Effect of oxidation of low-density lipoprotein on drug binding affinity studied by high performance frontal analysis-capillary electrophoresis

The effect of oxidation of low-density lipoprotein (LDL) on the enantioselective drug binding affinity was investigated using high performance frontal analysis--capillary electrophoresis (HPFA-CE). Verapamil and nilvadipine enantiomers were used as the chiral model drugs. LDL was oxidized with copper sulfate for 0, 0.5, 1, 2, and 12 h at 37 degrees C. The HPFA-CE method enabled microdetermination of unbound drug concentrations in native and oxidized LDL solutions. It was found that the bindings between LDL and the model drugs were not enantioselective at any oxidation stage. The total binding affinity (nK) between LDL and verapamil enantiomers was increased by 3.3-, 4.6-, 7.0-, and 19-fold after 0.5, 1, 2, and 12 h oxidation, respectively, whereas the nK value between nilvadipine and LDLwas increased by 1.3-, 1.4-, 1.4-, and 1.7-fold in the same reaction times, respectively. These results indicate that the LDL oxidation enhances the drug binding affinity, and the affinity of verapamil is increased more sensitively than that of nilvadipine. The nK value of each model drug increased steeply after the first 2 h oxidation, followed by the gradual increase after the next 10 h oxidation. It is considered that the net increase in the negative charges and/or the formation of hydroperoxides in the first 2 h oxidation enhances the drug-LDL binding more significantly than the formation of aldehydes or Schiff bases in the following 10 h oxidation.

[Clinical analysis of nosocomial infection of extended spectrum beta-lactamase-producing bacteria]

OBJECTIVE

To investigate the clinical characteristics of nosocomial infection of extended spectrum beta-lactamase(ESBL)- producing bacteria.

METHODS

The data of 50 cases of ESBL(+) E. coli and K. pneumonia from January to November 1999 in Peking Union Medical Hospital were analysed; 45 cases of ESBL (-) infection were randomly selected as controls. t-test and chi-square tests were used for statistical analysis.

RESULTS

Long time hospitalization and use of the third generation cephalosporins were risk factors for ESBL(+) pathogen infection(P < 0.02); the prevalence of ESBL(+) bacteria infection in abdominal and pelvic cavity was higher than that of ESBL(-) bacteria(P < 0.02); the outcome of properly treated group(sensitive antibiotics were used within 72 hours) was much better than improperly treated group. All ESBL(+) bacteria were sensitive to imipenam, the resistance rate of ESBL(+) bacteria to cefmetazole, amikacin and piperacillin/tazobactam was low; the in vitro activity of ceftazidim to ESBL(+) bacteria was high but the in vivo activity is still under study.

CONCLUSION

The mortality of ESBL(+) bacteria infection was high; the outcome would be improved if sensitive antibiotics were chosen as soon as the diagnosis was made.

Neutralizing monoclonal antibodies to hepatocyte growth factor/scatter factor (HGF/SF) display antitumor activity in animal models

The hepatocyte growth factor (HGF/SF) receptor, Met, regulates mitogenesis, motility, and morphogenesis in a cell type-dependent fashion. Activation of Met via autocrine, paracrine, or mutational mechanisms can lead to tumorigenesis and metastasis and numerous studies have linked inappropriate expression of this ligand-receptor pair to most types of human solid tumors. To prepare mAbs to human HGF/SF, mice were immunized with native and denatured preparations of the ligand. Recloned mAbs were tested in vitro for blocking activity against scattering and branching morphogenesis. Our results show that no single mAb was capable of neutralizing the in vitro activity of HGF/SF, and that the ligand possesses a minimum of three epitopes that must be blocked to prevent Met tyrosine kinase activation. In vivo, the neutralizing mAb combination inhibited s.c. growth in athymic nu/nu mice of tumors dependent on an autocrine Met-HGF/SF loop. Importantly, growth of human glioblastoma multiforme xenografts expressing Met and HGF/SF were markedly reduced in the presence of HGF/SF-neutralizing mAbs. These results suggest interrupting autocrine and/or paracrine Met-HGF/SF signaling in tumors dependent on this pathway is a possible intervention strategy.

Muscle-derived cell transplantation and differentiation into lower urinary tract smooth muscle

OBJECTIVES

To explore the feasibility of primary skeletal muscle-derived cell (MDC)-based tissue engineering and gene transfer into the lower urinary tract and to explore whether the injected primary skeletal MDCs can persist and differentiate into myotubes and myofibers in the bladder wall.

