cystathionine + H2O -- -ketobutyrate + cysteine + NH3
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According to Nomura . (1987) QL-5, aspartate kinase was sensitive to feed back inhibition in the simultaneous presence of L-lysine and L-threonine. The simultaneous addition of these two s (1mM each) produced about 60% inhibition. The inhibition was reduced to about 40% by dialysis. Similarly, in L-lysine production by resting cells, the simultaneous addition of these two s (1mM each) produced 35% inhibition and dialysis reduced the inhibition to 12%. In dialysis cultures the lag-phase was shortened and cell mass increased, as compared to non dialysis culture. Moreover, in dialysis cultures, L-lysine was produced earlier and the maximum productivity of L-lysine (1.50 g L-1) was obtained in 6 through 10 hrs cultivation. Yokota and Shiio (1988), studied the effect of reduced citrate synthetase activity and feedback resistant phosphoenol pyruvate carboxylase on L-lysine productivities. Aspartokinase and S-2 aminoethyl cystein (AEC) resistant mutant plus threonine auxotroph of was found to produced more than 40 gL-1 of L-lysine as its HCl salt in the medium containing 10 % glucose. In particular, strain No. 664-7 with normally active and completely feed back resistant. AK produced 45g L-1 of L-lysine, HCl. A homoserine dehydrogenase-defective mutant (HD), H-3-4, with low level citrate synthetase and phosphoenol pyruvate carboxylase character also showed higher L-lysine productivity, 41 g / L, than the HD mutant, H1013, which was derived directly from the wild strain. Thus it was concluded that the low level citrate synthetase and phosphoenol pyruvate carboxylase character were effective for the enhancement of the L-lysine productivities of both aspartokinase resistant and HD type producers. Smekal . (1988) studied the control of L-lysine biosynthesis with chromogene mutants of Species M-27. They found 43 to 49 g L-lysine per liter in 96 hours with conversion of 45 to 49%.
(3) phenylalanine, Tyrosine, Tryptophan
Current availability of many complete genomes gives an opportunity to compare genes encoding one metabolic pathway and their regulation in a variety of bacteria. The comparative analysis is a powerful approach for prediction of the conserved RNA secondary structures and detection of novel regulatory RNA elements upstream of co-regulated genes in bacterial genomes (). In particular, highly conserved RFN, THI and B12 elements were identified in various bacteria upstream of genes involved in the biosynthesis of riboflavin, thiamin and cobalamin, respectively (–). In such studies, analysis of complementary substitutions in aligned sequences is used to construct a single conserved structure of an RNA regulatory element.
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