Characterization of an islet carboxypeptidase B involved in prohormone processing.

Robert Mackin, B. D. Noe

Research output: Contribution to journalArticle

21 Citations (Scopus)

Abstract

An islet carboxypeptidase B-like enzyme (CP B) has been identified and characterized in secretory granules of anglerfish islets. By employing several different column chromatography methods (gel filtration, ion exchange, and hydroxylapatite), it was determined that the islet secretory granules contained only one detectable CP B. This enzyme is present in both secretory granule- and microsome-enriched subcellular fractions and is membrane associated at pH 5.2. The specific activity of the islet CP B was approximately 4-fold higher in the secretory granule- and microsome-enriched subcellular fractions than in the lysosome-enriched fraction. It is a metallo-enzyme that is stimulated by Co++, and has a pH optimum in the range of 5.2-6.2. The isoelectric point of the islet CP B is at pH 4.9. The enzyme is a glycoprotein and has an approximate molecular size of Mr 30,000 by gel filtration. The substrate analogs guanidinoethylmercaptosuccinic acid, guanidinopropylsuccinic acid, and aminopropylmercaptosuccinic acid competitively inhibited the islet CP B with inhibition constant (Ki) values of 23, 21, and 230 nM, respectively. In experiments employing purified prohormone substrates it was demonstrated that the action of a CP B-like enzyme was required for the complete processing of anglerfish proinsulin and prosomatostatin-II. These results indicate that the anglerfish islet CP B is involved in prohormone processing and has properties which are very similar to those of enkephalin convertase.

Original languageEnglish
Pages (from-to)457-468
Number of pages12
JournalEndocrinology
Volume120
Issue number2
StatePublished - Feb 1987
Externally publishedYes

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Carboxypeptidase B
Enzymes
Secretory Vesicles
Subcellular Fractions
Microsomes
Gel Chromatography
Carboxypeptidase H
Proinsulin
Ion Exchange
Isoelectric Point
Durapatite
Lysosomes
Glycoproteins

All Science Journal Classification (ASJC) codes

  • Endocrinology
  • Endocrinology, Diabetes and Metabolism

Cite this

Characterization of an islet carboxypeptidase B involved in prohormone processing. / Mackin, Robert; Noe, B. D.

In: Endocrinology, Vol. 120, No. 2, 02.1987, p. 457-468.

Research output: Contribution to journalArticle

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