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Feeding Status Affects In Vivo Prosucrase·Isomaltase Processing in Rat Jejunum^1,2,

USDA/Agricultural Research Service Children's Nutrition Research Center, Department of Pediatrics, Baylor College of Medicine and Texas Children's Hospital, Houston, TX 77030

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 < 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 < 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.

KEY WORDS: • sucrase • isomaltase • processing • jejunum • rats

¹ This project of the USDA/Agricultural Research Service Children's Nutrition Research Center, Department of Pediatrics, Baylor College of Medicine and Texas Children's Hospital, Houston, TX, has been funded in part with federal funds from the USDA/ARS under cooperative agreement number 58-6250-1-003.

² The contents of this publication do not necessarily reflect the views or policies of the U.S. Department of Agriculture, nor does mention of trade names, commercial products or organizations imply endorsement by the U.S. government.

Manuscript received 15 May 1991. Revision accepted 4 October 1991.

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