AJP - Gastrointestinal and Liver Physiology, Vol 251, Issue 6 736-G743, Copyright © 1986 by American Physiological Society
Alteration of intracellular synthesis of surface membrane glycoproteins in small intestine of iron-deficient rats
J. P. Buts, J. Vamecq and F. van Hoof
We studied the activity and kinetic parameters of microvillous enzymes in
intestinal villous cells and the concentration of the secretory component
(SC) of p-immunoglobulin A in subcellular fractions of crypt cells in
35-day-old rats made iron deficient from birth and in controls. The aim of
the study is to investigate the biochemical basis for the decreased
activity of brush-border disaccharidases observed in growing animals with
chronic iron deficiency. In rats made iron deficient, the specific (per
unit protein) and the total (per total intestinal length) activities of
sucrase, lactase, maltase, aminopeptidase, and diamine oxidase were
decreased from -17 to -66% compared with the activities measured in the
controls. The lower activity of sucrase in the brush-border membrane of the
iron-deficient rats was associated with much slower enzyme synthesis rate
than in control animals. Km of sucrase was identical in both iron-deficient
rats and controls, but the maximum velocity of enzyme reaction was reduced
proportionally to the enzymatic activity, indicating a lesser amount of
enzyme rather than an inactivation. Electron microscopy of epithelial
villous cells from iron-deficient rats revealed a marked rarefaction of
secretory granules (transport vesicles) without apparent change in the
morphology of the brush-border membrane or of cellular organelles. In
villus and crypt cells isolated from the jejunum of iron-deficient rats, SC
concentration was reduced to a level about half that of the controls. When
SC concentration was measured in subcellular fractions of crypt cells, SC
content in each fraction was two to three times lower in iron-deprived rats
than in controls without evidence of accumulation of the protein at a given
subcellular level.(ABSTRACT TRUNCATED AT 250 WORDS)
