抄録
1. Effect of 13 amino acids on enzymes in the pathway from aspartate to threonine in Brevibacterium flavum were estimated.
2. Simultaneous addition of threonine and lysine (10mM each) caused 56% inhibition of aspartate kinase [EC 2. 7. 2. 4], whereas addition of either amino acid did not cause significant inhibitory effect.
3. L-Aspartate-β-semialdehyde dehydrogenase [EC 1. 2. 1. 11] was scarcely inhibited by amino acids of aspartate family. Serine inhibited the activity by about 40% at a concentration of 10mM.
4. Homoserine dehydrogenase [EC 1. 1. 1. 3] was competitively inhibited by threonine and by isoleucine. 3.3mM of threonine inhibited the activity completely in the forward and reverse reaction, and 10mM of isoleucine inhibited the activity by about 90% in the forward reaction, and by about 60% in the reverse reaction.
5. Homoserine kinase [EC 2. 7. 1. 39] was inhibited by threonine in the extent of 60% at 30mM. Other amino acids of aspartate family showed slightly inhibitory effect at 10mM.
6. Threonine synthase [EC 4. 2. 99. 2] was scarcely inhibited by amino acids of aspartate family. Cysteine and glutathione showed 100% inhibition at 10mM revealed by measurement of the determination of phosphohomoserine disappearance.
