SUMMARY: PP3 grew on -2-monochloropropionate (2MCPA) with a release of chloride ions consistent with the dechlorination of both isomers. The organism grew on either - or -2MCPA. Dehalogenase activity in cell-free extracts showed that both - and -2MCPA were dehalogenated. PP3 contains two dehalogenases, and studies with the separated enzymes revealed that the fraction I enzyme used both - and -2MCPA, the rate of dechlorination of -2MCPA being 80% of the rate of -2MCPA dechlorination. The product of the reaction, lactate, retained the same optical configuration as the substrate provided. The fraction II dehalogenase also dechlorinated - and -2MCPA, with the same difference in rates as for the fraction I dehalogenase, but the lactates produced were of the opposite configuration to their precursors. The two dehalogenases showed further differences with respect to inhibition by two sulphydryl-blocking agents, -ethylmaleimide and -chloromercuribenzoate. Fraction I dehalogenase was considerably more sensitive to these two reagents compared with the fraction II dehalogenase. Dithiothreitol partially protected the fraction I dehalogenase from -ethylmaleimide inhibition. The results are discussed in terms of the possible evolutionary relationships of the two dehalogenases.


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