X-band EPR spectra of SP lyase. Spectra of the as-isolated enzyme (A), enzyme photoreduced with 5-deazariboflavin (B), and photoreduced enzyme to which S-adenosyl-L-methionine (AdoMet) has been added (C) are presented. The protein was in 20 mM sodium phosphate, 350 mM NaCl, 5% glycerol, pH 7.5. The as-isolated protein was 640 μM; the reduced sample was 600 μM and was prepared with the addition of 5 mM DTT and 100 μM 5-deazariboflavin. The reduced plus AdoMet sample was 560 μM and was prepared by adding AdoMet to 3 mM final concentration after reduction with 5-deazariboflavin. Conditions of measurement: temperature 12 K; microwave power 2 mW; microwave frequency 9.24 GHz; modulation amplitude 10.00; receiver gain 1.6 × 103. The average of two scans is presented. SPL SP lyase