EVIDENCE THAT A DEFERRIOXAMINE-B DEGRADING ENZYME IS A SERINE-PROTEASE

Siderophores are organic biomolecules synthesized by a wide variety of microbes. The molecules sequester ferric ion from environments where it is present at extremely low concentrations. Siderophores are of con sequence with respect to microbial nutrition, pathogenicity, virulence , and microbe-plant interactions. How siderophores are degraded and re turned to the carbon and nitrogen cycles is not well understood. The c atalytic activity of an enzyme from a bacterium that degrades the side rophore deferrioxamine B has been examined. While the degradation of d eferrioxamine B is sensitive to sulfhydryl and metal moiety inhibitors , the data presented is most consistent with the hypothesis that the e nzyme uses a hydroxyl moiety (serine peptidase) to catalyze the degrad ation of deferrioxamine B. If sulfhydryl and metal inhibitors are simu ltaneously present at concentrations that when alone only partially in hibit the enzyme, the enzyme is unable to catalyze deferrioxamine B di ssimilation. Analysis of the inhibitor experiments conducted led to th e conclusion that the deferrioxamine B degrading enzyme is a serine-pe ptidase-like enzyme that needs calcium ions and sulfhydryl groups to b e fully activated or stabilized. The knowledge of the catalytic moieti es of the enzyme will be exploited to purify the enzyme.