Homotropic allostery of nucleotidase activity of human prostatic acid phosphatase

• Prostatic phosphatase exhibits positive cooperativity towards purine nucleotides.
• Nucleotidase activity of prostatic acid phosphatase exhibits homotropic allostery.

The steady-state kinetics of hydrolysis of four purine ribonucleotides: 3′-AMP, 5′-AMP, 5′-GMP and 5′-IMP catalysed by human prostatic acid phosphatase (PAP; EC 3.1.3.2) in vitro was examined in this study. It has been shown for the first time that nucleotidase activity of PAP exhibits positive cooperativity, or homotropic allostery, in binding the purine ribonucleotides. Therefore, these substrates are homotropic positive effectors, or homotropic allosteric activators, of PAP-catalysed reaction. Enzyme-substrate saturation curves described by Hill equation are sigmoidal and the values of Hill cooperativity coefficient h are higher than 1. The affinity of PAP to substrates, the degree of cooperativity and the efficiency all depend on the chemical nature of the ribonucleotide and they increase in the following order: 5′-AMP < 5′-IMP < 5′-GMP < 3′-AMP, but the enzyme reactivity remains almost equal. Therefore, 3′-AMP is the most efficient PAP substrate while 5′-AMP is the least efficient one of the four ribonucleotides studied. The noncovalent, homoallosteric regulation of the nucleotidase activity of PAP in vitro discovered in this study may be physiologically important in vivo.

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