METHODS

Primary MDCs isolated from normal mice were first transduced with adenovirus encoding the expression of the beta-galactosidase reporter gene. Adult severe combined immunodeficiency mice (n = 12) were used in this study. The MDCs were injected into the right and left lateral bladder walls with a 10-microL Hamilton microsyringe. The amount of injected MDCs ranged from 1 to 1.5 x 10(6) cells. The tissue was harvested after 5, 35, and 70 days, sectioned, stained for fast myosin heavy chain, and assayed for beta-galactosidase expression.

RESULTS

We observed a large number of cells expressing beta-galactosidase in the bladder wall at each time point. Many myotubes and myofibers expressing beta-galactosidase and positively stained for fast myosin heavy chain were also seen in the bladder wall at 35 and 70 days after injection. Additionally, the size of the injected MDCs significantly increased during the course of the study (P <0.05).

CONCLUSIONS

We have demonstrated the long-term survival and beta-galactosidase expression of MDCs injected into the bladder wall. Moreover, our results suggest that some injected MDCs can differentiate into myofibers. These results suggest that MDCs can be a desirable substance for tissue engineering and an ex vivo method for gene transfer into the lower urinary tract.

The role of receptors in the maturation-dependent adenoviral transduction of myofibers

One of the major hurdles facing the application of adenoviral gene transfer to skeletal muscle is the maturation-dependent transduction of muscle myofibers. It was recently proposed that the viral receptors (Coxsackie and adenovirus receptor (CAR) and the integrins alphavbeta3/beta5) play a major role in the poor adenoviral transduction of mature myofibers. Here we report the findings of morphological studies designed to determine experimentally the role of receptors in the adenoviral transduction of mature myofibers. First, we observed that the expression of both attachment and internalization receptors did not change significantly during muscle development. Second, when an extended tropism adenoviral vector (AdPK) that attaches to heparan sulfate proteoglycan (HSP) is used, a significant reduction of adenoviral transduction still occurs in mature myofibers despite HSP's high expression in mature skeletal muscle fibers. Third, when the adeno-associated virus (AAV) is used, which also utilizes HSP as a viral receptor, muscle fibers at different maturities can be highly transduced. Fourth, the pre-irradiation of the skeletal muscle of newborn mice to inactivate myoblasts dramatically decreased the transduction level of Ad and AdPK, but had no effect on AAV-mediated viral transduction of immature myofibers. These results taken together suggest that the viral receptor(s) is not a major determinant in maturation-dependent adenoviral transduction of myofibers.

Clonal isolation of muscle-derived cells capable of enhancing muscle regeneration and bone healing

Several recent studies suggest the isolation of stem cells in skeletal muscle, but the functional properties of these muscle-derived stem cells is still unclear. In the present study, we report the purification of muscle-derived stem cells from the mdx mouse, an animal model for Duchenne muscular dystrophy. We show that enrichment of desmin(+) cells using the preplate technique from mouse primary muscle cell culture also enriches a cell population expressing CD34 and Bcl-2. The CD34(+) cells and Bcl-2(+) cells were found to reside within the basal lamina, where satellite cells are normally found. Clonal isolation and characterization from this CD34(+)Bcl-2(+) enriched population yielded a putative muscle-derived stem cell, mc13, that is capable of differentiating into both myogenic and osteogenic lineage in vitro and in vivo. The mc13 cells are c-kit and CD45 negative and express: desmin, c-met and MNF, three markers expressed in early myogenic progenitors; Flk-1, a mouse homologue of KDR recently identified in humans as a key marker in hematopoietic cells with stem cell-like characteristics; and Sca-1, a marker for both skeletal muscle and hematopoietic stem cells. Intramuscular, and more importantly, intravenous injection of mc13 cells result in muscle regeneration and partial restoration of dystrophin in mdx mice. Transplantation of mc13 cells engineered to secrete osteogenic protein differentiate in osteogenic lineage and accelerate healing of a skull defect in SCID mice. Taken together, these results suggest the isolation of a population of muscle-derived stem cells capable of improving both muscle regeneration and bone healing.

The potential role of PDGF, IGF-1, TGF-beta expression in idiopathic pulmonary fibrosis

OBJECTIVE

To identify the role of cytokines involved in the development of lung fibrosis in patients with idiopathic-pulmonary fibrosis (IPF).

