title: Positive cooperativity in substrate binding of human prostatic acid phosphatase entrapped in AOT-isooctane-water reverse micelles.
abstract: The kinetics of 1-naphthyl phosphate and phenyl phosphate hydrolysis, catalyzed by human prostatic acid phosphatase (PAP) entrapped in AOT-isooctane-water reverse micelles, has been studied over surfactant hydration degree (w0) range 5 to 35. Continuous spectrophotometric acid phosphatase assays, previously prepared, were employed. PAP was catalytically active over the whole w0 studied range. In order to determine steady-state reaction constants the experimental data were fitted to Hill rate equation. Positive cooperativity in substrate binding was observed, as it was earlier found in aqueous solutions. The extent of cooperativity (expressed as the value of the Hill cooperation coefficient h) increased from 1 to 4, when the micellar water-pool size was growing, at fixed enzyme concentration. In the plots of catalytic activity (kcat) versus w0, the maxima have been found at w0=10 (pH 5.6) and 23 (pH 3.8). It is suggested that catalytically active monomeric and dimeric PAP forms are entrapped in reverse micelles of w0=10 and 23, respectively.
authors.affiliation: Institute of Medical Biochemistry, Jagiellonian University, Collegium Medicum, Kopernika 7, 31-034 Kraków, Poland. mbwasyle@cyf-kr.edu.pl
authors.forename: Ewa
authors.initials: E
authors.lastname: Luchter-Wasylewska
authors.forename: Małgorzata
authors.initials: M
authors.lastname: Iciek
mesh_terms: D000135:Acid Phosphatase; D006801:Humans; D007700:Kinetics; D008297:Male; D017027:Protein Tyrosine Phosphatases / Q000378:metabolism*; D013379:Substrate Specificity
chemical_list: D000135:Acid Phosphatase; C428439:prostatic acid phosphatase; D017027:Protein Tyrosine Phosphatases