase and pentulokinase enzymes involved in D-xylose, D-arabinose, and L-arabinose pathways indicated that FPL-MY30 is deficient in D-xylitol dehydrogenase (D-XDH), D- and L-arabinitol dehydrogenases, and D-ribitol dehydrogenase. Transforming FPL-MY30 with a gene for xylitol dehydrogenase (PsXYL2), which was cloned from CBS 6054 (GenBank AF127801), restored the D-XDH activity and the capacity for FPL-MY30 to grow on L-arabinose. This suggested that FPL-MY30 is critically deficient in XYL2 and that the D-xylose and L-arabinose metabolic pathways have xylitol as a common intermediate. The capacity for FPL-MY30 to grow on D-arabinitol could proceed through D-ribulose.

[Computerized surgical simulation with 3D reconstruction of upper limbs]

This paper reports our study on how to realize computerized surgical simulation through reconstructing 3D anatomy of upper limbs. CT images and serial sections of upper limbs were matched to reconstruct 3D images. We compiled the computer programs of 3D reconstruction and surgical simulation with borland C++ computer language, and built 3D digital model of anatomic structure of upper limbs. The results showed that all structures reconstructed could be displayed alone, in any group or totally. While operating, we could choose one of three segments of the upper limbs model and operate on any parts and in any direction. The surgical simulation system could be used to design operative schemes, choose the best operative paths, and teach the processes of operations and anatomy. It could run in 586-personal computers.

Effects of delaying puberty on bone mineralization in female rats

The effect of delaying puberty on bone mineralization was studied using female rats as a model. Repeated injections of gonadotrophin-releasing hormone antagonist (GnRHa) were used to suppress the onset of puberty from the age of 6-10 weeks. A group of control female rats was given aqueous solution injections at the same age and for the same duration. The effect of delaying puberty on bone mineralization was examined using dual energy X-ray absorptiometry (DXA) and peripheral quantitative computerized tomography (QCT), both methods being adapted for small animals. Bone mineral parameters were measured at baseline and at the ages of 10, 17 and 24 weeks in total body, femur and spine. Compared to controls, bone mineral content (BMC) and bone mineral density (BMD), as measured by DXA, were significantly decreased in GnRHa-treated rats in total body and femur at 10 and 24 weeks of age (P < 0.05). The results were even more significant after adjusting for weight. After this adjustment, spine BMC and BMD at 10, 17 and 24 weeks were significantly lower in the treatment group (P < 0.05). Trabecular BMD at the distal femur in the GnRHa treated group as measured by peripheral QCT was significantly lower (P < 0.05). However, cortical bone in the mid-femur had higher BMD, concurrent with lower cortical thickness in the treatment group. In conclusion, a delay in the onset of sexual maturation may cause prolonged, possibly irreversible defect in bone mineralization.

[Epidemiological aspects of the genotype of hepatitis C virus]

OBJECTIVE

To research the epidemiological characteristics of genotype of hepatitis C virus.

METHODS

107 HCV isolates from 7 cities in southern, northern and northeast of China were analyzed using PCR and second generation line probe assay (INNO-LiPA).

RESULTS

The analysis of HCV genotypes showed that: 1. HCV l b was the common genotype (83 17%), however the frequency of genotype l b in northeast (72.22%) was lower than northern (87.65%, P <0.01), and the frequency of the genotype 2 was in low level (6.86%). The rate of coinfection with l b and other genotype was 10.29%. 2. The rate of infection with genotype l b in female patients was higher (93.61%) than that in male (75.0%) showing statistical significance (P <0.01). 3. In three age groups (< 30, 30 - 49 and > 50 years old) the rates of infection with genotype l b were 77.77%, 83.92% and 90.90%, respectively. 4. The detection rates of genotype l b in patients with infection period > 10 years and <10 years were 100% and 80.43% respectively (P <0.01).

CONCLUSIONS

There are some relationship between HCV genotype and HCV geographic distribution, sex, age and infection period of patients.

Multiple types of calcium signals are associated with cell division in zebrafish embryo

Recent studies suggested that a Ca(2+) signal is involved in the regulation of cell division. For example, using a confocal imaging technique, we have shown that a localized Ca(2+) elevation was clearly associated with the onset of cytokinesis in zebrafish embryo [Chang and Meng (1995) J. Cell Biol. 131:1539-1545]. This finding was later confirmed in studies using aequorin as a Ca(2+) probe. Here, we used a 4-D confocal measurement technique to further characterize the properties of the Ca(2+) signal associated with cell division. We found evidence that there were three types of Ca(2+) signals associated with different stages of cell cleavage in embryonic cell. The first type was repetitive Ca(2+) spikes that emerged several minutes before the first cell cleavage began. These Ca(2+) spikes were first distributed broadly over the central region of the blastodisc and then gradually localized in the equatorial region; they appeared to play the role of determining the position of the first cleavage plane. The second type was a calcium wave that propagated along the cleavage furrow and appeared to guide the furrow extension during the progression of cytokinesis. The third type was a group of post-cleavage calcium spikes that appeared to be responsible for furrow deepening and maintenance of the contractile band. When this type of Ca(2+) transient was blocked by injecting BAPTA or heparin, cell cleavage regressed and the structure of the contractile band could no longer be maintained.

