Feeding status affects in vivo prosucrase.isomaltase processing in rat jejunum.
Fed and fasted (18 h) adult male rats received a primed constant infusion of [3H]leucine for 15 to 180 min. Prosucrase-isomaltase (pro-SI) and sucrase were isolated from mixed jejunal mucosal membranes by immunoprecipitation and separated from one another by polyacrylamide gel electrophoresis under denaturing and reducing conditions. The rate at which pro-SI was processed to sucrase was calculated on the assumption that the steady-state specific radioactivity of leucine in pro-SI defined the pool of amino acids used in the formation of brush border sucrase. At isotopic steady state, pro-SI achieved a specific radioactivity that was higher than that of mucosal free leucine in both feeding groups. The relationship between the isotopic equilibrium of the free amino acid pools and pro-SI was sensitive to feeding status; the specific radioactivity of pro-SI was 25 and 55% (P less than 0.05) of the blood specific radioactivity in fed and fasted animals, respectively. The fractional rate of pro-SI processing tended to be higher (P less than 0.07) in fed (407%/d) than in fasted animals (274%/d). We conclude that the general mucosal free amino acid pool is not the amino acid pool from which pro-SI is synthesized and that the rate of pro-SI processing from the endoplasmic reticulum-Golgi membranes to the brush border membrane is sensitive to the feeding status of the animal.
Dudley
M A
MA
Department of Pediatrics, Baylor College of Medicine, Houston, TX.
Nichols
B L
BL
Rosenberger
J
J
Perkinson
J S
JS
Reeds
P J
PJ
D000596:Amino Acids / Q000032:analysis / Q000097:blood; D000818:Animals; D003720:Densitometry; D004591:Electrophoresis, Polyacrylamide Gel; D004792:Enzyme Precursors / Q000302:isolation & purification / Q000378:metabolism*; D007413:Intestinal Mucosa / Q000737:chemistry; D007583:Jejunum / Q000201:enzymology*; D008297:Male; D008871:Microvilli / Q000201:enzymology; D009834:Oligo-1,6-Glucosidase / Q000302:isolation & purification / Q000378:metabolism*; D011233:Precipitin Tests; D051381:Rats; D013393:Sucrase / Q000302:isolation & purification / Q000378:metabolism*
D000596:Amino Acids; D004792:Enzyme Precursors; D009834:Oligo-1,6-Glucosidase; D013393:Sucrase