Alkaline phosphatases (APs) are homodimeric enzymes that catalyze the hydrolysis and transphosphorylation of phosphate monoesters. Alkaline phosphatase activity was determined in different tissue homogenates (flesh and bones) of species four fish species- Coptodon zillii, Heterobranchus bidorsalis, Chrysichthys nigrodigitatus and Clarias gariepinus. The bone was found to have the highest activity of alkaline phosphatase. The Km and Vmax values for the fish bone alkaline phosphatase (FBAP) were estimated to be 0.0106mM and 2.1730 µmol/min/mol for C. zillii, 0.0074mM and 3.1868 µmol/min/mol for H. bidorsalis, 0.0226mM and 8.9928 µmol/min/mol for C. gariepinus and 0.0104mM and 6.0753 µmol/min/mol for C. nigrodigitatus respectively. The pH optimum of the enzyme for the categories of fishes was estimated to be 9.0. Divalent metals such as Mg2+ and Ca2+ enhanced enzyme activity but have an inhibitory effect at concentration above 1.5 mM. The highest activity of the enzyme in the bone of the four species of fishes in this study suggests that most of the organic phosphates in the species are hydrolysed principally in this tissue. This enzyme also plays the role of metabolic regulations.
Keywords: characterization, alkaline phosphatase, homogenates, freshwater fish.