摘要:

AbstractSeveral mutant forms of Staphylococcal nuclease with one or two defined amino acid substitutions have been purified, and the effects of the altered amino acid sequence on the stability of the folded conformation have been analyzed by guanidine hydrochloride denaturation. Twonuc‐ mutations, which greatly reduced the level of enzyme activity accumulated inEcolicolonies carrying a recombinant plasmid with the mutantnucgene (i.e., a NUC‐phenotype), both result in protein unfolding at significantly lower guanidine hydrochloride concentrations than the wild‐type protein, whereas threesupmutations isolated on the basis of their ability to suppress partially the NUC‐phenotype of the above two mutations result in unfolding at significantly higher guanidine hydrochloride concentrations. Characterization of nuclease molecules with two different amino acid substitutions, eithernuc−+suppairs orsup+suppairs, suggests that the effect of an amino acid substitution on the stability of the native conformation, as measured by the value of ΔΔGD, may not be a constant, but rather a variable that is sensitive to the presence of other substitutions at distant sites in the same molecule. Surprisingly, the slopes of the log Kappvs guanidine hydrochloride concentration plots vary by as much as 35% among the differe

ISSN:0730-2312    

DOI:10.1002/jcb.240300402

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1986

数据来源: WILEY

摘要:

AbstractThe traditional approach of using homologous sequences to elucidate the role of specific amino acid residues in protein structure and function becomes more meaningful as the number of differences is minimized, with the limit being alteration of a single residue. For small proteins in solution, NMR spectroscopy offers a means of obtaining detailed information about each residue and its response to a given change in the protein sequence. Extraction of this information has been aided by recent progress in spectrometer technology (higher magnetic fields, more sensitive signal detection, more sophisticated computers) and experimental strategies (new NMR pulse sequences including multiple‐quantum and two‐dimensional NMR methods). The set of avian ovomucoid third domains, which consists of the third domain proper plus a short leader (connecting peptide) and has a maximum of 56 amino acid residues, offers an attractive system for developing experimental methods for investigating sequence‐structure and structure‐function relationships in proteins. Our NMR results provide examples of sequence effects on pKa′ values, average conformation, and internal motion of amino acid si

ISSN:0730-2312    

DOI:10.1002/jcb.240300403

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1986

数据来源: WILEY

摘要:

AbstractThe in vitro growth of primary erythroleukemia cells has been examined in the presence and absence of the hormone erythropoietin (EPO). Although these leukemic cells had previously been considered to be hormone‐independent, addition of EPO was found to be essential for maximum growth in culture. Erythroid colonies that grew in the presence of EPO were leukemogenic when returned to mice. Influence of EPO on the in vivo growth of leukemic cells was indicated by our findings that (1) administration of the hormone caused a more severe leukemia and rapid death, and (2) transfusion of red blood cells, which lowers endogenous EPO, led to decreased spleen size and increased survival of leukemic mice. We suggest from our results that hormone‐associated therapy might be efficacious in the treatment of this and, perhaps, other leukem

ISSN:0730-2312    

DOI:10.1002/jcb.240300404

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1986

数据来源: WILEY

摘要:

AbstractThe polymorphic restriction fragments of the human Ha‐raslocus, produced by the variable tandem repetition (VTR) of a short consensus sequence, fall into three classes based on allelic frequencies. Alleles of the “rare” class (individual frequencies<0.5%) have been detected only in white blood cell and tumor DNA of cancer patients. This phenomenon is independent of ethnic origin. No significant association of rare alleles with cancer patients has been demonstrated at an independent tandem repeat locus, VTR4.1. The results suggest that the Ha‐rasrestriction fragment length polymorphism is useful in cancer risk ass

ISSN:0730-2312    

DOI:10.1002/jcb.240300405

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1986

数据来源: WILEY

摘要:

