ECTOENZYMES AS SITES OF PEPTIDE REGULATION

The ectoenzyme-mediated metabolism of neuropeptides may be an importan t regulatory site of peptide-mediated activity. These membrane-bound, extracellularly oriented peptidases are not only responsible for inact ivating peptide substrates, but also lead to the formation of meta bel ie fragments. Peptide fragments formed after enzymatic proteolysis hav e been shown to display novel bioactivity as a consequence of a shift in receptor selectivity. This example of nervous system plasticity thr ough peptide biotransformation can have multiple consequences. Central ly acting drugs have been shown to have profound effects on peptide-me diated systems throughout the brain and spinal cord including a differ ential alteration in ectoenzyme activity and ectoenzyme-mediated metab olism of neuropeptides. In this review, Tom Davis and Chris Konkoy sug gest that the modulation of ectoenzyme-mediated peptide metabolism rep resents an additional level at which the concentration of extracellula r neuropeptides, and thus peptide-mediated transmission, can be regula ted.