AJP - Gastrointestinal and Liver Physiology, Vol 239, Issue 6 524-G531, Copyright © 1980 by American Physiological Society
Turnover of intestinal brush-border proteins during postnatal development in rat
B. Seetharam, K. Y. Yeh and D. H. Alpers
Protein turnover in brush-border membranes of rats during postnatal
development has been studied by the double isotope technique. Unlike adult
animals where only large proteins (mol wt > 140,000) show relatively
rapid turnover, most brush-border proteins in 12-day-old rats show high
3H-to-14C ratios of leucine incorporation, consistent with rapid turnover.
Lysosomal proteases, including cathepsin B, are partly responsible for this
rapid turnover. This conclusion is based on the following findings: 1) In
vivo treatment of 12-day-old animals with leupeptin, an inhibitor of
cathepsin B, alters relative turnover rates, enzyme activity, and content
of many brush-border proteins. Activities of maltase and trehalase rise
while lactase falls. 2) Cathepsin B activity falls rapidly in intestine
after the animals are 16 days of age, at a time when luminal pancreatic
proteases are rising. Moreover, cathepsin B activity shows less latency in
distal intestine at 12 and 16 days than at later ages or in proximal
intestine. It is suggested that during postnatal development lysosomal
enzymes, e.g., cathepsin B, play an important role in the turnover of
intestinal brush-border proteins.