AbstractProperties of catalase activities have been examined in the intact cells of early stationary phase and cells 3 hr after transfer to sporulation medium inSaccharomyces cerevisiae. The catalase activities of the two cells had a broad optimal pH from 6 to 8. Catalase activity in the intact cells increased throughout a 4‐hr period of the observation following transfer to sporulation medium. Almost all the catalase activity in vegetative cells was lost by the treatment at 60°C for 10 min. Catalase activities of both cells were inhibited by KCN, NaN3, o‐phenanthroline, and PCMB. The catalase activity of the vegetative cells was slightly more inhibited and inactivated than that of the sporulating cells by the inhibitors and by the treatment with HCl or

ISSN:0730-2312    

DOI:10.1002/jcb.240300406

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1986

数据来源: WILEY

摘要:

AbstractAn amphibian egg recovered from the body cavity is enclosed by a coelomic egg envelope. Upon transport down the oviduct, the envelope is converted to the vitelline envelope. The coelomic and vitelline envelopes are distinct in terms of sperm penetrability, ultrastructural morphology, and radioiodination profiles. In this study, the macromolecular compositions of these two envelopes were determined. Isolated envelopes were compared by one‐ and two‐dimensional gel electrophoresis, peptide mapping, and radiolabeling. A protein with a molecular weight of 57,000 (57K) was present in the vitelline envelope but was absent in the coelomic envelope. A glycoprotein with a molecular weight of 43K in the coelomic envelope was converted to a component with a molecular weight of 4lK in the vitelline envelope. The 43K‐molecular weight component of the coelomic envelopes could be radioiodinated by lactoperoxidase but no labeling of the 41K‐molecular weight component occurred in the vitelline envelope. Peptide mapping using limited proteolysis established that the 43K‐molecular weight component of the coelomic envelope was a precursor to the 41K‐molecular weight component of the vitelline envelope. These molecular alterations may underlie the ultrastructural and physiological changes occurring in thes

ISSN:0730-2312    

DOI:10.1002/jcb.240300407

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1986

数据来源: WILEY

摘要:

AbstractWe have developed a simple and rapid method for isolation of purified nuclear lamina from Ehrlich ascites tumor cells. The procedure employs chromatin structures prepared from whole cells at low ionic strength and is carried out under conditions that minimize the formation of artifactual protein‐DNA complexes. When the isolation is performed in the presence of EDTA, nuclear lamina without distinct pore complexes is obtained. In the absence of EDTA, intact pore complexes and a large amount of vimentin 100 A filaments are seen associated with nuclear lamina. The main nuclear lamina proteins are characterized using gel electrophoresis, immunoblotting, and two‐dimensional peptide mapping. An extensive structural homology is found between lamin A and lamin C. whose peptide maps differ by only one major spot, whereas lamin B has apparently unrelated patt

ISSN:0730-2312    

DOI:10.1002/jcb.240300408

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1986

数据来源: WILEY

摘要:

AbstractProteins involved in a structural transition detected in red blood cell membranes at 40°C by spin labeling methods have been investigated. Antibodies specific for spectrin, band 3, and protein 4.1 have been used as specific probes to modify membrane thermotropic properties. Spectrin seems to be involved in a 40°C transition detected in ghosts by both a stearic acid spin label (16‐doxyl stearic) and a sulfhydryl‐specific maleimide analogue spin label. Circular dichroism and maleimide spin labeling studies of purified spectrin show a slow unfolding of the protein structure starting at 25‐30°C and a massive transition with an onset temperature of 48 and 40°C, respectively. This thermotropic behavior of spectrin could be the process that modifies membrane physicochemical properties above 40°C that are detected by the stearic acid spin label. The transition detected by the stearic acid spin label was modified both by antispectrin antibodies and anti‐4.1 protein antibodies, but not by antibodies specific for the cytoplasmic domain of band 3. These results suggest an involvement of protein 4.1 in regulating spectrin unfolding at the membrane level. A selective inhibition of the transition detected by the maleimide spin label has been obtained with a monoclonal antispectrin antibody at 1 : 1 molar ratio. The involvement in this transition of a localised spectrin domain(s) containing few exposed sulfhydryl groups

ISSN:0730-2312    

DOI:10.1002/jcb.240300409

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1986

数据来源: WILEY

ISSN:0730-2312    

DOI:10.1002/jcb.240300401

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1986

数据来源: WILEY