Table 2.

Hemin and protoporphyrin IX binding constants for SpyB protein variants.

Protein	Hemin, KD (M)	Protoporphyrin IX, KD (M)
SpyB	2.6 × 10−6 ± 0.6 × 10−6	4.9 × 10−6 ± 0.8 × 10−6
MBP-SpyB	1.2 × 10−5 ± 0.4 × 10−5	NDa
MBP-SpyB C7A/C13A mutant	3.7 × 10−5 ± 1.2 × 10−5	ND
MBP-SpyB C7A/C13A/C30A/C35A mutant	3.2 × 10−4 ± 2.1 × 10−4	ND

^aNot determined.