[Study on human leucocyte antigen-DQ region gene polymorphism in cases of habitual abortion with anticardiolipin antibody]

OBJECTIVE

To investigate the relationship between human leucocyte antigen(HLA)-DQ region gene polymorphism and habitual abortion with anticardiolipin antibody(ACL).

METHODS

Polymerase chain reaction-restrictive fragment length polymorphism (PCR-RFLP) was used to type HLA-DQA1 and HLA-DQB1 alleles in 30 cases of habitual abortion with anticardiolipin antibody and 90 women with normal pregnancy history.

RESULTS

The frequency of DQB1 * 0303 was found to be significantly higher in ACL(+) habitual abortion group (33.3%) than those in normal control group (P < 0.05). Whereas, there was no significant difference found not only in frequency of other DQB1 alleles, but also in frequency of DQA1 alleles and DQA1-DQB1 haplotypes between two groups.

CONCLUSION

The results show an association between ACL(+) habitual abortion and HLA-DQB1 * 0303, which suggest DQB1 * 0303 may be susceptible gene to ACL(+) habitual abortion.

Validation of a new technique to detect malingering of cognitive symptoms: the b Test

We administered the b Test, a new measure to identify malingering requiring recognition of overlearned information, to 34 suspected malingerers and to 161 subjects in various clinical groups (moderate to severe head injury, elderly depressed, learning disability, schizophrenia, right and left CVA, and elderly normals). Comparisons of groups revealed more commission and omission errors in the suspected malingerers relative to all groups except the right stroke patients. In addition, suspected malingerers took longer to complete the task than all groups except right and left stroke patients and normal elderly. A cutoff of >2 commission errors produced a sensitivity of 76.5% and specificity for all comparison groups combined of 82.6%. Lower sensitivity rates were documented for omissions (58.8 using cutoff of >40) and time (57.6% using cutoff of >12 minutes), but specificity remained high at 85.1% and 83.9%, respectively. Thus, the b Test shows considerable potential as a malingering detection tool.

Application of a mid-infrared fiber bundle in remote measurement of gas concentrations in a chemical vapor deposition chamber

A fiber bundle has been designed for measurement of gas concentrations in a chemical vapor deposition (CVD) chamber. The bundle is broadband, covering the spectrum range from 500 to 6000 cm(-1). Using this bundle, we have designed Fourier Transform infrared (FTIR) sampling configurations with reduced beam divergence (from 0.4 to 0.1 rad) and focal spot diameters (from 12 to 4 mm). The FTIR spectrum of tetraethoxysilane vapors in a CVD chamber was determined with the bundle and modified SAM connectors. An ellipsoid reflector was designed that yielded improved signal-to-noise ratios (SNR's) in the fiber-based spectra by a factor of 2. The incorporation of this reflector in spectrometers by use of the fiber bundle has the potential to reduce the sampling times for spectra while retaining acceptable SNR's.

[The research of a multimedia consultative system for prosthodontics]

OBJECTIVE

To study how to develop the consultative multimedia system for prosthodontics facilitating the communication between the dentists and patients, using multimedia techniques.

METHODS

The Founder Author Tools V2.1 was used to develop the consultative system in the Pwin95/98 environment. Many forms (such as the articles, pictures, sound and video) of the prosthodontic knowledge were edited in this system.

RESULTS

The consultative multimedia system for prosthodontics was developed, and there were three main parts of the system: (1) the background of medical departments, (2) introductions of the medical specialists (including their photos and working time), (3) introducing the common acknowledge of prosthodontics.

CONCLUSION

The visualization of the prosthodontic problems consulted by patients frequently can facilitate the communication between the dentists and patients and spare visit time. This system are welcome by the patients.

