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

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 micromol.mg(-1) protein.min(-1)), intermediate in the suckling (9.75 micromol.mg(-l) protein.min(-l)) and the highest in the weaning and post-weaning stage (12.83 and 10.40 micromol.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 micromol.mg protein(-1).min(-1)) and high in the post-weaning stage (13.36 micromol.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 micromol.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.