PURIFICATION AND CHARACTERIZATION OF CATABOLIC MANNOPINE CYCLASE ENCODED BY THE AGROBACTERIUM-TUMEFACIENS TI PLASMID PTI15955

Catabolic mannopine (MOP) cyclase encoded by certain Agrobacterium Ti and Ri plasmids lactonizes MOP to agropine (AGR). The enzyme, purified to homogeneity from a recombinant clone, has a molecular mass of 45 k Da as measured by sodium dodecyl sulfate-polyacrylamide gel electropho resis and size exclusion chromatography. The enzyme catalyzed the lact onization of MOP to AGR without the need for any cofactors. The enzyme also converted AGR to MOP with the lactonizing activity being predomi nant over the reverse reaction. MOP cyclase is specific for imine conj ugates of D-hexose and L-glutamine and was not inhibited by sugars or amino acids. The enzyme lactonized deoxyfructosyl glutamine, a natural intermediate of MOP synthesis and catabolism, to a product indistingu ishable from chrysopine, a newly discovered crown gall opine. The enzy me also lactonized N-1-(1,2-dideoxy-D-mannityl)-L-glutamine, indicatin g that a hydroxyl group at carbon atom 2 of the sugar moiety is not re quired for the enzymatic reaction.