Interspecies comparison and role of human cytochrome P450 and flavin-containing monooxygenase in hepatic metabolism of L-775,606, a potent 5-HT(1D) receptor agonist

1. Quantitative species differences and human liver enzymes involved in the metabolism of L-775,606, a potent and selective 5-HT1D receptor agonist developed for the acute treatment of migraine headache, have been investigated in vitro. 2. In human, monkey, dog and rat liver microsomes, formation of the hydroxylated M1 and the N-dealkylated M2 was mediated by enzyme(s) of high-affinity (apparent Km approximately 1-6 microM), and that of the two N-oxide isomers (M3) was catalysed by those of low affinity (apparent Km approximately 50-110 microM). In dog, M3 constituted a major pathway (approximately 40%), whereas in all other species it was a minor metabolite (< 5%). 3. In human liver microsomes, a marked inhibition (> or =80%) of M1 and M2 formation was observed by SKF525-A, troleandomycin, ketoconazole and anti-CYP3A antibodies, whereas the inhibition was modest (approximately 20-40%) with quercetin. Of seven cDNA-expressed human P450 tested, only CYP3A4 and CYP2C8 were capable of oxidizing L-775,606, resulting primarily in M1 and M2. However, CYP3A4 possessed much higher affinity (> or = 20-fold) and much higher intrinsic activity (> 100-fold) than CYP2C8. 4. In contrast, N-oxidation was not inhibited by any inhibitors of P450 tested, but rather was reduced significantly by heat treatment and methimazole, and was increased substantially with an incubation pH>7.4. Human flavin-containing monooxygenase form 3 (FMO3) catalysed exclusively the N-oxidation to M3, with apparent Km and optimum pH comparable with those observed in human liver microsomes. 5. These results demonstrated quantitative interspecies differences in the metabolism of L-775,606. In human, metabolism of L-775,606 to the principal metabolites, M1 and M2, was mediated primarily by CYP3A4 with minimal contribution from CYP2C8, whereas the minor N-oxidative pathway was catalysed mainly by FMO3.

Insights into the structure and substrate interactions of the P-glycoprotein multidrug transporter from spectroscopic studies

The P-glycoprotein multidrug transporter is a 170-kDa efflux pump which exports a diverse group of natural products, chemotherapeutic drugs, and hydrophobic peptides across the plasma membrane, driven by ATP hydrolysis. The transporter has been proposed to interact with its drug substrates within the membrane environment; however, much remains to be learned about the nature and number of the drug binding site(s). The two nucleotide binding domains are responsible for ATP binding and hydrolysis, which is coupled to drug movement across the membrane. In recent years, P-glycoprotein has been purified and functionally reconstituted in amounts large enough to allow biophysical studies. The use of spectroscopic techniques has led to insights into both its secondary and tertiary structure, and its interaction with nucleotides and drugs. In this review, we will summarise what has been learned by application to purified P-glycoprotein of fluorescence spectroscopy, circular dichroism spectroscopy and infra-red spectroscopy.

[A study of dental cast by using 3D laser non-contact measurement and analysis]

OBJECTIVE

To research and develop a new scanning 3-D digitization system for noncontact measuring of dental cast.

METHODS

By using two pulsate motor to make the synthetic movement of the dental cast, a special semiconductor laser and two special line-array CCD, the 3D coordinate could be gotten from the surface of the dental cast in any where. The program which is developed by Visual C++ language and run under the Windows surroundings can control the scanner, rebuild the 3D graphics and measure the coordinate of the dental cast.

RESULTS

The system offers 70 mm x 70 mm x 70 mm measurement scope, 0.01 mm resoling power < 0.1 mm mean deviation, 25 mins for single cast scanning.

CONCLUSION

This system provides many advantages such as in precision, simplicity, high efficiency, and wide range of measurement contents with complete direct view. It also supplied us some new functions which can not be done with traditional way of measurement.

Reversed-phase high-performance liquid chromatographic investigation of urinary normal and modified nucleosides of cancer patients

Post-transcriptional modifications in RNA give rise to free modified ribonucleosides circulating in the blood stream and excreted in urine. Due to their abnormal levels in conjunction with several tumor diseases, they have been suggested as possible tumor markers. The developed RP-HPLC method has been applied to analyze the urinary nucleosides in 34 urinary samples from 15 kinds of cancer patients. The statistical analyses showed the urinary nucleoside excretion, especially modified nucleoside levels, in cancer patients were significantly higher than those in normal healthy volunteers. Factor analysis was used to classify the patients with cancer and normal healthy humans. It was found that using 15 urinary nucleoside levels or only five modified nucleoside levels as data vectors the factor analysis plot displayed two almost separate clusters representing each group.

