In vivo sucrase-isomaltase and lactase-phlorizin hydrolase turnover in the fed adult rat.

Dudley MA, Hachey DL, Quaroni A, Hutchens TW, Nichols BL, Rosenberger J, Perkinson JS, Cook G, Reeds PJ
J Biol Chem. 1993 268 (18): 13609-16

PMID: 8514793

We estimated in vivo turnover rates of sucrase-isomaltase and lactase-phlorizin hydrolase in adult rats. Fed animals received a primed continuous infusion of phenylalanine (300 microCi, 150 mumol Phe/100 g of body weight for 30 s, then 7.5 microCi, 3.75 mumol Phe/min for 10 to 140 min). Sucrase-isomaltase and lactase-phlorizin hydrolase were immunoprecipitated from jejunal mucosal membranes; isoforms were separated by SDS-polyacrylamide gel electrophoresis. Endoglycosidase H digestions and (for lactase-phlorizin hydrolase) N-terminal amino acid sequencing were performed on all isoforms. Specific radioactivity of prosucrase-isomaltase and prolactase-phlorizin hydrolase isoforms reached isotopic equilibrium by 60 and 90 min, respectively. Specific radioactivity of brush border sucrase and lactase did not reach steady state. The isotope kinetic, N-terminal amino acid sequencing, and endoglycosidase H digestion data suggested that one of the high molecular weight lactase isoforms is a dimer of mature lactase. Compartmental modeling of specific radioactivity demonstrated that mean intracellular residence time is 59 min for prosucrase-isomaltase isoforms and 68 min for prolactase-phlorizin hydrolase isoforms. Mean residence time in the brush border was 5.8 h for sucrase and 7.8 h for lactase. Fractional synthesis rates were 414%/day for sucrase and 307%/day for lactase. Thus, in vivo brush border sucrase and lactase turn over at similar rates in the adult rat.

MeSH Terms (14)

Amino Acids Amino Acid Sequence Animals Food Intestinal Mucosa Isoenzymes Lactase-Phlorizin Hydrolase Male Microvilli Molecular Sequence Data Phenylalanine Rats Rats, Sprague-Dawley Sucrase-Isomaltase Complex

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