Comparison of the structure and function of ribulosebisphosphate carboxylase--oxygenase from a cold-hardy and nonhardy potato species.

A comparison of ribulosebisphosphate carboxylase-oxygenase from the leaves of the nonacclimated, cold-hardy species, Solanum commersonii, and the nonacclimated, nonhardy species, Solanum tuberosum showed that this enzyme from the two species differed in structure and function. The results of sulfhydryl group titration with 5,5'-dithiobis(2-nitrobenzoic acid) indicated that the kinetics of titration and the number of accessible sulfhydryl groups in the native enzymes were different. After 30 min, the enzyme from the hardy species had 1.7 times fewer sulfhydryl groups titrated than that from the nonhardy species. In the presence of 1% (w/v) sodium dodecyl sulfate, the total number of sulfhydryl groups titratable with 5,5'-dithiobis-(2-nitrobenzoic acid) was the same for both species. However, this denaturant had a differential effect on the kinetics of titration with 5,5'-dithiobis(2-nitrobenzoic acid). Both enzymes had a native molecular weight of about 550 000. The quaternary structures of the two enzymes were similar with the presence of large and small subunits of 54 000 and 14 000, respectively. However, there was more polypeptide of 108 000--110 000 present in preparations of the enzyme from S. tuberosum than from S. commersonii. This polypeptide is an apparent dimer of the large subunit on a relative mass basis. The large subunit of the enzyme from S. tuberosum was more sensitive to the absence of reducing agent and was more sensitive to freezing and thawing than the large subunit of the enzyme from S. commersonii. Catalytic properties of both enzymes at 5 and 25 degrees C indicated no significant difference in the Km, CO2 at either temperature. However, the Vmax at 5 degrees C for the enzyme from S. commersonii was 35% higher than that of the enzyme from S. tuberosum. In contrast, the Vmax at 25 degrees C for the enzyme of the hardy species was 250% lower than that of the enzyme from the nonhardy species.