Effects of amino acids on Thiobacillus acidophilus. II. Threonine deaminase.
Biosynthetic L-threonine deaminase was partially purified 73-fold with a 60% recovery from Thiobacillus acidophilus by ammonium sulfate fractionation and by Sepharose 6B-C1 chromatography. The optimal pH for enzyme activity was between 9.0 and 10.0 and no optimal pH shift was observed in the presence of L-isoleucine, an inhibitor. The enzyme was effectively inhibited by L-isoleucine and showed homotropic interaction only in the presence of L-isoleucine. Kinetic studies indicate that there are at least two threonine binding sites and at least two isoleucine binding sites. The Km for threonine is 2.5 x 10(-3) M. The inhibition due to isoleucine is reversed by low concentrations of L-valine. L-Valine at high concentration acts as a substrate analogue and competitively inhibits L-threonine binding at the active site; the K1 is 1.6 x 10(-2) M.
D001665:Binding Sites; D007532:Isoleucine / Q000494:pharmacology; D013237:Stereoisomerism; D013855:Thiobacillus / Q000201:enzymology*; D013912:Threonine / Q000378:metabolism; D013913:Threonine Dehydratase / Q000302:isolation & purification / Q000378:metabolism*; D014633:Valine / Q000494:pharmacology
D007532:Isoleucine; D013912:Threonine; D013913:Threonine Dehydratase; D014633:Valine