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sentences

{"project":"sentences","denotations":[{"id":"T1","span":{"begin":0,"end":81},"obj":"Sentence"},{"id":"T2","span":{"begin":82,"end":142},"obj":"Sentence"},{"id":"T3","span":{"begin":143,"end":401},"obj":"Sentence"},{"id":"T4","span":{"begin":402,"end":590},"obj":"Sentence"},{"id":"T5","span":{"begin":591,"end":707},"obj":"Sentence"},{"id":"T6","span":{"begin":708,"end":841},"obj":"Sentence"},{"id":"T7","span":{"begin":842,"end":985},"obj":"Sentence"},{"id":"T8","span":{"begin":986,"end":1214},"obj":"Sentence"},{"id":"T9","span":{"begin":1215,"end":1339},"obj":"Sentence"},{"id":"T10","span":{"begin":1340,"end":1502},"obj":"Sentence"},{"id":"T11","span":{"begin":1503,"end":1625},"obj":"Sentence"},{"id":"T12","span":{"begin":1626,"end":1747},"obj":"Sentence"},{"id":"T13","span":{"begin":1748,"end":1866},"obj":"Sentence"},{"id":"T14","span":{"begin":1867,"end":2094},"obj":"Sentence"},{"id":"T15","span":{"begin":2095,"end":2241},"obj":"Sentence"}],"namespaces":[{"prefix":"_base","uri":"http://pubannotation.org/ontology/tao.owl#"}],"text":"A K319N/E325Q double mutant of the lactose permease cotransports H+ with lactose. Implications for a proposed mechanism of H+/lactose symport.\nIn this study, we have examined the transport characteristics of the wild-type lactose permease, single mutants in which Lys-319 was changed to asparagine or alanine or Glu-325 was changed to glutamine or alanine, and the corresponding double mutant strains. The wild-type and Asn-319 mutant showed high levels of lactose uptake, with Km values of 0.42 and 1.30 mM and Vmax values of 102.6 and 48.3 nmol of lactose/min/mg of protein, respectively. The Asn-319/Gln-325 strain had a normal Km of 0.36 mM and a moderate Vmax of 18.5 nmol of lactose/min/mg of protein. By comparison, the single E325Q strain had a normal Km of 0.27 mM but a very defective Vmax of 1.3 nmol of lactose/min/mg of protein. A similar trend was observed among the alanine substitutions at these positions, although the Vmax values were lower for the Ala-319 mutations. When comparing the Vmax values between the single position 325 mutants with those of the double mutants, these results indicate that neutral 319 mutations substantially alleviate a defect in Vmax caused by neutral 325 mutations. With regard to H+/lactose coupling, the wild-type permease is normally coupled and can transport lactose against a gradient. The position 325 single mutants showed no evidence of H+ transport with lactose or thiodigalactoside (TDG) and were unable to facilitate uphill lactose transport. The single Asn-319 mutant and double Asn-319/Gln-325 mutant were able to transport H+ upon the addition of lactose or TDG. In addition, both of these strains catalyzed a sugar-dependent H+ leak that inhibited cell growth in the presence of TDG. These two strains were also defective in uphill transport, which may be related to their sugar-dependent leak pathway. Based on these and other results in the literature, a model is presented that describes how the interactions among several ionizable residues within the lactose permease act in a concerted manner to control H+/lactose coupling. In this model, Lys-319 and Glu-325 play a central role in governing the ability of the lactose permease to couple the transport of H+ and lactose."}

GlyCosmos15-Glycan

GlyCosmos15-Sentences

{"project":"GlyCosmos15-Sentences","blocks":[{"id":"T1","span":{"begin":0,"end":81},"obj":"Sentence"},{"id":"T2","span":{"begin":82,"end":142},"obj":"Sentence"},{"id":"T3","span":{"begin":143,"end":401},"obj":"Sentence"},{"id":"T4","span":{"begin":402,"end":590},"obj":"Sentence"},{"id":"T5","span":{"begin":591,"end":707},"obj":"Sentence"},{"id":"T6","span":{"begin":708,"end":841},"obj":"Sentence"},{"id":"T7","span":{"begin":842,"end":985},"obj":"Sentence"},{"id":"T8","span":{"begin":986,"end":1214},"obj":"Sentence"},{"id":"T9","span":{"begin":1215,"end":1339},"obj":"Sentence"},{"id":"T10","span":{"begin":1340,"end":1502},"obj":"Sentence"},{"id":"T11","span":{"begin":1503,"end":1625},"obj":"Sentence"},{"id":"T12","span":{"begin":1626,"end":1747},"obj":"Sentence"},{"id":"T13","span":{"begin":1748,"end":1866},"obj":"Sentence"},{"id":"T14","span":{"begin":1867,"end":2094},"obj":"Sentence"},{"id":"T15","span":{"begin":2095,"end":2241},"obj":"Sentence"}],"text":"A K319N/E325Q double mutant of the lactose permease cotransports H+ with lactose. Implications for a proposed mechanism of H+/lactose symport.\nIn this study, we have examined the transport characteristics of the wild-type lactose permease, single mutants in which Lys-319 was changed to asparagine or alanine or Glu-325 was changed to glutamine or alanine, and the corresponding double mutant strains. The wild-type and Asn-319 mutant showed high levels of lactose uptake, with Km values of 0.42 and 1.30 mM and Vmax values of 102.6 and 48.3 nmol of lactose/min/mg of protein, respectively. The Asn-319/Gln-325 strain had a normal Km of 0.36 mM and a moderate Vmax of 18.5 nmol of lactose/min/mg of protein. By comparison, the single E325Q strain had a normal Km of 0.27 mM but a very defective Vmax of 1.3 nmol of lactose/min/mg of protein. A similar trend was observed among the alanine substitutions at these positions, although the Vmax values were lower for the Ala-319 mutations. When comparing the Vmax values between the single position 325 mutants with those of the double mutants, these results indicate that neutral 319 mutations substantially alleviate a defect in Vmax caused by neutral 325 mutations. With regard to H+/lactose coupling, the wild-type permease is normally coupled and can transport lactose against a gradient. The position 325 single mutants showed no evidence of H+ transport with lactose or thiodigalactoside (TDG) and were unable to facilitate uphill lactose transport. The single Asn-319 mutant and double Asn-319/Gln-325 mutant were able to transport H+ upon the addition of lactose or TDG. In addition, both of these strains catalyzed a sugar-dependent H+ leak that inhibited cell growth in the presence of TDG. These two strains were also defective in uphill transport, which may be related to their sugar-dependent leak pathway. Based on these and other results in the literature, a model is presented that describes how the interactions among several ionizable residues within the lactose permease act in a concerted manner to control H+/lactose coupling. In this model, Lys-319 and Glu-325 play a central role in governing the ability of the lactose permease to couple the transport of H+ and lactose."}

Glycan-GlyCosmos

PubMed:9933600 JSONTXT

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sentences

GlyCosmos15-Glycan

GlyCosmos15-Sentences

Glycan-GlyCosmos

PubMed:9933600 JSON TXT