Molecular Weight and Quaternary Structure of Yeast L-Lactase Dehydrogenase (Cytochrome b2).

1. A new determination of the extinction coefficient of the Soret band of reduced cytochrome b2 provides a value of 183 mM-1cm-1 instead of the generally accepted figure of 232. Four methods were used: pyridine hemochromogen, dicyanide complex, spectrum in formic acid and iron titration. No significant differences are observed in the heme spectral properties of cytochrome b2 and its low molecular weight derivative "cytochrome b2 core". 2. Dry weight associated with iron and heme content determinations lead to a minimal molecular weight per heme of 58 600. This result combined with hydrodynamic and crystallographic studies by other authors allows one to propose a tetrameric structure for cytochrome b2. [ABSTRACT FROM AUTHOR]