Structural characterization and hypoglycemic activity of glycoproteins extracted from Porphyra haitanensis by ammonium sulfate and ethanol extraction methods

In this study, two glycoproteins were extracted from porphyra haitanensis by ammonium sulfate and ethanol extraction methods, and their differences in structure and hypoglycemic activity were compared. The results showed that the protein, amino acid, and galactose contents of the glycoprotein (PG) extracted using an ammonium sulfate method were higher than those of glycoprotein (PP) extracted from ethanol. PG inhibited both α-amylase and α-glucosidase, substantially reduced in vivo hyperglycemia, regulated the intestinal production of beneficial bacteria (Lachnospiraceae, Odoribacter, and Lactobacillus), and increased the abundance of commensal microbial metabolites (e.g., taurine and hypotaurine) via the activation of taurine and hypotaurine, butanoate metabolism, and insulin secretion pathways. PP was superior in regulating lipid metabolism through the AMPK and fatty acid degradation pathways, which was positively correlated with its increased polysaccharide fragment, Lactobacillus and Rikenellaceae_RC9_ gut_group. Our findings shed light on the potential of Porphyra haitanensis glycoproteins as novel natural antidiabetic compounds.