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Báo cáo khoa học: Control analysis as a tool to understand the formation of the las operon in Lactococcus lactis

In Lactococcus lactisthe enzymes phosphofructokinase (PFK), pyruvate kinase (PK) and lactate dehydrogenase (LDH) are uniquely encoded in the las operon. We used metabolic control analysis to study the role of this organization. Earlier studies have shown that, at wild-type levels, LDH has no control over glycolysis and growth rate, but high negative control over formate production (C Jformate LDH ¼ 1:3). | iFEBS Journal Control analysis as a tool to understand the formation of the las operon in Lactococcus lactis Brian Koebmann Christian Solem and Peter Ruhdal Jensen MicrobialPhysiology and Genetics BioCentrum-DTU TechnicalUniversity of Denmark Kgs Lyngby Denmark Keywords glycolysis Lactococcus las metabolic control analysis operon Correspondence P. R. Jensen MicrobialPhysiology and Genetics BioCentrum-DTU Technical University of Denmark Building 301 DK-2800 Kgs. Lyngby Denmark Tel 45 4525 2510 Fax 45 4593 2809 E-mail prj@biocentrum.dtu.dk Received 23 December 2004 revised 28 February 2005 accepted 9 March 2005 doi 10.1111 j.1742-4658.2005.04656.x In Lactococcus lactis the enzymes phosphofructokinase PFK pyruvate kinase PK and lactate dehydrogenase LDH are uniquely encoded in the las operon. We used metabolic control analysis to study the role of this organization. Earlier studies have shown that at wild-type levels LDH has no control over glycolysis and growth rate but high negative control over formate production CldH _1.3 . We found that PFK and PK exert no control over glycolysis and growth rate at wild-type enzyme levels but both enzymes exert strong positive control on the glycolytic flux at reduced activities. PK exerts high positive control over formate cPfK ate 0.9 1-1 and acetate production cPaKtate 0.8 1.0 whereas PFK exerts no control over these ffluxes at increased expression. Decreased expression of the entire las operon resulted in a strong decrease in the growth rate and glycolytic flux at 53 expression of the las operon glycolytic flux was reduced to 44 and the flux control coefficient increased towards 3. Increased las expression resulted in a slight decrease in the glycolytic flux. At wild-type levels control was close to zero on both glycolysis and the pyruvate branches. The sum of control coefficients for the three enzymes individually was comparable with the control coefficient found for the entire operon the strong positive control exerted by .