MALTASE-GLUCOAMYLASE: REGULATOR OF STARCH DIGESTION

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. In 1994 a new syndrome of glucoamylase deficiency and starch intolerance was reported in nine children. The syndrome was characterized by chronic diarrhea which responded to elimination of starch and starch oligomers from the diet. The subjects all had low levels of jejunal glucoamylase activities and histologically normal biopsies. In 1998, we reported the sequence of the cDNA for the gene that produces maltase-glucoamylase (MGA). In 1999, we discovered a case of congenital MGA deficiency at the Ben Taub General Hospital. Because there are many clinical discrepancies between biopsy glucohydrolase specific activities and clinical symptoms and because of the predominant expression of MGA in distal small bowel, it was necessary to evaluate in vivo digestion of starch in this patient. Balance studies for starch digestion were not effective because of a salvage pathway for starch digestion existing in the colon. A quantitative starch digestion protocol has been developed that uses UL 13C-starch / unlabeled glucose oligomers infused at a constant rate for a period of 6 hours and determines plateau appearance of UL 13C-glucose in blood. Modifications over an original protocol were constant infusion of the 13C-starch with Polycose; and use of UL-13C-starch (99% APE) as MGA substrate; and steady state quantitation of plasma glucose (M+6) isotopomers as products arising from the infused starch to measure rate of starch digestion. By difference, the remaining infused 13C-starch is the load presented to the colon for salvage digestion. In this application we wish to test the hypothesis that level of in vitro glucoamylase activity in the jejunum predicts in vivo small intestinal starch digestion.