[Form of the tropocollagen macromolecule]

It has been shown with electron microscope that the form of the tropocollagen macro-molecule in solution is determined by hydrogen ions concentration. It is proposed that in native collagen fibrils the tropocollagen macromolecules have an unknown before form of rods with the thickened central part. Their length is about 1000 A. The known extended form of the tropocollagen macromolecule (the rod of 2800 A length) is probably transformed to the described form by the folding of the macromolecule. The origin of cross striation of the collagen fibril is discussed.