Interaction of the P-glycoprotein multidrug transporter (MDR1) with high affinity peptide chemosensitizers in isolated membranes, reconstituted systems, and intact cells

P-glycoprotein-mediated multidrug resistance can be reversed by the action of a group of compounds known as chemosensitizers. The interactions with P-glycoprotein of two novel hydrophobic peptide chemosensitizers (reversins 121 and 205) have been studied in model systems in vitro, and in a variety of MDR1-expressing intact tumor cells. The reversins bound to purified P-glycoprotein with high affinity (77-154 nM), as assessed by a quenching assay using fluorescently labeled purified protein. The peptides modulated P-glycoprotein ATPase activity in Sf9 insect cell membranes expressing human MDR1, plasma membrane vesicles from multidrug-resistant cells, and reconstituted proteoliposomes. Both peptides induced a large stimulation of ATPase activity; however, higher concentrations, especially of reversin 205, led to inhibition. This pattern was different from that of simple linear peptides, and resembled that of chemosensitizers such as verapamil. In both membrane vesicles and reconstituted proteoliposomes, 1-2 microM reversins were more effective than cyclosporin A at blocking colchicine transport. Reversin 121 and reversin 205 restored the uptake of [3H]daunorubicin and rhodamine 123 in MDR1-expressing cells to the level observed in the drug-sensitive parent cell lines, and also effectively inhibited the extrusion of calcein acetoxymethyl ester from intact cells. In cytotoxicity assays, reversin 121 and reversin 205 eliminated the resistance of MDR1-expressing tumor cells against MDR1-substrate anticancer drugs, and they had no toxic effects in MDR1-negative control cells. We suggest that peptides of the reversin type interact with the MDR1 protein with high affinity and specificity, and thus they may be good candidates for the development of MDR1-modulating agents to sensitize drug resistance in cancer.

Increased risk of hepatocellular carcinoma in male hepatitis B surface antigen carriers with chronic hepatitis who have detectable urinary aflatoxin metabolite M1

We followed 145 men with chronic hepatitis B virus (HBV) hepatitis for 10 years to determine whether exposure to aflatoxin, or concomitant exposure to hepatitis C virus (HCV), or family history of hepatocellular carcinoma (HCC) increased the risk of developing HCC. We collected 8 monthly urine samples before beginning follow-up and pooled them to detect aflatoxin metabolite M1 (AFM1). AFM1 was detected in 78 (54%) of the subjects. The risk of HCC was increased 3.3-fold (with a 95% confidence interval of 1.2-8.7) in those with detectable AFM1 (above 3.6 ng/L). This relative risk was adjusted for age and for HCV status. The attributable risk from exposure to detectable AFM1 was 0.553 (0.087, 0.94). The relative risk of fatal cirrhosis for those with elevated AFM1 was 2.8 (0.6, 14.3), and the odds of having a persistently elevated alanine transaminase (ALT) were 2.5-fold greater in those with detectable AFM1 (P =.007). Concomitant infection with HCV increased the risk of HCC 5.8-fold (2. 0-17), adjusted for age and AFM1 status. A family history of HCC increased the risk of HCC 5.6-fold, adjusted for age and AFM1. Four men with detectable AFM1 and HCC all had missense mutation in codon 249 of the p53 gene in cancer tissues. This study shows that exposure to AFM1 can account for a substantial part of the risk of HCC in men with chronic HBV hepatitis and adds importantly to the evidence that HCV and family history of HCC increase the risk of HCC in men with chronic HBV hepatitis.

Distribution of retroviral vectors and vector producer cells using two routes of administration in rats

The clinical use of retroviral vector producer cells (VPCs) to deliver retroviral vectors efficiently to target cells has been investigated as a method to increase efficiency of gene delivery, presumably as a result of continued vector production in vivo. Studies were conducted in rats to evaluate the distribution of vector to distal organs and tissues as measured by transduction. Rats were treated with two doses of VPCs using two routes of administration: (1) subcutaneous injection, chosen to maximize both the dose and exposure of animals, thereby enabling identification of potential target organs under worst-case conditions; and (2) direct injection into brain parenchyma, chosen to mimic the intended clinical route of administration and provide an estimate of risk to patients receiving this therapy. Twelve organs or tissues were collected 7 days after administration of VPCs and analyzed by PCR for the presence of vector and vector producer cell sequences. Vector was detected most frequently at the site of injection by either route of administration. Less frequently, vector was detected in draining lymph nodes at the higher dose only using either route of injection. Single specimens of lung and contralateral skin were positive for vector following subcutaneous administration only. Vector was detected in gonadal tissue from a single low-dose male following subcutaneous administration, but this finding was not reproduced in any high-dose male or any males injected intracerebrally. In contrast, VPCs were detected only at the site of administration. The frequency of detection of VPCs 7 days after administration was higher when rats were injected by the intracerebral route. Based on these studies, gene transfer to distal organs or gonadal tissue following intracerebral administration of VPCs is not considered to be a risk to patients undergoing retroviral vector gene therapy for the treatment of brain cancer (glioblastoma multiforme; GBM).

[Operative results of tethered cord syndrome]

OBJECTIVE

To evaluate the treatment results of 22 cases of spinal tethered cord syndrome (TCS) using microneurosurgical technique.

