The Contribution of Different Subunits of Intestinal Mucosal α-glucosidases to the Glucose Release from Starches (P08-090-19)

Abstract

ObjectivesTo analyze the role of each subunit from Sucrase-Isomaltase (SI) and Maltase-Glucoamylase (MG) on the glucose production from corn starch (NC), Waxy starch (WX) and Hylon V (HLV) starch predigested with pancreatic amylase (Amy). MethodsThe starches were selected based on their ratios of α-1,4 and α-1,6 linkages. Starches were predigested with Amy for 0, 10, 20, 30, 60 and 120 min. After predigestion starches were hydrolyzed with different combinations of recombinant C terminal (C) and N terminal (N) subunits of Sucrase-Isomaltase (SI) and Maltase-Glucoamylase (MG), each at the relative maltase activity of: 40% C-SI, 20% N-SI, 32% C-MG and 8% N-MG, resembling the observed in the human intestinal mucosa. Glucose release was quantified by a real-time glucose oxidase-peroxidase method at 37°C. ResultsC-MG subunit hydrolyzed the three starches without predigestion by Amy at rates of 2.9 ± 0.02, 2.5 ± 0.02 and 2.4 ± 0.05 ng/min of glucose for WX, HLV and NC, respectively. C-SI subunit produced only 0.9 ± 0.02 ng/min glucose from the starches not predigested by Amy. After 30 min of Amy predigestion, the rates of glucose release by C-MG were modified to 13.3 ± 0.09, 12.3 ± 0.08 and 11.6 ± 0.08 ng/min for HLV, NC and WX, respectively. The same predigestion modified glucose release by C-SI subunit to 3.9 ± 0.02, 4.7 ± 0.08 and 5.8 ± 0.03 for WX, NC and HLV, respectively. In starches predigested 60 or 120 min, C-MG subunit alone or together with N-MG showed lower activity than expected, suggesting the occurrence of substrate inhibition. Together the four MG and SI subunits showed clear differences on the rates of glucose production from the starches predigested with Amy for 120 min (22.8 ± 0.133 for WX, 26.4 ± 0.2 for NC and 26.7 ± 0.8 for HLV; all ng/min) which correlated with the glucose production by the N and C SI subunits together (15.5 ± 0.9 for WX, 19.4 ± 0.09 for NC and 23.85 ± 0.12 for HLV; all ng/min). ConclusionsWe found complex interactions among the starch structure, extent of amylase digestion and the rate of glucose release by each C and N subunits of SI and MG. Thus, the rate of intestinal starch digestion depends on the structure of the starches, the predigestion by amylase and, importantly, the relative abundance and catalytic properties of the individual subunits of MG and SI. Funding SourcesConsejo Nacional de Ciencias y Tecnología (CONACyT), Mexico.