SUMMARY: Two 2-hydroxy-6-oxohepta-2,4-dienoate (HOD) hydrolases have been purified to homogeneity from ATCC 17707. One, HODHII, is encoded by the TOL-like plasmid, pRA1000, and the other, HODHI, is chromosomally-encoded. HODHI and HODHII have an of 104 × 10 and 116 × 10, respectively, and both are dissociated by SDS into three subunits of equal size which are not linked by disulphide bonds. Both hydrolases are active against a similar range of substrates formed by the action of catechol 2,3-oxygenases, generally being more active against substrates formed from 3-alkyl- rather than 4-alkyl-substituted catechols. HODHI and HODHII had similar values for HOD, but HODHI had a significantly lower value for, and a higher activity against, 2-hydoxymuconic semialdehyde than HODHII. It was shown by immunodiffusion studies that the two hydrolases were immunologically distinct and that HODHI had no common antigenic determinants with HOD hydrolases from the strains NCIB 9865, NCIB 10015 and mt-2; HODHII gave a line of identity with antiserum to the hydrolase from NCIB 9865. A comparison of the physico-chemical properties of HODHI and HODHII with the same properties of the HOD hydrolases from the three strains demonstrated several similarities between the five HOD hydrolases which have been purified.


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