Table 4. Expression of a carboxylase mutant with all Cys residues substituted by Ala shows retention of activity that depends on factor IX coexpression.

Baculovirus contents	Carboxylase activity, cpm × 10-3
Single infections
Wild-type carboxylase	238.4
C(all 10)A carboxylase-1	0.2
C(all 10)A carboxylase-2	0.1
Mock	0.0
Factor IX	0.0
Coinfections
Wild-type carboxylase and factor IX	152.4
C(all 10)A carboxylase-1 and factor IX	6.0
C(all 10)A carboxylase-2 and factor IX	6.3

Insect cells were either singly infected with baculovirus-containing carboxylase or factor IX or coinfected with baculoviruses containing both factor IX and carboxylase, and lysates were prepared and assayed for carboxylase activity. All of the permutations shown were tested in a single experiment, and two independently generated C(all 10)A viruses were analyzed. Lysates (100 μl) were assayed in duplicate for 1 h. Background was determined by assaying a sample containing water instead of lysate and gave a value identical to the mock and factor IX samples of the single infections (i.e., ≈500 cpm). The variation in duplicate values was <10%, and the experiment was performed twice.