METHODS

Proteins and gene expression of platelet-derived growth factor (PDGF)-A and -B, insulin-like growth factor 1 (IGF-1), and transforming growth factor beta (TGF-beta) were measured in alveolar macrophages and open lung biopsies from patients with IPF using immunohistochemistry (IHC) and in situ hybridization (ISH).

RESULTS

In specimens of bronchoalveolar lavage fluid (BALF), PDGF-A, PDGF-B, IGF-1, TGF-beta were localized in alveolar macrophages. Evaluation of open lung biopsies from patients with IPF showed that IGF-1 was prominently present in pulmonary vessel walls in fibrotic lesions. PDGF and TGF-beta proteins were localized to hyperplastic bronchio-alveolar epithelial cells, alveolar macrophages, fibroblasts, vascular smooth muscle and endothelial cells. Our in situ hybridization results were consistent with that of immunohistochemistry except that PDGF-A and TGF-beta mRNA transcripts were not detected in bronchoalveolar epithelial cells.

CONCLUSION

These observations suggest that (1) alveolar macrophages play key roles not only in inflammation but also in the fibrotic process by releasing PDGF, IGF-1 and TGF-beta; (2) IGF-1 could be responsible for angiogenesis in IPF; (3) PDGF, TGF-beta are associated with fibroplasia and the deposition of extracellular matrix, as well as vessel remodeling and epithelial cell repopularization.

[Conformity of cancerous diagnosis of serum-fluorimetry under the influence of carotenoid fluorescence]

We observed that carotenoid had sensitization for fluorescence of porphyrin as cancerous diagnostic technology was applied in clinic by serum-fluorimetry. The Forster theory was used in order to analyse sensitized fluorescence between carotenoid and porphyrin in this paper. Transfer characteristic between energy donor and energy acceptor was calculated and discussed its influence on cancerous diagnosis.

[Advances in diagnosis and treatment of ectopic pregnancy during the past ten years]

OBJECTIVE

To investigate the changes of diagnosis and treatment of ectopic pregnancy (EP) during the past ten years.

METHODS

Medical records of 1,970 cases with EP seen in our hospital from Jan. 1987 to Dec. 1996 were collected and analyzed retrospectively.

RESULTS

(1) The incidence of EP increases from 1.0 per 42.4 labours during 1987-1988 to 1.0 per 6.6 labours in 1995-1996. (2) Diagnosis was confirmed more by television laparoscopy, transvaginal ultrasonography and sensitive human chorionic gonadotropin-beta subunit assay rather than loparotomy and with a shorter period, (6.5 +/- 0.7) days in 1987-1988 versus (3.7 +/- 0.2) days in 1995-1996. (3) The choice of treatment was more conservative or through laparoscopic surgery than abdominal salpingectomy. (4) The success rate of conservative surgery expectant management reached 100.0% and medical treatment with a variety of choices around 80.0%-85.%.

CONCLUSIONS

Although the incidence of EP increased, with the improvement of diagnostic approaches, patients were detected at an earlier stage and possible to be treated more conservatively.

The use of adeno-associated virus to circumvent the maturation-dependent viral transduction of muscle fibers

Muscle-based gene therapy using adenovirus, retrovirus, and herpes simplex virus has been hindered by viral cytotoxicity, host immune response, and the maturation-dependent viral transduction of muscle fibers. The development of new mutant vectors has greatly reduced the toxicity and the immune rejection problems, but the inability of viral vectors to penetrate and transduce mature myofibers remains an important issue. Research has been focused on the characterization of barriers to viral transduction in mature myofibers to develop strategies to circumvent the maturation-dependent viral transduction of myofibers. Here, we report that adeno-associated virus (AAV) can be used to overcome the maturation-dependent viral transduction of myofibers. We have investigated by which mechanism AAV can penetrate and efficiently transduce mature muscle fibers, and have shown that this viral vector is not blocked by the basal lamina and that AAV transduction of myofibers is independent of myoblast mediation. Although AAV can efficiently transduce mature myofibers, a differential transduction is still observed among the different types of myofibers that correlates with the expression of the heparan sulfate proteoglycan receptors, the muscle maturity, the number of viral particles used, and the time postinjection. The identification of the mechanisms by which AAV transduces mature myofibers will help in the development of strategies to achieve an efficient muscle-based gene therapy for inherited and acquired diseases.

