Bovine pituitary pyrrolidonecarboxylyl peptidase.

Abstract

An enzyme has been obtained from bovine pituitary tissue which hydrolyzes L-pyrrolidonecarboxylyl- L-alanine, but not L-glutamyl-Lalanine. The enzyme was identified in whole pituitary homogenates, in 100,000 × g supernatant fraction of whole pituitaries and in anterior pituitary homogenates. After partial purification by ammonium sulfate precipitation and gel filtration, the enzyme was found to have a Km of 2.3 × 10–4M and to have maximal activity at pH 7.3. Like the Pseudomonas fluorescens pyrrolidonecarboxylyl peptidase prepared by Doolittle and coworkers, this enzyme is sulfhydryl-dependent and unstable in solution, but may be stabilized ∧ with the inhibitor 2-pyrrolidinone. The pituitary enzyme has been shown to cleave L-2-pyrrolidone- 5-carboxylic acid from the NH2-terminal position of synthetic thyrotropin-releasing factor and thus may have a degradative function related to the regulatory system controlling release of thyroid-stimulating hormone from the anterior pituitary. Evidence has been obtaine...