Sulfite action on ribulosediphosphate carboxylase in the lichen Pseudevernia furfuracea.

Ribulosediphosphate carboxylase can be extracted from Pseudevernia furfuracea, either by Triton X-100 or by pretreatment with liquid nitrogen. With respect to HCO 3(-) the K m is 33 mM. The enzyme is competitively inhibited by sulfite, as is the case with spinach chloroplasts. The K i value (15.5-18.5 mM sulfite) indicates that in lichens the enzyme is not more sensitive than that in spinach. Thus the extreme sensitivity of lichens to SO2 is not based on low tolerance at the enzymatic level, but is due to a low degree of avoidance.