Catalase-2, the catalase found in spores of Bacillus subtilis, has been purified to homogeneity from a nonsporulating strain. The apparent native molecular weight is 504,000. The enzyme appears to be composed of six identical protomers with a molecular weight of 81,000 each. The amino acid composition is similar to the composition of other catalases. Like most catalases, catalase-2 exhibits a broad pH optimum from pH 4 to pH 12 and is sensitive to cyanide, azide, thiol reagents, and amino triazole. The apparent Km for H2O2 is 78 mM. The enzyme exhibits extreme stability, losing activity only slowly at 93 degrees C and remaining active in 1% SDS-7 M urea. The green-colored enzyme exhibits a spectrum like heme d with a Soret absorption at 403 nm and a molar absorptivity consistent with one heme per subunit. The heme cannot be extracted with acetone-HCl or ether, suggesting that it is covalently bound to the protein.