METHODS

Form 1994 to 1997, 22 cases of TCS verified by MRI were treated. All patients'tips of conus were below L(2) vertebra shown by MRI. In this group, 4 cases had lipid disease in the sacral canal, 5 piloidal sinus, and 13 thick filum. The patients were operated on using linear incision. The incision included the terminal conus and the whole filum. Under the microscope, the adhesions of the caudal equine were separated and the filum was found out. The caudal equine was well combed. Lipoma and piloidal sinus were removed totally or partially. Loosening the spinal conus and repairing the dural matter prevented re-adhesion and re-tether.

RESULTS

Follow-up (0.5 - 3 years) showed that all of the patients were recovered in different levels.

CONCLUSIONS

TCS should be found as early as possible and treated under the microsurgical technique.

[Gas chromatographic method for the analysis of polychlorinated biphenyls in pine needles]

Polychlorinated biphenyls (PCBs) are a class of 209 chemical compounds, in which 1-10 chlorine atoms are attached to a biphenyl molecule. PCBs are members of halogenated aromatic group of environmental pollutants that have been identified worldwide in diverse environmental matrices. PCBs in air, soils, sediment, water, transformer oils and other environmental matrices have been determined in the past years. In this work a method for routine analysis of PCBs in pine needles has been developed. First, extractions were carried out in Soxhlet apparatus with n-hexane as solvent. Then, a silica gel chromatographic column was applied to pretreat the pine needle samples. The reference standard used was clophen 50. The recovery was about 90%, so the feasibility and reliability were assured. After the analysis of PCBs in pine needle samples from four different regions, the distribution of PCBs in environment can be discussed and monitored. In this method, a Shimadzu GC-7A gas chromatograph equipped with a 63Ni electron capture detector was used for the analysis of PCBs. From the results, we can see the PCB pollution in different regions. So evaluation of air pollution level through foliage data is feasible. The sample preparation and analytical method mentioned in this paper is reliable and simple.

[Apoptosis of human gastric cancer cells induced by bcl-2 antisense oligodeoxynucleotides]

OBJECTIVE

To study the regulation of bcl-2 gene expression and induction of apoptosis by bcl-2 antisense oligodeoxynucleotides (AS-ODN) on human gastric cancer cell line BGC-823 in vitro.

METHODS

Two bcl-2 AS-ODNs were synthesized, one covering the initiation sequence of translation of bcl-2 mRNA (AS-ODN1) and the other covering the protein coding region (AS-ODN2). BGC-823 cells in logarithmic phase of growth were cultured in the presence of free or liposome (DOTAP)-encapsulated AS-ODN. Cell growth was assessed by MTT method. The expression of bcl-2 at mRNA and protein levels was examined by RT-PCR and flow cytometry, respectively. Electron microscopy and flow cytometry were used to demonstrate apoptotic changes in AS-ODN-treated cells.

RESULTS

Both AS-ODNs inhibited proliferation of BGC-823 cells. The inhibitory activity of AS-ODN2 was stronger than that of AS-ODN1. AS-ODNs encapsulated in liposome led to more marked inhibition of cell growth than free AS-ODNs. Both AS-ODNs reduced bcl-2 expression of BGC-823 cells at mRNA and protein levels. Apoptosis of BGC-823 cells were demonstrated by the appearance of apoptotic bodies, chromatin condensation and pre-G1 peak on flow cytometric analysis.

CONCLUSION

Antisense oligodeoxynucleotide of bcl-2 decreases bcl-2 gene expression and induces apoptosis of human gastric cancer cells in vitro.

Dynamic redistribution of calmodulin in HeLa cells during cell division as revealed by a GFP-calmodulin fusion protein technique

It has been suggested by many studies that Ca2+ signaling plays an important role in regulating key steps in cell division. In order to study the down stream components of calcium signaling, we have fused the gene of calmodulin (CaM) with that of green fluorescent protein (GFP) and expressed it in HeLa cells. The GFP-CaM protein was found to have similar biochemical properties as the wild-type CaM, and its distribution was also similar to that of the endogenous CaM. Using this GFP-tagged CaM as a probe, we have conducted a detailed examination of the spatial- and temporal-dependent redistribution of calmodulin in living mammalian cells during cell division. Our major findings are: (1) high density of CaM was found to distribute in two sub-cellular locations during mitosis; one fraction was concentrated in the spindle poles, while the other was concentrated in the sub-membrane region around the cell. (2) The sub-membrane fraction of CaM became aggregated at the equatorial region where the cleavage furrow was about to form. The timing of this localized aggregation of CaM was closely associated with the onset of cytokinesis. (3) Using a TA-CaM probe, we found that the sub-membrane fraction of CaM near the cleavage furrow was selectively activated during cell division. (4) When we injected a CaM-specific inhibitory peptide into early anaphase cells, cytokinesis was either blocked or severely delayed. These findings suggest that, in addition to Ca2+ ion, CaM may represent a second signal that can also play an active role in determining the positioning and timing of the cleavage furrow formation.

