Catalysis of slow C-terminal processing reactions by carboxypeptidase H

D. G. Smyth, K. Maruthainar, N. J. Darby, Lloyd D. Fricker

Research output: Contribution to journalArticle

37 Citations (Scopus)

Abstract

A hypothesis was examined that carboxypeptidase H (CpAse H), which is known to catalyse the release of lysine and arginine from the C-terminus of peptides, can also release histidine, tyrosine, and phenylalanine. Synthetic peptides terminating in -His-Lys or -Tyr-Lys were used as model substrates for the enzyme and amino acid analysis was employed to detect release of the terminal amino acids. With N-acetyl-β-Ala-Asn-Ala-His-Lys and N-acetyl-β-Ala-Asn-Ala-Tyr-Lys, which correspond to intermediates in the processing of porcine and human β-endorphin, lysine was removed rapidly and quantitatively but no release of histidine or tyrosine could be detected. To allow more sensitive analysis, radiolabeled substrates were employed and the amounts of the products formed on incubation with CpAse H were determined after separation by ion-exchange chromatography. With 125I-D-Tyr-Ala-His-Lys-Lys as substrate at pH 5.7, very small amounts of D-Tyr-Ala were released; the main product was D-Tyr-Ala-His. At pH 5.0 the release of histidine from 125I-D-Tyr-Ala-His took place 6,000 times more slowly than the release of lysine from 125I-D-Tyr-ala-Lys. When the tripeptides were incubated at pH 5 with porcine pituitary secretory granules, the lysine was released rapidly but no release of histidine could be detected. The results demonstrate that CpAse H catalyses the release of C-terminal histidine with great difficulty. Evidence is also presented with CpAse H catalyses a similar slow reaction in converting α-neo-endorphin to β-neo-endorphin, which involves removal of lysine from a Pro-Lys sequence. These very slow reactions provide an explanation for the incomplete processing that is observed with neuropeptides terminating in histidine, tyrosine, or phenylalanine or in prolyllysine.

Original languageEnglish (US)
Pages (from-to)489-493
Number of pages5
JournalJournal of Neurochemistry
Volume53
Issue number2
StatePublished - 1989

Fingerprint

Carboxypeptidase H
Catalysis
Histidine
Lysine
Endorphins
Processing
Tyrosine
Phenylalanine
tyrosyl-lysine
Substrates
Swine
Amino Acids
Peptides
Ion Exchange Chromatography
Secretory Vesicles
Chromatography
Neuropeptides
Arginine
Ion exchange
Enzymes

ASJC Scopus subject areas

  • Biochemistry
  • Cellular and Molecular Neuroscience

Cite this

Catalysis of slow C-terminal processing reactions by carboxypeptidase H. / Smyth, D. G.; Maruthainar, K.; Darby, N. J.; Fricker, Lloyd D.

In: Journal of Neurochemistry, Vol. 53, No. 2, 1989, p. 489-493.

Research output: Contribution to journalArticle

Smyth, DG, Maruthainar, K, Darby, NJ & Fricker, LD 1989, 'Catalysis of slow C-terminal processing reactions by carboxypeptidase H', Journal of Neurochemistry, vol. 53, no. 2, pp. 489-493.
Smyth, D. G. ; Maruthainar, K. ; Darby, N. J. ; Fricker, Lloyd D. / Catalysis of slow C-terminal processing reactions by carboxypeptidase H. In: Journal of Neurochemistry. 1989 ; Vol. 53, No. 2. pp. 489-493.
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