Non-enzymic interactions of carbohydrates and proteins are a major feature of cumulative modification in basement membranes in the course of diabetic microvascular complications. To evaluate the significance of both glycation and glycoxidation reactions for subsequent alterations of biochemical properties, we examined the effects of in vitro glycation on distinct collagen IV domains under different experimental conditions. The 7 S domain and the major triple-helical domain from human placental collagen IV were incubated for various time intervals up to 14 days at 37 degrees C in the presence of different concentrations of either glucose or ribose under oxidative and antioxidative conditions. Carbohydrate-induced non-enzymic modification in two collagen IV domains was revealed by increased cross-linking and fluorescence. In addition, these non-enzymic modifications apparently have a major impact on molecular conformation and thermal stability of collagen IV, which in turn might influence both cell-matrix interactions and matrix assembly.