Spontaneous improvement in reduced vasodilatory capacity in major cerebral arterial occlusive disease

Reduced vasodilatory capacity resulting from occlusive lesions of the major cerebral arteries may return to normal without surgical revascularisation. We aimed to determine prospectively the frequency and predictors of recovery of impaired haemodynamics as demonstrated by acetazolamide (ACZ) reactivity on single-photon emission computed tomography (SPECT). Vasoreactivity was measured by (123)I-IMP SPECT with an ACZ challenge, in 37 medically treated patients with unilateral occlusive disease of the internal carotid or middle cerebral artery at an interval of 1-2 years. Each ACZ challenge test was analysed semiquantitatively by calculating the degree of increase in cerebral blood flow (CBF) asymmetry after ACZ administration (DeltaAI). Vasodilatory capacity was abnormal initially in 20 patients (65 %); eight of whom (40 %) exhibited spontaneous normalisation on follow-up. Although the baseline characteristics did not differ significantly between patients with or without increase in reactivity, logistic regression analysis revealed that the initial DeltaAI (P < 0.05) and the type of vascular lesion (stenosis or occlusion) (P < 0.05) correlated significantly with a return towards normal of reduced ACZ reactivity. Spontaneous improvement of impaired vasodilatory capacity may not be a rare phenomenon. We found that mild reduction in the initial ACZ reactivity and a stenosis, but not complete occlusion, were independent factors contributing to normalisation of impaired cerebral haemodynamics.

[The potential role of cytokine expression and its relation to angiogenesis in idiopathic pulmonary fibrosis]

OBJECTIVE

The expression of insulin-like growth factor (IGF)-I and platelet-derived growth factor (PDGF) in open lung biopsies from patients with idiopathic pulmonary fibrosis (IPF) was studied to investigate their precise role in the development of fibrosis in IPF.

METHODS

The distribution and expression of IGF-I and PDGF were examined in lung sections of IPF patients with antibodies and cDNA probes of IGF-I and PDGF by immunohistochemistry and in situ hybridization.

RESULTS

IGF-I was predominantly localized in vascular smooth muscle cells and vascular endothelial cells of newly formed vessels in IPF. Smooth muscle cells of pulmonary arteries which underwent hypertrophy and hyperplasia strongly expressed IGF-I (+ + +). Type II cells, alveolar macrophages, and interstitial cells were also stained with anti-IGF-I, but with lesser intensity (+). PDGF-AA and BB were localized in hyperplastic bronchio-alveolar epithelial cells and interstitial fibroblasts (+ + +). Alveolar macrophages, vascular endothelial cells and smooth muscle cells were also stained positive (+ +).

CONCLUSION

IGF-I and PDGF promote angiogenesis and vascular smooth muscle cell hypertrophy and hyperplasia, which contribute to the progression of fibrosis in IPF. IGF-I and PDGF are also involved in reepithelization and fibroproliferation in IPF through interaction with mesenchymal cells.

Extended tropism of an adenoviral vector does not circumvent the maturation-dependent transducibility of mouse skeletal muscle

BACKGROUND

Efficient adenoviral gene delivery to mature skeletal muscle has been hindered by different factors. The low levels of adenoviral attachment receptor (CAR) that have been reported in this tissue may be a limiting factor. Therefore, adenoviral transduction of mature muscle may be improved by extending the tropism of the adenoviral vectors to attachment receptors that are highly expressed in mature myofibers. In this study, we have investigated whether an extended tropism adenoviral vector which additionally attaches to the broadly expressed heparan-containing receptors (AdPK) can bypass the maturation-dependent adenoviral transducibility of mouse skeletal muscle.

METHODS

The adenoviral vector AdPK carrying the LacZ gene was evaluated as a gene delivery vehicle in mouse skeletal muscle at different maturities in vitro and in vivo. The viral transduction efficiencies were determined by histochemical and ONPG analysis of the beta-galactosidase activity level.

RESULTS

Higher transduction efficiencies were detected in immature muscle from normal mice, and in mature muscle from merosin-deficient dy/dy mice (carrying myofibers with an impaired extracellular matrix) and dystrophin-deficient mdx mice (showing a high level of myoblast activity) when compared to mature muscle from normal mice.

CONCLUSION

Despite the enhanced attachment characteristics, the extended tropism adenoviral vector is, similarly to the wild-type adenoviral vector in previous studies, still hindered by both a protective extracellular matrix and the diminished myoblast-mediation in mature muscle.

