The action of semicarbazide on the aggregation of the tropocollagen macromolecule.

1. A difference in conformation was found between the collagen in solutions treated with semicarbazide hydrochloride and those treated with sodium chloride. This difference could be correlated with the difference in extent of aggregation between the fibrils precipitated from these solutions. 2. The action of semicarbazide hydrochloride depended on the pH and temperature of treatment in a complex manner. At constant temperature semicarbazide enhanced aggregation at pH values less than 4.3, but decreased aggregation was observed at pH values greater than 5.0. At pH 4.3 the effect of semicarbazide on aggregation varied with temperature, the tendency to increased aggregation being more pronounced at 34 degrees and 36-37 degrees . Similar increased aggregation tendencies superimposed on an overall decreased aggregation were observed at these temperatures at pH8.9. 3. A specific binding of semicarbazide to the collagen molecule was indicated.