Figure 3.

(A) Thermal denaturation of yeast protoporphyrinogen oxidase measured by CD. The purified native enzyme (10 μM) used either was the untreated native enzyme (−HA) or had been treated with hydroxylamine (+HA). Temperature increases of 60°C⋅h⁻¹ were used, and the CD was measured at 222 nm. (Lower) The table summarizes the T_m values of the enzyme on sample protein after (+) or without (−) prior treatment with hydroxylamine or PMSF and measured in the absence (−) or presence (+) of 100 μM acifluorfen. (B) First derivative of the melting curves shown in A, measured on a freshly prepared enzyme (Upper) or on an enzyme preparation stored for 3 mo at −20°C (Lower). (C) Solvent denaturation of yeast protoporphyrinogen oxidase measured by CD. The purified native enzyme (10 μM) used either was the untreated native enzyme (−HA) or had been treated with hydroxylamine (+HA). The CD was measured at 222 nm as a function of urea concentration.