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31.
Multiplicity of peptide permeases in Candida albicans: evidence from novel chromophoric peptides. 总被引:3,自引:1,他引:2 下载免费PDF全文
Evidence is presented for the presence of multiple peptide permeases in the eucaryotic organism Candida albicans. Instrumental in these studies were the peptides L-alanyl-L-2-thiophenylglycine (Ala-alpha-TPG) and L-alanyl-L-2-thiophenylglycyl-L-alanine (Ala-alpha-TPG-Ala), which contain thiophenol attached to the alpha-carbon of glycine. Subsequent to transport into the fungal cell, enzymatic hydrolysis of these peptides resulted in the release of free thiophenol, which was quantified by using Ellman reagent. Thiophenol release was shown to be directly correlated to peptide transport and hydrolysis, with transport being the rate-limiting step in intact cells. These peptides, whose uptake showed Michaelis-Menten kinetics, have been used to determine peptide uptake in C. albicans. In addition, we found that the intracellular peptidases can readily be assayed in permeabilized cells and that bestatin, an aminopeptidase inhibitor, inhibits all detectable peptidase activity. C. albicans 124 was able to transport and hydrolyze both Ala-alpha-TPG and Ala-alpha-TPG-Ala, whereas the mutant (124NIK5) was able to transport only the tripeptide. The intracellular peptidases of this mutant were unaffected. In wild-type C. albicans 124, oligopeptides were able to compete with uptake of Ala-alpha-TPG-Ala to a far greater extent than with that of Ala-alpha-TPG; dipeptides inhibited uptake of both Ala-alpha-TPG and Ala-alpha-TPG-Ala. These results provide complementary evidence for the existence of distinct transport systems. 相似文献
32.
Primary cultures of bovine adrenocortical cells (BAC) were used to determine whether the adrenal microsomal 3 beta-hydroxysteroid dehydrogenase-isomerase complex (3 beta-HSD), like the 17 alpha-hydroxylase (17-OHase), responded to ACTH treatment with an increase in activity. Both enzymes influence the steroidogenic path leading to 17 alpha-hydroxyprogesterone formation and thus could affect adrenal androgen biosynthesis. 3 beta-HSD Activity in postmitochondrial supernatant fluid, homogenates or cell monolayers remained unchanged after cells had been maintained in 1 microM ACTH up to 48 h. Since ACTH exposure led to a marked increase in 17-OHase activity over the same time period, it is concluded that, under the conditions used, the 3 beta-HSD-isomerase complex in BAC is nonresponsive to tropic hormone treatment. 相似文献
33.
Seymour S. Cohen Ram K. Sindhu Michael Greenberg Bauri Yamanoha Robert Balint Kevin McCarthy 《Plant Growth Regulation》1985,3(3-4):227-238
Leaves of Chinese cabbage from healthy plants or from those infected with turnip yellow mosaic virus yield protoplasts which convert methionine to protein, S-adenosylmethionine, decarboxylated S-adenosylmethionine, spermidine, spermine and 1-aminocyclopropane-1-carboxylate. The enzyme spermidine synthase is entirely cytosolic and has been purified extensively. An inhibitor of this enzyme, dicyclohexylamine, blocks spermidine synthesis in intact protoplasts, and in so doing stimulates spermine synthesis. Aminoethoxyvinylglycine blocks the conversion of S-adenosylmethionine to 1-aminocyclopropane-1-carboxylate, the precursor to ethylene, in protoplasts. This inhibitor markedly stimulates the synthesis of both spermidine and spermine. Essentially all the protoplasts obtained from new leaves of plants infected 7 days earlier are infected. On incubation, such protoplasts convert exogenous methionine to viral protein and viral spermidine whose specific radioactivity is twice that of total cell spermidine. Exogeneous spermidine is also converted to cell putrescine and viral spermidine and spermine. Normal and virus-infected cells are being studied for their content of phenolic acid amides of the polyamines. 相似文献
34.
C D Perchonock I Uzinskas T W Ku M E McCarthy W E Bondinell B W Volpe J G Gleason B M Weichman R M Muccitelli J F DeVan 《Prostaglandins》1985,29(1):75-81
A series of desamino-2-nor-leukotriene analogs has been prepared by the reaction of various thiols with several methyl trans-4,5-epoxy-6Z-alkenoates, followed by deprotection. The products were assessed for their ability to antagonize the LTD4-induced contraction of the isolated guinea pig trachea. Several compounds displayed potent leukotriene antagonist activity, i.e., KB values in the sub-micromolar range, while only minimally affecting basal airway tone. The most potent analog, 4-hydroxy-5-(2-carboxyethylthio)-6Z-nonadecenoic acid, antagonized both LTD4- and LTE4-induced contractions of the trachea in an apparently competitive fashion. These agents possess increased potency relative to SK&F 101132, the first leukotriene analog identified as having LT-antagonist activity. Thus, these results demonstrate that deletion of the peptide amino group can produce leukotriene analogs which have minimal intrinsic contractile activity on the isolated guinea pig trachea, yet possess potent leukotriene-antagonistic effects. 相似文献
35.
