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Regular Article |
a Cátedras de Química Biológica, Facultades de Ciencias Médicas and
b Ciencias Exactas, Físicas y Naturales, Universidad Nacional de Córdoba, Córdoba, Argentina
ABSTRACT
Dramatic inhibition of trypsin activity by rat caltrin and guinea pig caltrin I was spectrophotometrically demonstrated using the artificial substrate benzoylarginyl ethyl ester. Approximately 6% and 21% of residual proteolytic activity was recorded after preincubating the enzyme with 0.22 and 0.27 µM rat caltrin and guinea pig caltrin I, respectively. Reduction and carboxymethylation of the cysteine residues abolished the inhibitor activity of both caltrin proteins. Rat caltrin and guinea pig caltrin I show structural homology with secretory trypsin/acrosin inhibitor proteins isolated from boar and human seminal plasma and mouse seminal vesicle secretion and share a fragment of 13 amino acids of almost identical sequence (DPVCGTDGH/K/ITYG/AN), which is also present in the structure of Kazal-type trypsin inhibitor proteins from different mammalian tissues. Bovine, mouse, and guinea pig caltrin II, three caltrin proteins that have no structural homology with rat caltrin or guinea pig caltrin I, lack trypsin inhibitor activity. Rat caltrin, guinea pig caltrin I, and the mouse seminal vesicle trypsin inhibitor protein P12, which also inhibits Ca2+ uptake into epididymal spermatozoa (mouse caltrin I), bound specifically to the sperm head, on the acrosomal region, as detected by indirect immunofluorescence. They also inhibited the acrosin activity in the gelatin film assay. Caltrin I may play an important role in the control of sperm functions such as Ca2+ influx in the acrosome reaction and activation of acrosin and other serine-proteases at the proper site and proper time to ensure successful fertilization.
First decision: 4 November 1999.
1 This work was supported by a grant from the Agencia Nacional de Promoción Científica y Tecnológica (PICT 01225, Préstamo BID 802/OC-AR) and grants from Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Consejo de Investigaciones Científicas y Tecnológicas de la Provincia de Córdoba (CONICOR), and Secretaría de Ciencia y Tecnología de la Universidad Nacional de Córdoba. C.E.C. is a Career Scientist of CONICET, and A.D. is a Fellow of CONICOR.
2 Correspondence: Carlos E. Coronel, Cátedra de Química Biológica, Facultad de Ciencias Médicas, Universidad Nacional de Córdoba, Casilla de Correo 35, Suc. 16, 5016-Córdoba, Argentina. FAX: 54 351 433 3072; ccoronel{at}biomed.uncor.edu
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