Growth inhibition activity of imazosulfuron, 1-(2-chloroimidazo [1,2-a] pyridin-3-ylsulfonyl)-3-(4, 6-dimethoxypyrimidin-2-yl)urea, against excised pea and soybean roots was investigated. Fifty percents growth inhibition concentrations of Imazosulfuron (I50) against pea and soybean roots were 17.6 and 54.2 ppb, respectively. When the excised pea roots were incubated in the culture medium containing 25 ppb of Imazosulfuron and 1mM of either branched-chain amino acids or intermediates of their biosynthetic pathways, the growth inhibition activity of excised roots was alleviated by the combination of isoleucine and valine or a-ketoisovalerate and a-keto-f3-methyl-n-valerate. These findings suggest that Imazosulfuron exhibits inhibition of acetolactate synthase which catalyses the biosynthetic pathways of branchedchain amino acids. Metabolic fate of Imazosulfuron in excised pea roots was studied using the 14C-labeled compounds. Imazosulfuron was predominantly demethylated to afford a monodemethyl derivative (HMS) in the roots, and hydrolytically cleaved at the sulfonylurea bond to give a sulfonamide (IPSN) and an aminopyrimidine (ADPM) in the culture medium. Since HMS did not inhibit the growth of excised roots, metabolic fate of Imazosulfuron is involved in a selectivity between plants.

Lysyl-tRNA synthetase [L-lysine:tRNA(Lys)ligase (AMP forming); EC 6.1.1.6] was purified from Bacillus stearothermophilus NCA1503 approximately 1,100-fold to homogeneity in PAGE. The enzyme is a homodimer of M(r) 57,700 x 2. The molar absorption coefficient, epsilon, at 280 nm is 71,600 M-1.cm-1 at pH8.0. Enzyme activity in the tRNA aminoacylation reaction and the ATP-PPi exchange reaction increases up to 50 degrees C at pH 8.0, but is lost completely at 70 degrees C. The pH-optima of the two reactions are 8.3 at 37 degrees C. In the tRNA aminoacylation reaction, the Km values for L-lysine and ATP are 16.4 and 23.2 muM, respectively, and in the ATP-PPi exchange reaction, the Km values for L-lysine and ATP are 23.6 and 65.1 muM, respectively at 37 degrees C, pH 8.0. Interaction of either L-lysine or ATP with the enzyme has been investigated by using as a probe the ligand-induced quenching of protein fluorescence and by equilibrium dialysis. These static analyses, as well as the kinetic analysis of the L-lysine dependent ATP-PPi exchange reaction indicate that the binding mode of L-lysine and ATP to the enzyme is sequential ordered (L-lysine first). The interaction of lysine analogues with the enzyme has also been investigated.

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