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Pronunciation: pas'mak-er


  1. Biologically, any rhythmic center that establishes a pace of activity.
  2. An artificial regulator of rate activity.
  3. In chemistry, the substance of which the rate of reaction sets the pace for a series of chain reactions; the rate-limiting reaction itself, in a metabolic pathway, the enzyme catalyzing the slowest or rate-limiting reaction in that pathway.

[L. passus, step, pace]

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© Copyright 2018 Wolters Kluwer. All Rights Reserved. Review Date: Sep 19, 2016.