Novel secreted maltase activity enables suckling mouse pup starch digestion

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Starch requires 6 enzymes for digestion to free glucose: 2 amylases (salivary and pancreatic) and 4 mucosal maltase activities; Sucrase‐isomaltase (Si) and Maltase‐glucoamylase complexes (Mgam). All 6 activities are deficient in suckling rodents.Objective: Test 13C‐starch digestion before weaning (at 21d) from mother's milk by measuring enrichment of blood 13C‐glucose in Mgam Null and Wild Type mice.MethodsMgam gene was ablated at the N‐terminal expressing the membrane binding domain. Dams were fed low 13C‐diet and litters kept on low 13C‐diet. Pups were weaned at 21d. Digestion was tested at 13d and 25d by intragastric feeding of amylase predigested UL 13C‐α‐limit dextrins (LDx). Blood 13C‐glucose enrichment was measured by GCRMS using pentaacetate derivatives.Results4 h after feeding, blood 13C‐glucose MPE% was enriched by 26×103 in null and 18×103 foldat 13d and 0.3×103 and 0.2×103 fold at 25d (vs. fasting p = 0.045 and p = 0.045). By jejunal enzyme assay, imunohistochemistry or Western blots there was no maltase activity or brush border staining with anti‐Si or Mgam antibodies at 13d but these were fully developed in WT by 25d. In 13d null mice lumenal contents were stained by both specific antibodies.Conclusion1. 13C‐LDx was rapidly digested to 13C‐glucose in 13d mice independent of age, Mgam genotype or mucosal maltase activity. 2. This novel observation demonstrates that a maltase activity is secreted which enables suckling pup starch digestion well before brush border enzyme development. 3. The origin of this secreted starch digesting activity is presently uncertain.