Fig. 5. Effect of varying extracellular matrix protein and osteonectin levels on matrix adhesion `activation'. (A) Effect of varying the amount of osteonectin. A constant amount of fibronectin (0.1 µg ml^–1) was coated on the plate together with the indicated amount of osteonectin and attachment was assessed as described in Fig. 1. (B) Effect of varying the amount of matrix protein. A constant amount of osteonectin (4 µg ml^–1) was coated on the plate together with the indicated amounts of extracellular matrix protein and cell adhesion was assessed as described in Fig. 1. Results (mean adhesion ± s.d.) are shown for MDA-231 breast carcinoma cells. Approximately 50% of the total cells adhere to wells coated with 0.2 µg ml^–1 fibronectin + osteonectin representing 2.8 OD. ***P<0.001 and *P<0.05 significant difference between protein alone and protein + OSN was determined by Bonferroni's multiple comparison post-test.