|Nichols, Buford -|
|Quezada-Calvillo, Roberto -|
|Ao, Zihua -|
Submitted to: Journal of Federation of American Societies for Experimental Biology
Publication Type: Abstract Only
Publication Acceptance Date: April 22, 2009
Publication Date: April 22, 2009
Citation: Nichols, B.L., Quezada-Calvillo, R., Ao, Z. 2009. Slow starch digestion redefined at limit dextrin level by mucosal maltase-glucoamylase and sucrase-isomaltase activities [abstract]. Journal of Federation of American Societies for Experimental Biology. 23:351.2. Technical Abstract: Mucosal maltase-glucoamylase (MGAM) and sucrase-isomaltase (SI) digest free glucose from food starches. Amylase (AMY) amplifies these mucosal activities by production of soluble limit dextrins (LDx). This network of enzyme activities determines rate of LDx entry into either the glycemic or the fermentive pathways. We determined the roles of the mucosal activities as a function of AMY treatment and LDx substrate. Recombinant human AMY was used to produce 8 different LDx. Steady state (SS) was reached after 30 min of AMY treatment. These substrates were incubated with human jejunal lysates (LYS) or immunopurified (IP) MGAM or SI. Glucogenesis was measured by real-time assay. Rates were normalized to maltose. Normal maize with MGAM-IP was used as reference for calculations of % slowly digesting LDx (% RLDx) at SS. LYS SS-rates for other LDx were less than normal maize. SS-rate was always fastest with MGAM-IP but all rates varied by LDx substrate. LYS activity rate was amplified by AMY ~12 X. AMY amplified SI-IP more than MGAM-IP. LYS SS-assays revealed 20% RLDx for normal maize; 30% for potato; 33% for tapioca; 36% for Ae, sugary2 and waxy maize; 40% for rice; and 60% for glycogen. LYS rate best correlated with SI-IP rate (R2 = 93). The MGAM-IP and SI-IP activities of jejunal LYS digested the 8 LDx to glucose with only 60-80% efficiency. The % RLDx entering the fermentive pathway was underestimated by previous assays with fungal enzymes.