pHuman or chicken type III collagen dissolved in 0.1 M-acetic acid was much more potent than type I collagen at inducing platelet aggregation. After incubation in 0.38M-Nasub2/subHPOsub4/sub to promote fibrillogenesis, the platelet-aggregating activity of both collagen types increased, and type I was then virtually equiactive with type III. Preincubation in cell-free plasma increased the activity of chicken but not that of human collagen. The platelet-aggregating activity of type III collagen did not appear to depend on the integrity of the intrachain disulphide bonds./p
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