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Developmental and dietary induction of the 90K subunit of rat intestinal phytase
Insights
Weaning significantly impacts rat intestinal phytase activity and subunit composition. Phytic acid in the diet accelerates the induction of the 90K subunit, enhancing enzyme efficiency.
Area of Science:
- Biochemistry
- Developmental Biology
- Animal Nutrition
Background:
- Intestinal phytase and alkaline phosphatase activities increase during rat development.
- Phytase enzyme subunits (70K and 90K) show differential expression patterns.
- The 90K subunit appears around the weaning period.
Purpose of the Study:
- To investigate the role of weaning and dietary factors in phytase subunit composition changes.
- To understand the developmental regulation of phytase activity and subunit expression.
- To elucidate the functional significance of the 90K subunit in phytase activity.
Main Methods:
- Comparative analysis of phytase activity and subunit expression in rats at different developmental stages.
- Dietary manipulation studies (casein, casein with phytate) in weanling rats.
- Enzyme kinetic analysis (Km values for phytate and p-nitrophenyl phosphate).
- pH-dependence studies of phytase activity.
Main Results:
- Forced weaning accelerated 90K subunit appearance and enzyme activity.
- Casein diet delayed induction, while phytate supplementation accelerated it.
- The Km for phytate significantly decreased from suckling to adult rats.
- The 90K subunit's presence correlated with efficient phytase activity and altered substrate affinity.
Conclusions:
- Weaning is a critical factor influencing phytase subunit composition and activity.
- Dietary phytic acid intake accelerates the induction of the 90K subunit.
- The 90K subunit is crucial for efficient phytase activity, particularly for phytate hydrolysis.
Abstract:
The activities of phytase and alkaline phosphatase in the intestine gradually increased in parallel during development of rats, but the 70K and 90K subunits were expressed differentially; only the 70K subunit was detected at birth, whereas the 90K subunit appeared at the weaning period (3 weeks after birth). When rats were forced to wean at 18 days old and fed laboratory chow, the enzyme activity increased markedly and the 90K subunit appeared within 1 day. These findings suggest that weaning is involved in the change in the subunit composition. Increases in the enzyme activity and amount of the 90K subunit were significantly delayed by feeding weanling animals on casein diet, but induced significantly by feeding them on casein diet supplemented with phytate. Thus induction of the 90K subunit seems to be accelerated by intake of phytic acid in the diet. The Km value of the enzyme from suckling rats for phytate was 5.25 mM, while that of adult rats was 0.213 mM. In contrast, the Km value for p-nitrophenyl phosphate (PNPP) was constant during development. The phytase activity of suckling rats did not show a distinct pH-dependence. These findings suggest that the 90K subunit may play some important roles in expressing an efficient phytase activity.