TAILIEUCHUNG - Báo cáo khoa học: The lactate dehydrogenases encoded by the ldh and ldhB genes in Lactococcus lactis exhibit distinct regulation and catalytic properties ) comparative modeling to probe the molecular basis

Lactococcus lactisFI9078, a construct carrying a disruption of theldh gene, converted approximately 90% of glucose into lactic acid, like the parental strain MG1363. This unexpected lactate dehydrogenase activity was puri-fied, andldhB was identified as the gene encoding this protein. The activa-tion of ldhB was explained by the insertion of an IS905-like element that created a hybrid promoter in the intergenic region upstream ofldhB. | ễFEBS Journal The lactate dehydrogenases encoded by the Idh and IdhB genes in Lactococcus lactis exhibit distinct regulation and catalytic properties - comparative modeling to probe the molecular basis Paula Gaspar1 Ana R. Neves1 Claire A. Shearman2 Michael J. Gasson2 Antonio M. Baptista1 David L. Turner1 Claudio M. Soares1 and Helena Santos1 1 Institute de Tecnologia Quimica e Biologica Universidade Nova de Lisboa Oeiras Portugal 2 Institute of Food Research Norwich Research Park UK Keywords enzyme kinetics IdhB lactate dehydrogenase Lactococcus lactis protein modeling Correspondence H. Santos Instituto de Tecnologia Quimica e Biologica Universidade Nova de Lisboa Rua da Quinta Grande 6 Apt 127 2780-156 Oeiras Portugal Fax 351 21 4428766 Tel 351 21 4469828 E-mail santos@ Database The nucleotide sequence of the IdhB gene from L. lactis MG1363 has been submitted to the GenBank database under the accession number AY236961 Received 2 August 2007 revised 20 September 2007 accepted 21 September 2007 doi Lactococcus lactis FI9078 a construct carrying a disruption of the Idh gene converted approximately 90 of glucose into lactic acid like the parental strain MG1363. This unexpected lactate dehydrogenase activity was purified and IdhB was identified as the gene encoding this protein. The activation of IdhB was explained by the insertion of an IS905-like element that created a hybrid promoter in the intergenic region upstream of ldhB. The biochemical and kinetic properties of this alternative lactate dehydrogenase LDHB were compared to those of the ldh-encoded enzyme LDH purified from the parental strain. In contrast to LDH the affinity of LDHB for NADH and the activation constant for fructose 1 6-bisphosphate were strongly dependent on pH. The activation constant increased 700-fold whereas the Km for NADH increased more than 10-fold in the pH range . The two enzymes also exhibited different pH profiles for maximal .

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