Molecular evaluation of biopsy and autopsy specimens from patients receiving in vivo retroviral gene therapy

We used the polymerase chain reaction (PCR) to assay for the presence of retroviral vector and replication-competent retrovirus (RCR) in autopsy and biopsy specimens from patients who received inoculations of retroviral vector producer cells (VPCs) into brain tumors or apparently normal tissues surrounding resected tumors. The PCR assays were capable of detecting 1 or more proviral copies of vector or RCR in 500,000 cells. Of 113 patients treated in clinical trials between 1994 and 1997, autopsy specimens were available from 32 patients. Brain tumor biopsies were also available from 24 patients. A total of 346 specimens was analyzed. Vector DNA was detected in 55% of tumor samples and 22% of brain samples obtained from resection margins. In contrast, most of the nonbrain tissues were negative for vector DNA; only low levels (<0.03%) of vector sequence were detected in 6 of 240 (2.5%) nonbrain tissues. Vector DNA was not detected in gonadal tissues from 12 men and 10 women. More importantly, RCR was not detected in any of the 134 biopsy and autopsy tissues tested, including all brain tumor, brain, and gonadal specimens. These results comprise the largest data set on molecular analysis of autopsy specimens from patients receiving retroviral gene therapy and indicate that distribution of retroviral vectors following injection of high doses of VPCs is limited to the site of inoculation.

[Development of column switching systems in industrial gas chromatography]

According to the home-made requirement of column switching systems in 23 industrial gas chromatographs in 300,000 Tons of olefin plant, based on the research work of the expert system on gas chromatography and movement laws of compounds of interest in columns, the suitable stationary phases were defined, and the column switching systems were designed by using combined cutting techniques which consist of backflushing, fore-flushing and heart cutting, and by controlling column lengths, flows, flow directions and temperatures. The practical applications showed the column systems satisfy the on-line monitoring requirement of the production process and can be used continually for 1-3 years.

Metabolic interactions between mibefradil and HMG-CoA reductase inhibitors: an in vitro investigation with human liver preparations

AIMS

To determine the effects of mibefradil on the nletabolism in human liver microsomal preparations of the HMG-CoA reductase inhibitors simvastatin, lovastatin, atorvastatin, cerivastatin and fluvastatin.

METHODS

Metabolism of the above five statins (0.5, 5 or 10 microM), as well as of specific CYP3A4/5 and CYP2C8/9 marker substrates, was examined in human liver microsomal preparations in the presence and absence of mibefradil (0.1-50 microM).

RESULTS

Mibefradil inhibited, in a concentration-dependent fashion, the metabolism of the four statins (simvastatin, lovastatin, atorvastatin and cerivastatin) known to be substrates for CYP3A. The potency of inhibition was such that the IC50 values (<1 microM) for inhibition of all of the CYP3A substrates fell within the therapeutic plasma concentrations of mibefradil, and was comparable with that of ketoconazole. However, the inhibition by mibefradil, unlike that of ketoconazole, was at least in part mechanism-based. Based on the kinetics of its inhibition of hepatic testosterone 6beta-hydroxylase activity, mibefradil was judged to be a powerful mechanism-based inhibitor of CYP3A4/5, with values for Kinactivation, Ki and partition ratio (moles of mibefradil metabolized per moles of enzyme inactivated) of 0.4 min(-1), 2.3 microM and 1.7, respectively. In contrast to the results with substrates of CYP3A, metabolism of fluvastatin, a substrate of CYP2C8/9, and the hydroxylation of tolbutamide, a functional probe for CYP2C8/9, were not inhibited by mibefradil.

CONCLUSION

Mibefradil, at therapeutically relevant concentrations, strongly suppressed the metabolism in human liver microsomes of simvastatin, lovastatin, atorvastatin and cerivastatin through its inhibitory effects on CYP3A4/5, while the effects of mibefradil on fluvastatin, a substrate for CYP2C8/9, were minimal in this system. Since mibefradil is a potent mechanism-based inhibitor of CYP3A4/5, it is anticipated that clinically significant drug-drug interactions will likely ensue when mibefradil is coadministered with agents which are cleared primarily by CYP3A-mediated pathways.