Review of the morbidity of 300 free-flap donor sites 总被引:1,自引:0,他引:1
Donor-site morbidity in 300 consecutive free flaps was reviewed to identify their etiologies and potentially prevent their recurrence in future cases. An overall morbidity rate of 20 percent was seen in this series. Secondary surgical procedures specific for donor-site problems were required in 7.7 percent of patients. Major complications occurred in 2.3 percent of the donor sites. From this review it is apparent that major donor-site morbidity is uncommon and most donor-site problems could probably have been avoided. Our recommendations are as follows: closure of the donor site to avoid excessive tension must be carefully planned preoperatively, donor-site anatomy and flap elevation techniques must be precisely understood, surgical retractors must be carefully placed to avoid injury to nearby structures, the donor site should be closed immediately following pedicle division, thus minimizing wound exposures, and complete surgical hemostasis is mandatory. 相似文献
36.
Enhancement of translational efficiency by the Escherichia coli atpE translational initiation region: its fusion with two human genes 总被引:10,自引:0,他引:10
The cDNA sequences encoding mature human interleukin 2 (IL2) and beta-interferon (INF beta), respectively, were fused with various translational initiation regions and inserted into two different types of expression vector. The relative levels of expression of the two genes and the functional stability of their respective mRNAs were examined in vivo in Escherichia coli hosts. The addition of the 30-bp sequence, found immediately upstream of the E. coli atpE gene Shine-Dalgarno (SD) sequence, to the translational initiation regions of IL2 and INF beta increased the expression of both these genes by a factor of 6-10. Thus this sequence, which naturally acts within the E. coli atp operon to enhance the translational initiation frequency of the atpE gene, can increase the expression of other genes in E. coli. It may exemplify a specific type of recognition signal for the E. coli translational apparatus. 相似文献
37.
Assignment of orthologous relationships among mammalian alpha-globin genes by examining flanking regions reveals a rapid rate of evolution 总被引:1,自引:0,他引:1
In order to study the relationships among mammalian alpha-globin genes, we
have determined the sequence of the 3' flanking region of the human alpha 1
globin gene and have made pairwise comparisons between sequenced
alpha-globin genes. The flanking regions were examined in detail because
sequence matches in these regions could be interpreted with the least
complication from the gene duplications and conversions that have occurred
frequently in mammalian alpha-like globin gene clusters. We found good
matches between the flanking regions of human alpha 1 and rabbit alpha 1,
human psi alpha 1 and goat I alpha, human alpha 2 and goat II alpha, and
horse alpha 1 and goat II alpha. These matches were used to align the
alpha-globin genes in gene clusters from different mammals. This alignment
shows that genes at equivalent positions in the gene clusters of different
mammals can be functional or nonfunctional, depending on whether they
corrected against a functional alpha-globin gene in recent evolutionary
history. The number of alpha-globin genes (including pseudogenes) appears
to differ among species, although highly divergent pseudogenes may not have
been detected in all species examined. Although matching sequences could be
found in interspecies comparisons of the flanking regions of alpha- globin
genes, these matches are not as extensive as those found in the flanking
regions of mammalian beta-like globin genes. This observation suggests that
the noncoding sequences in the mammalian alpha-globin gene clusters are
evolving at a faster rate than those in the beta-like globin gene clusters.
The proposed faster rate of evolution fits with the poor conservation of
the genetic linkage map around alpha-globin gene clusters when compared to
that of the beta-like globin gene clusters. Analysis of the 3' flanking
regions of alpha-globin genes has revealed a conserved sequence
approximately 100-150 bp 3' to the polyadenylation site; this sequence may
be involved in the expression or regulation of alpha-globin genes.
相似文献
38.
A glycoprotein associated with malignancy was purified from the 0.6M perchloric acid-soluble fraction of serum obtained from cancer patients. The purified glycoprotein contained sialic acid, which was responsible for binding to wheat-germ agglutinin-Sepharose. Gel electrophoresis showed one band with an apparent Mr of 50 000-55 000, and the isoelectric point was 4.4 +/- 0.1. The glycoprotein could be distinguished from carcinoembryonic antigen and alpha-fetoprotein. Iodination of this material with chloramine-T permitted development of a radioimmunoassay. 相似文献
39.
40.
Twelve singly embedded isolates (SEV) and two multiply embedded isolates (MEV) of nuclear polyhedrosis viruses from Heliothis larvae were compared by time-mortality assays in neonate H. zea larvae. The isolates could be separated into six groups based on differences in the 50% survival time (ST50) values. Isolates with identical restriction endonuclease (REN) profiles did not differ significantly in their ST50 values, whereas isolates with several different REN cleavage sites also had significantly different ST50 values. With the exception of one isolate from India, the singly embedded isolates acted faster than the multiply embedded isolates. 相似文献