Methylene blue sensitized photo-oxidation of collagen fibrils

Isometric tension measurements on rat tail tendons showed that visible light in the presence of Methylene blue led to an increase in the thermal stability of the collagen. Analysis of CNBr fragments by SDS-polyacrylamide gel electrophoresis showed a decrease in the amounts of low molecular weight fragments and an increase in the formation higher molecular components with irradiation time. Amino-acid analysis data indicated that the relative yields of only tyrosine, methionine and histidine were reduced by the irradiation, with the loss of histidine being the greatest. The loss of methionine was not sufficient to completely account for the increases in the CNBr fragment sizes. Comparable results were also obtained with ultra-violet light. These thermal and chemical data were interpreted as being due to the formation of new intermolecular cross-links in the tendon collagen. X-ray fibre diffraction showed that the irradiation and the induced cross-linking did not lead to a substantial change or disorder in the molecular packing arrangement within the native collagen fibril.