Loss of heterozygosity, by mitotic gene conversion and crossing over, causes strain-specific adenine mutants in constitutive diploid Candida albicans

Molecular evidence is provided in this paper to elucidate a long-standing intriguing phenomenon in fungal genetics: that many natural isolates of the constitutive diploid organism Candida albicans yield strain-specific, recessive mutants at a reproducible frequency that is as high as a few percent of the surviving cells after exposure to UV irradiation or other mutagens. Southern hybridization analysis and DNA sequence data indicated that C. albicans CA12, a clinical isolate, is heterozygous for the ADE2 gene, carrying one functional and one null allele. Sequence analysis of the null allele revealed the presence of a 1.3 kb deletion, which locates between two AATC repeats and spans the promoter and coding regions of the gene. The adenine auxotrophic mutants, which were readily isolated after UV irradiation of C. albicans CA12, were proved to be the segregants of mitotic recombination as they remained as diploid, not hemizygous or haploid, cells and were homozygous for ade2. Analysis of reciprocal products of the mitotic recombination detected that the process of loss of heterozygosity was mediated by mitotic crossing over (reciprocal exchange of genetic information) as well as gene conversion (non-reciprocal exchange of genetic information).

Secondary structure peptide mimetics: design, synthesis, and evaluation of beta-strand mimetic thrombin inhibitors

Constrained dipeptide mimetic templates were designed to mimic the secondary structure of peptides in a beta-strand conformation. Two templates corresponding to the D-Phe-Pro portion of the thrombin inhibitor D-Phe-Pro-ArgCH2Cl were synthesized and converted into nine alpha-ketoamide and alpha-ketoheterocycle inhibitors of thrombin. Additionally, a template corresponding to L-Phe-Pro was synthesized and converted to a thrombin inhibitor. The in vitro inhibition of thrombin by these compounds was determined, and those corresponding to the D-Phe-Pro were found to be more potent inhibitors than the L-Phe-Pro mimetic. The alpha-ketoamides were found to be more potent than the alpha-ketoheterocycles but had much slower on rates. By comparison of a series of alpha-ketoamide analogues, it is apparent that the there is a preference for binding of bulky hydrophobic substituents in the P' portion of the thrombin active site. Three of the inhibitors (MOL098, MOL144, and MOL174) were screened against a series of coagulation and anticoagulation enzymes and found to be selective for inhibition of the coagulation enzymes. Two of the inhibitors were tested in in vitro models of intestinal absorption and found to have low absorption potential. The compounds were then tested in vivo in both rats and primates, and one of them (MOL144) was approximately 25% absorbed in both species. This study has delineated the synthesis of constrained dipeptide beta-strand mimetics and validated the potential for compounds of this type as potent thrombin inhibitors and possible drug leads.

[The effect of age on the regional blood flow of neck of femur in normal Chinese]

This study aimed to assess the effect of age on the regional blood flow of neck of femur in normal Chinese. 133Xe washout method was adopted. The result showed that the femur regional blood flow of normal Chinese decreased slowly with the increase of their age. The relation between age and femur blood flow might be expressed as F = -0.042Y + 9.01(F refers to blood flow, Y refers to age). The average femur regional blood flow of normal Chinese was 7.37 +/- 0.62 ml.(100 g.min)-1 for 21-40 years old. The authors suggest this result can be considered to stand for regional femur blood flow of young healthy adults.

[The potential role of cytokines expression in idiopathic pulmonary fibrosis]

OBJECTIVE

To investigate the protein and gene expression in bronchoalveolar lavage cells and open lung biopsies from patients with IPF.

METHODS

The immunohistochemical methods were used to analyze the expression of PDGF, TGF-beta in bronchoalveolar lavage cells of patients with IPF. For open lung biopsies, both immunohistochemistry and in situ hybridization were used.

