Aminopeptidase-B in the rat testes: isolation, functional properties and cellular localization in the seminiferous tubules.
An aminopeptidase of the B-type, with an apparent M(r) 72,000 and pI = 4.9, was isolated from rat testes and characterized. The enzyme was able to remove only Arg and/or Lys residues from L-amino acid beta-naphthylamide derivatives and from the N-terminus of several peptides. No cleavage occurred in the case of Arg-Pro bonds as found in bradykinin and substance P. The enzyme was sensitive to cysteinyl reagents and to aminopeptidase inhibitors, such as bestatin, amastatin and arphamenines A and B. The aminopeptidase activity, tested with L-Arg beta-naphthylamide and with Arg0-Met-enkephalin as substrates, was inhibited by o-phenanthroline, and restored by Zn2+ suggesting its metallopeptidase character. The partial characterization of an aminopeptidase-B activity in rat brain cortex identified a protein which is biochemically and immunologically related to the testis enzyme. By immunohistochemistry, the aminopeptidase-B was found to be particularly abundant in the seminiferous tubules at late stages of spermatogenesis and was clearly detected in a restricted area of elongated spermatids. Remarkably, the enzyme was observed to concentrate massively in the residual bodies. Since this aminopeptidase-B was able in vitro to trim out N-terminal Arg and/or Lys residues from peptides mimicking processing intermediates, it is proposed that this enzyme may be involved in propeptide and proprotein processing mechanisms in the course of spermatid differentiation.
Cadel
S
S
Laboratoire de Biochimie des Signaux Régulateurs Cellulaires et Moléculaires, Université Pierre et Marie Curie, Unité de Recherches Associée au Centre National de la Recherche Scientifique 1682, Paris, France.
Pierotti
A R
AR
Foulon
T
T
Créminon
C
C
Barré
N
N
Segrétain
D
D
Cohen
P
P
D000595:Amino Acid Sequence; D000626:Aminopeptidases / Q000037:antagonists & inhibitors / Q000302:isolation & purification* / Q000378:metabolism; D000818:Animals; D015153:Blotting, Western; D002412:Cations; D005455:Fluorescent Antibody Technique; D006863:Hydrogen-Ion Concentration; D007124:Immunoenzyme Techniques; D007700:Kinetics; D008297:Male; D008969:Molecular Sequence Data; D010618:Phenanthrolines / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D012671:Seminiferous Tubules / Q000201:enzymology*; D013094:Spermatozoa / Q000201:enzymology; D013379:Substrate Specificity; D013737:Testis / Q000201:enzymology*; D015032:Zinc / Q000494:pharmacology
D002412:Cations; D010618:Phenanthrolines; D000626:Aminopeptidases; C019721:aminopeptidase B; D015032:Zinc; C025205:1,10-phenanthroline