L-serine dehydratase from Arthrobacter globiformis.
1. L-Serine dehydratase (EC 4.2.1.13) was purified 970-fold from glycine-grown Arthrobacter globiformis to a final specific activity of 660micronmol of pyruvate formed/min per mg of protein. 2. The enzyme is specific for L-serine; D-serine, L-threonine and L-cysteine are not attacked. 3. The time-course of pyruvate formation by the purified enzyme, in common with enzyme in crude extracts and throughout the purification, is non-linear. The reaction rate increases progressively for several minutes before becoming constant. The enzyme is activated by preincubation with L-serine and a linear time-course is then obtained. 4. The substrate-saturation curve for L-serine is sigmoid. The value of [S]0.5 varies with protein concentration, from 6.5mM at 23microng/ml to 20mM at 0.23microng/ml. The Hill coefficient remains constant at 2.9.5 The enzyme shows a non-specific requirement for a univalent or bivalent cation. Half-maximal activity is produced by 1.0mM-MgCl2 or by 22.5mM-KCl. 6. L-Cysteine and D-serine act as competitive inhibitors of L-serine dehydratase, with Ki values of 1.2 and 4.9mM respectively. L-Cysteine, at higher concentrations, also causes a slowly developing irreversible inhibition of the enzyme. 7. Inhibition by HgCl2 (5micronM)can be partially reversed in its initial phase by 1mM-L-cysteine, but after 10 min it becomes irreversible. 8. In contrast with the situation in all cell-free preparations, toluene-treated cells of A. globiformis form pyruvate from L-serine at a constant rate from the initiation of the reaction, show a hyperbolic substrate-saturation curve with an apparent Km of 7mM and do not require a cation for activity.
D001173:Arthrobacter / Q000187:drug effects / Q000201:enzymology*; D001431:Bacteriological Techniques; D002474:Cell-Free System; D002850:Chromatography, Gel; D003545:Cysteine / Q000494:pharmacology; D004573:Electrolytes / Q000494:pharmacology; D004591:Electrophoresis, Polyacrylamide Gel; D007700:Kinetics; D012695:L-Serine Dehydratase / Q000037:antagonists & inhibitors / Q000302:isolation & purification / Q000378:metabolism*; D008628:Mercury / Q000494:pharmacology; D011773:Pyruvates / Q000096:biosynthesis; D012694:Serine / Q000494:pharmacology; D014050:Toluene / Q000494:pharmacology
D004573:Electrolytes; D011773:Pyruvates; D014050:Toluene; D012694:Serine; D012695:L-Serine Dehydratase; D008628:Mercury; D003545:Cysteine