MALTASE-GLUCOAMYLASE: REGULATOR OF STARCH DIGESTION

这个子项目是许多研究子项目中利用 资源由NIH/NCRR资助的中心拨款提供。子项目和 调查员(PI)可能从NIH的另一个来源获得了主要资金， 并因此可以在其他清晰的条目中表示。列出的机构是 该中心不一定是调查人员的机构。 1994年，报告了9例儿童新的糖淀粉酶缺乏和淀粉不耐受综合征。该综合征的特征是慢性腹泻，对从饮食中消除淀粉和淀粉低聚物有反应。所有受试者的空肠葡萄糖淀粉酶活性均较低，组织学检查正常。1998年，我们报道了产生麦芽糖酶(MGA)基因的cDNA序列。1999年，我们在本陶布综合医院发现了一例先天性MGA缺乏症。由于活检葡萄糖水解酶活性与临床症状有很大差异，且MGA主要表达于远端小肠，因此有必要对该患者体内淀粉消化情况进行评估。对淀粉消化的平衡研究是无效的，因为在结肠中存在淀粉消化的挽救途径。利用UL~(13)C-淀粉/未标记葡萄糖低聚物恒速输注6小时，确定UL~(13)C-葡萄糖在血液中的平台状态，建立了一种定量淀粉消化方法。对原始方案的修改包括：不断地将13C-淀粉与多聚糖一起注入；使用UL-13C-淀粉(99%APE)作为MGA底物；以及稳态定量血糖(M+6)同分异构体作为从注入的淀粉中产生的产物，以测量淀粉消化速度。不同的是，剩余的13C-淀粉是提供给结肠进行残存消化的负荷。在这项应用中，我们希望检验这样一种假设，即空肠中的体外糖化酶活性水平可以预测体内的小肠淀粉消化。

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.