Improvement of L(+)-Lactic Acid Production of Rhizopus Oryzae by Low-Energy Ions and Analysis of Its Mechanism

摘要

The wild type strain Rhizopus oryzae PW352 was mutated by means of nitrogen ionimplantation (15 keV,7.8×10^(14)～2.08×10^(15) ions/cm^2) to find an industrial strain with a higherL(+)-laetic acid yield,and two mutants RE3303 and RF9052 were isolated.In order to discussthe mechanism primarily,Lactate Dehydrogenase of Rhizopus oryzae was studied.While the twomutants produced L(+)-laetic acid by 75% more than the wild strain did,their specific activityof Lactate Dehydrogenase was found to be higher than that in the wild strain.The optimumtemperature of Lactate Dehydrogenase in Rhizopus oryzae RF9052 was higher.Compared tothe wild strain,the Michaelis constant (Km) value of Lactate Dehydrogenase in the mutantswas changed.All these changes show that L(+)-lactic acid production has a correlation withthe specific activity of Lactate Dehydrogenase.The low-energy ions,implanted into the strain,may improve the specific activity of Lactate Dehydrogenase by influencing its gene structure andprotein structure.