Two approaches for determining the urinary excretion patterns of nucleosides--HPLC and CE

Cancer patients excrete in their urine increased amounts of modified purines and pyrimidines. These modified mucleosides are primary constituents of RNA and are synthesized at the macromolecular level. When RNA is catabolized, most of these modified nucleosides cannot be reutilized; consequently, they are excreted. Due to their increased urinary excretion in conjunction with altered RNA turnover in carcinogenesis, they have been proposed as tumour markers. We developed both reversed-phase high performance liquid chromatographic and capillary electrophoretic approaches to determine normal and modified nucleosides in urine. Data obtained with CE are in good accordance with those from HPLC. The reference excretion levels of urinary nucleosides from healthy volunteers were established, and elevated ones of modified nucleosides from 34 patients with different kinds of cancer were observed. The developed methods are suitable for the analysis of large series of samples for clinical studies.

[Selectivity tuning in multi-binary eluents for reversed-phase liquid chromatography (RPLC)]

In this article, the retention equation and the relationship between retention parameters and the parameters of molecular structure deduced from statistical thermodynamics in RPLC have been used to explain the difference of selectivity towards a particular species of compounds polycyclic aromatic hydrocarbons (PAHs). Methanol/water, acetonitrile/water and isopropanol/acetonitrile have been provided in advance, then the retention behaviors of sixteen PAHs under three binary solvent systems have been investigated. It is found that each pair of binary solvents of methanol/water, acetonitrile/water and isopropanol/acetonitrile has its own unique selectivity. The best selectivity obtained for acenaphthene and fluorene is methanol/water system for fluoranthene and pyrene is acetonitrile/water, and for benzo[g,h,i]perylene and dibenzo[a,h]anthracene is isopropanol/acetonitrile. So a three-stepwise gradient elution of multi-binary mobile phase can be chosen for separation of 16 PAHs.

Modern woman medical education in China after the introduction of western medicine

In 1879, Nanhua (Southern China) Medical School, the earliest school for western medical professionals in China, first admitted women to study medicine in separate class. In 1885, Yamei King became the first woman conferred a medical doctor degree from the US. The first woman medical school, the Canton Woman Medical School, began to enroll students. In 1933, of the 3655 students in the 28 medical schools, 619 were female, representing 16.94% of the total. Among these schools, 2 were exclusively for females, 3 for males, the remaining 23 for both sexes. In 1934, special committee for nurse and midwife were set up in the medical education committee in Ministry of Education. Up to this year, there were 2 state - run, 10 province - run and 206 private - nurse's schools, and 21 schools for midwife training.

Real time detection of DNA.RNA hybridization in living cells

Demonstrating hybridization between an antisense oligodeoxynucleotide and its mRNA target has proven to be extremely difficult in living cells. To address this fundamental problem in antisense research, we synthesized "molecular beacon" (MB) reporter oligodeoxynucleotides with matched fluorescent donor and acceptor chromophores on their 5' and 3' ends. In the absence of a complementary nucleic acid strand, the MB remains in a stem-loop conformation where fluorescence resonance energy transfer prevents signal emission. On hybridization with a complementary sequence, the stem-loop structure opens increasing the physical distance between the donor and acceptor moieties thereby reducing fluorescence resonance energy transfer and allowing a detectable signal to be emitted when the beacon is excited by light of the appropriate wavelength. Solution hybridization studies revealed that in the presence of a complementary strand targeted MB could yield up to a 60-fold increase in fluorescence intensity in comparison to control MB. By using a fluorescence microscope fitted with UV fluoride lenses, the detection limit of preformed MB/target sequence duplexes microinjected into cells was found to be >/=1 x 10(-1) ag of MB, or approximately 10 molecules of mRNA. On the basis of this exquisite sensitivity, real-time detection of MB/target mRNA hybridization in living cells was attempted by microinjecting MB targeted to the vav protooncogene, or control MB, into K562 human leukemia cells. Within 15 min, confocal microscopy revealed fluorescence in cells injected with targeted, but not control, MB. These studies suggest that real-time visualization and localization of oligonucleotide/mRNA interactions is now possible. MB could find utility in studying RNA processing, trafficking, and folding in living cells. We hypothesize that MB may also prove useful for finding targetable mRNA sequence under physiologic conditions.

Linear and cyclic peptides as substrates and modulators of P-glycoprotein: peptide binding and effects on drug transport and accumulation

