Postnatal ontogeny of kinetics of porcine jejunal brush border membrane-bound alkaline phosphatase, aminopeptidase N and sucrase activities

Abstract

Our objectives were to determine postnatal changes in the maximal enzyme activity ( V max) and enzyme affinity ( K m ) of jejunal mucosal membrane-bound alkaline phosphatase, aminopeptidase N and sucrase using a porcine model which may more closely resemble the human intestine. Jejunal brush border membrane was prepared by Mg 2+-precipitation and differential centrifugation from pigs of suckling (8 days), weaning (28 days), post-weaning (35 days) and adult (70 days) stages. p-Nitrophenyl phosphate (0–8 mM), l-alanine- p-nitroanilide hydrochloride (0–28 mM) and sucrose (0–100 mM) were used in alkaline phosphatase, aminopeptidase N and sucrase kinetic measurements. V max of alkaline phosphatase was the lowest in the adult (4.27 μmol·mg −1 protein·min −1), intermediate in the suckling (9.75 μmol·mg −l protein·min −l) and the highest in the weaning and post-weaning stage (12.83 and 10.40 μmol·mg −l protein·min −l). K m of alkaline phosphatase was high in the suckling and weaning stages (5.14 and 9.93 mM) and low in the adult (0.66 mM). V max of aminopeptidase N was low in the suckling (7.04 μmol·mg protein −1·min −1) and high in the post-weaning stage (13.36 μmol·mg −l protein·min −l). K m of aminopeptidase N was the highest in the two weaning stages (2.96 and 3.39 mM), intermediate in the adult (2.33 mM) and the lowest in the suckling stage (1.66 mM). V max of sucrase increased from the suckling to the adult (0.48–1.30 μmol·mg −l protein·min −l). K m of sucrase ranged from 11.19 to 16.57 mM. There are dramatic postnatal developmental changes in both the maximal enzyme activity and enzyme affinity of jejunal brush border membrane-bound alkaline phosphatase, aminopeptidase N and sucrase in the pig.