RESULTS

In specimens of bronchoalveolar lavage fluid, PDGF-AA, PDGF-BB, TGF-beta were localized to alveolar macrophages in patients with IPF. Though there were no differences between IPF and sarcoidosis in terms of the staining intensity (2.5 - 3.0) or number of positive cells 81% - 90%, the number of such cells were less in the control (0 - 1.7, 25% - 32% respectively). Evaluation of open lung biopsies from patients with IPF showed that PDGF, TGF-beta proteins were localized to hyperplastic bronchio-alveolar epithelial cells (2.4 - 3.7, in control 0), alveolar macrophages (2.9 - 3.7, in control 0.8 - 1.3), fibroblasts (3.0 - 3.6, in control 2.7 - 2.8), vascular smooth muscle cells, vascular endothelial cells, and fibroblast-like cells surrounding pulmonary vessels (2.7 - 4.0, in control 2.1 - 2.9). In situ hybridization results were consistent with that of immunohistochemistry except that PDGF and TGF-beta mRNA transcripts were not detected in bronchio-alveolar epithelial cells. In control lungs, however, both ISH and IHC revealed that PDGF and TGF-beta were only present in the pleura and in fibroblast-like cells surrounding pulmonary vessels.

CONCLUSIONS

PDGF and TGF-beta, which interplay with pulmonary mesenchymal cells, are involved in fibroplasia and deposition of extracellular matrix as well as angiogenesis and epithelial cell repopularization.

[Clinical significance of detection of IL-2R for non-small cell lung cancer.]

BACKGROUND

To explore the clinical significance of SIL-2R of serum and IL-2R expression of cancer tissue in non-small cell lung cancer.

METHODS

SIL-2R levels in the serum and IL-2R expression in cancer tissues were detected in 42 non-small cell lung cancer by ELISA and immunohistochemistry respectively.

RESULTS

Serum SIL-2R level was significantly higher in lung cancer group than that in normal control group ( P < 0. 05) , and significantly higher in stage III, IV disease than that in stage I, II disease ( P < 0. 05) , but it was not associated with histological classification of the cancer ( P > 0. 05) . IL-2R expression was significantly higher in lung cancer tissue than that in normal lung tissue ( P < 0. 05) and was significantly higher in stage III, IV cancer than that in stage I, II cancer ( P < 0. 05) . But it was not related to cancer types ( P > 0. 05) .

CONCLUSIONS

The results suggest that detection of serum SIL-2R and IL-2R expression of the cancer tissue might be useful to predict stages of cancer and monitor the prognosis of patients with lung cancer.

Highly efficient and versatile synthesis of libraries of constrained beta-strand mimetics

The general approach of using a bicyclic template to produce inhibitors of the protease superfamily of enzymes has been investigated. The Diels Alder cycloaddition reaction on solid support has been found to be highly efficient for the synthesis of libraries of compounds that mimic the beta-strand secondary structure of proteins. Several potent and selective inhibitors of proteases have been discovered.

[Alteration in regional blood flow in minipigs' femur under inadequate decompression studied by isotopes washout method]

We studied the alteration in regional blood flow in minipigs' femur under inadequate decompression after hyperbaric air exposure. The animals were placed in the hyperbaric chamber and exposed to the pressure of 0.5 MPa for 1.5 h, which was reduced to atmosphere at an ascent rate of 0.03-0.04 MPa/min. Regional blood flow in the femur was measured by the isotopes washout method of inhaling 133Xe. The radioactivity was monitored by a multifunctional blood flowmeter interfaced to a minicomputer. Before exposure, the values of average blood flow (F) of femur on the left and right were 15.4 +/- 1.8 and 16.9 +/- 2.0 ml/100 g.min respectively. The values of blood flow (f1) of hematopoietic marrow were 19.1 +/- 2.0 and 21.3 +/- 2.0 ml/100 g.min (n = 7). After inadequate decompression, F values were reduced to 10.3 +/- 1.8 and 11.1 +/- 1.6 ml/100 g.min and f1 values reduced to 13.9 +/- 1.4 and 13.8 +/- 1.0 ml/100 g.min (n = 7), which were obviously lower than those before exposure (P < 0.05). This experiment showed that significant reduction in blood flow in the femur region occurred under inadequate decompression after the exposure of minipigs hyperbaric environment, suggesting that ischemia is a causative factor of osteonecrosis.

Adenine auxotrophic heterozygosity in Candida krusei

Candida krusei CK 18 carries heterozygosity for a recessive adenine biosynthesis allele, as it can be induced by UV irradiation to form adenine mutants at high frequency. The resultant mutants were characterized with the phenotype of red colony and residual growth on minimal media. The majority of the descendant prototrophic segregates were capable of continuous segregation to adenine mutants, suggesting gene conversion as one possible mechanism for the occurrence of the adenine auxotroph in the isolate.