Table 1.

Binding of ³⁵S-labeled gelatinase A

Experiment	Form of Gel A	Substrate	Radioactivity bound, %
1	Proenzyme	Fibroblast monolayer	4
	Proenzyme	24-h lattice	3.8
2	Proenzyme	Cell-free collagen gel	9
	Active enzyme	Cell-free collagen gel	10

In experiment 1, ≈50,000–70,000 cpm (0.5–1 μg) of ³⁵S-labeled gelatinase A was added to equal numbers of cells in monolayer or in lattice culture. After 24 h, the monolayer and contracted lattice were washed extensively, and the cells were extracted with lysis buffer. Supernatants, washes, and extracts were all counted separately in a scintillation counter. The percentage of radioactivity bound represents the remaining counts after six washes and extraction. In experiment 2, the labeled enzyme was incorporated into cell-free collagen lattices and incubated for 2 h at 37°C. Medium was removed, and the lattices were washed three to five times with cold PBS. Medium, washes, and lattice were counted separately. Counts bound remained with the lattice pellet. Gel A, gelatinase A.