Earthworm pre-procarboxypeptidase: a copper responsive enzyme

This paper describes the identification and molecular cloning of the earthw orm metalloenzyme pre-procarboxypeptidase. It was possible to approximate t he putative pre-pro cleavage sites, which after removal activates a 35.7 kD a mature peptide with a length of 317 amino acids. The primary, secondary a nd predicted tertiary structure of the mature chain is highly homologous to other carboxypeptidases from diverse phylogenetic origin. Using a fully qu antitative PCR, we were able to assess relative expression of this gene in earthworms exposed to different heavy metal contaminated substrates. In sum mary, cadmium on its own or in combination with lead and zinc, did not trig ger transcriptional up-regulation of carboxypeptidase. In contrast, copper exposed earthworms were assessed to have a 4-fold increase in carboxypeptid ase transcript numbers. A hypothetical model is presented to explain how th e exposure to heavy metals may influence transcriptional control and/or fun ction of this enzyme. Finally, the significance of these observations in te rms of risk assessment and biomonitoring of contaminated soils is discussed .