Expression and properties of human liver beta-ureidopropionase

A cDNA encoding beta -ureidopropionase (BUP) was isolated from a human live r cDNA library, expressed in E, coli, and purified from the culture extract , The 2,006 bp cDNA contained a 1,152 bp open reading frame encoding a prot ein of 384 amino acids with a molecular weight of 43,165 Da. The subunit mo lecular weight of the enzyme expressed was about 43,000 Da. The enzyme was inhibited by 1 mM propionate, but not by 10 mM beta -alanine. Chemical anal ysis of the purified human BUP showed 0.54 zinc atoms per subunit, and the sequence of BUP cDNA contained one putative zinc-binding site motif, The pu rified enzyme had a pI of 5.65, and exhibited positive cooperativity with N -carbamoyl-beta -alanine as the substrate with a Hill coefficient 2.0, Thes e properties of human BUP, except: the inhibition by beta -alanine, were si milar to the rat liver purified enzyme. beta -Alanine inhibits rats BUP act ivity. The complex regulatory function and the negative cooperative mechani sm of BUP by beta -alanine have been observed in rats. This kind of mechani sm may not exist: in humans, because beta -alanine did not inhibit human BU P.