One cause of multidrug resistance (MDR) in human cancers is the overexpression of the P-glycoprotein multidrug transporter, a member of the ABC superfamily of membrane proteins. Natural products and chemotherapeutic drugs are pumped out of the cell by P-glycoprotein in an ATP-dependent fashion. There is growing evidence that many hydrophobic peptides are also P-glycoprotein substrates. With the use of a fluorescence-quenching assay, we have shown that some linear and cyclic hydrophobic peptides interact with P-glycoprotein, whereas others do not. The measured values of the quenching constant, Kq, for interaction of peptides with P-glycoprotein ranged from 200 nM for cyclosporine A to 138 microM for the tripeptide N-acetyl-leucyl-leucyl-norleucinal. Peptides that interacted with P-glycoprotein in the fluorescence assay also blocked colchicine transport into plasma membrane vesicles from MDR cells. The values of Dm, the peptide concentration causing 50% inhibition of drug uptake, were highly correlated with the values of Kq, over three orders of magnitude. The P-glycoprotein ATPase stimulation/inhibition profile of the peptides was not helpful in making a quantitative assessment of the ability of a peptide to interact with P-glycoprotein or to block drug transport. Some hydrophobic peptides were able to restore accumulation in MDR cells of the chemotherapeutic drug daunorubicin and the fluorescent dye rhodamine 123 to the levels observed in the drug-sensitive parent. Peptides that interacted with P-glycoprotein also displayed a relatively low overall toxicity to intact MDR cells, and inhibited drug transport at concentrations below the toxic range. Hydrophobic peptides should be given serious consideration for development as clinical chemosensitizing agents.

[Hepatitis B virus infection and aflatoxin exposure in the development of primary liver cancer]

OBJECTIVE

To investigate the role of hepatitis B Virus (HBV) infection and aflatoxin (AF) exposure in the development of primary liver cancer (PLC).

METHODS

A 10-year prospective case-control study was carried out in 737 HBsAg carriers and 699 HBsAg negative cases, and the aflatoxin B1 albumin adducts (AFB1-Alb) were detected in the serum of the cohort including 30 HBsAg postive cases and 150 control individuals according to the case-control study model (ratio 1:5) at random in the high prevalance area of PLC.

RESULTS

The average year-incidence rate was significantly higher in the HBsAg postive group (824.13/100,000) than in the control group (70.97/100,000, RR = 11.61). There was no significant difference in the incidence rate of other tumors between the two groups (P > 0.05). The serum positive rate of AFB1-Alb was significantly higher in the PLC group (76.67%) than in the control group (48.67%, OR = 3.47), and the serum concentration of AFB1-Alb was also significantly higher in the PLC group than in the control group (P < 0.01).

CONCLUSION

HBV infection and AF exposure are important etiological factors in the development of PLC and both result in carcinogenic synergy.

Arabidopsis SKP1, a homologue of a cell cycle regulator gene, is predominantly expressed in meristematic cells

The yeast SKP1 gene and its human homolog p19skp1 encode a kinetochore protein required for cell cycle progression at both the DNA synthesis and mitosis phases of the cell cycle. In orchids we identified a cDNA (O 108) that is expressed in early stages of ovule development and is homologous to the yeast SKP1. Based on the orchid O 108 cDNA clone, we identified and characterized an Arabidopsis thaliana (L.) Heynh. cDNA designated ATskp1 that also has high sequence similarity to yeast SKP1. The Arabidopsis ATskp1 is a single-copy gene that mapped to chromosome 1. The expression of the ATskp1 gene was highly correlated with meristem activity in that its mRNA accumulated in all of the plant meristems including the vegetative shoot meristem, inflorescence and floral meristems, root meristem, and in the leaf and floral organ primordia. In addition, ATskp1 was also highly expressed in the dividing cells of the developing embryo, and in other cells that become multinucleate or undergo endoreplication events such as the endosperm free nuclei, the tapetum and the endothelium. Based on its spatial pattern of expression, ATskp1 is a marker for cells undergoing division and may be required for meristem activity.

Cloning and disruption of the beta-isopropylmalate dehydrogenase gene (LEU2) of Pichia stipitis with URA3 and recovery of the double auxotroph

Transformation of Pichia stipitis is required to advance genetic studies and development of xylose metabolism in this yeast. To this end, we used P. stipitis URA3 (PsURA3) to disrupt P. stipitis LEU2 in a P. stipitis ura3 mutant. A highly fermentative P. stipitis mutant (FPL-DX26) was selected for resistance to 5'-fluoroorotic acid to obtain P. stipitis FPL-UC7 (ura3-3). A URA3:lacZ "pop-out" cassette was constructed containing PsURA3 flanked by direct repeats from segments of the lacZ reading frame. The P. stipitis LEU2 gene (PsLEU2) was cloned from a P. stipitis CBS 6054 genomic library through homology to Saccharomyces cerevisiae LEU2, and a disruption cassette was constructed by replacing the PsLEU2 reading sequence with the PsURA3:lacZ cassette. FPL-UC7 (ura3-3) was transformed with the disruption cassette, and a site-specific integrant was identified by selecting for the Leu- Ura+ phenotype. The ura3 marker was recovered from this strain by plating cells onto 5'-fluoroorotate and screening for spontaneous URA3 deletion mutants. Excision of the flanked PsURA3 gene resulted in the Leu- Ura- phenotype. The double auxotrophs are stable and can be transformed at a high frequency by PsLEU2 or PsURA3 carried on autonomous-replication-sequence-based plasmids.