Practice question

Thermal denaturation affects serum constituents differentially according to thermodynamic stability determined by disulfide content, hydrophobic core packing, and glycosylation. Growth factors platelet-derived growth factor BB homodimer stabilized by two interchain disulfides plus intrachain cysteines, fibroblast growth factor basic bFGF all beta-sheet trefoil without disulfides relatively labile, transforming growth factor beta dimer with nine disulfides but still aggregation prone above fifty degrees, and epidermal growth factor small 6 kDa with three disulfides but beta sheet conformation susceptible to irreversible unfolding above forty five degrees Celsius leading to exposure of hydrophobic patches in core causing aggregation via hydrophobic interactions and loss of receptor binding measured via EGFR phosphorylation western blot reduced eighty percent after sixty degrees ten minutes. Vitamins ascorbic acid vitamin C oxidizes readily at elevated temperature via metal-catalyzed Fenton generating dehydroascorbate further hydrolyzing to diketogulonate and hydrogen peroxide increasing oxidative stress intracellular ROS activating NRF2 stress response altering gene expression, retinol isomerizes. Amino acids glutamine deamidates to glutamate releasing ammonia, tryptophan photo oxidizes forming kynurenine toxic.