In vitro regulation of rat liver L-threonine deaminase by different effectors.
The regulation of liver L-threonine deaminase by different effectors--bile acids, bile pigments and monocarbon molecules--was investigated. Total inhibition of the enzyme was observed with physiological concentrations of bile acids and biliverdin. Purely competitive inhibition of the holoenzyme by several monocarbon molecules was demonstrated; the mechanism was partially competitive for bicarbonate. Inhibition was more pronounced in the case of the dialyzed enzyme. From the higher Km values for pyridoxal-5'-phosphate (PLP), obtained in the presence of the inhibitors, the results are explained on the basis of interference in the association reaction: apoprotein + PLP----holoenzyme. The various effects determined by bicarbonate may play a specific role in vivo since they occur at physiological concentrations of this compound.
Pagani
R
R
Institute of Biological Chemistry, University of Siena, Italy.
Leoncini
R
R
Terzuoli
L
L
Guerranti
R
R
Marinello
E
E
D000818:Animals; D001639:Bicarbonates / Q000494:pharmacology; D001647:Bile Acids and Salts / Q000494:pharmacology; D001663:Bilirubin / Q000494:pharmacology; D001664:Biliverdine / Q000494:pharmacology; D002264:Carboxylic Acids / Q000494:pharmacology; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D008297:Male; D011732:Pyridoxal Phosphate / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D013912:Threonine / Q000378:metabolism; D013913:Threonine Dehydratase / Q000037:antagonists & inhibitors / Q000302:isolation & purification / Q000378:metabolism*
D001639:Bicarbonates; D001647:Bile Acids and Salts; D002264:Carboxylic Acids; D013912:Threonine; D011732:Pyridoxal Phosphate; D013913:Threonine Dehydratase; D001664:Biliverdine; D001663:Bilirubin