FIGURE 7.

Reduced pyridine hemochromogen spectra of metalloporphyrins extracted from various heme-substituted CBS enzymes. Protoporphyrins were released from the respective CBS proteins (200 μg) in 30 mm NaOH and subsequently stabilized by adding 1 volume of pyridine to 3 volumes of the alkali mixture. Samples were reduced with a trace of solid Na₂S₂O₄ and immediately measured. Solid line represents protoporphyrin released from GST-CBS fusion proteins. Dashed line corresponds to relevant protoporhyrin substance used as a standard. Stock solutions of metalloporhyrins were prepared at 2 mg/ml in 0.2 m sodium phosphate, pH 12. The standards were subsequently prepared the same way as the CBS proteins. A, iron; B, manganese; C, cobalt.