The homoserine kinase (HK) gene was cloned from Brevibacterium lactofermentum M-15, a threonine-producing mutant. Then, a trimethoprim-resistant hybrid plasmid pAJ2 12 expressing the HK gene was constructed. A threonine-producing recombinant strain harboring pAJ210, a chloramphenicol-resistant plasmid on which homoserine dehydrogenase (HD) gene was cloned, was transformed further with the obtained HK-expressing plasmid pAJ2 12. Plasmids pAJ2 10 and pAJ212were compatible in B. lactofermentum because these two plasmids were derived from two different cryptic plasmids, PHM1519 and pAM330respectively. Co-existence of the cloned HDand HKgenes in M-15 resulted in more than a 30% increase of threonine production (33 g/liter) and a decrease of the by-products (lysine and homoserine) as compared with M-15 carrying HD recombinant plasmid alone. The activities of HDand HKin the strain harboring both HD-and HK-recombinant plasmids were elevated markedly by gene dosage effect, which brought about the apparent increase in threonine production.
2-Nitropropane dioxygenase, purified to homogeneity by an improved method from a yeast, Hansenula mrakii, has a molecular weight of 42,000, and consists of a single polypeptide. The enzyme contains 1 mol of FADper mol of enzyme. The iron protein associated with previous preparations was removed by the present purification procedures. The enzymecatalyzes the oxygenative denitrification of anionic nitroalkanes much more effectively than that of the neutral ones with the optimumpH of 6.5. The Michaelis constants for the anionic substrates are as follows: 2-nitropropane, 1.61 him; 1-nitropropane, 3.23 him; nitroethane, 3.13 mM, and 3-nitro-2-butanol, 0.59mM. Various organic nitro compounds occur in nature, and most of them (e.g. chloramphenicol) are physiologically active.2) Several nitro compounds are widely used as intermediary raw materials and solvents in the chemical industry and also as a fuel for rockets.3
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.