CHAPERONIN-REPAIRABLE SUBTLE INCOMPLETENESS OF PROTEIN ASSEMBLY INDUCED BY A SUBSTITUTION OF HYDROGEN WITH DEUTERIUM - EFFECT OF GROE ON DEUTERATED RIBULOSE 1,5-BISPHOSPHATE CARBOXYLASE

For investigating the effect of slight modification of proteins on the ir higher-ordered structure, and that of chaperonin on the functional assembly of proteins, we prepared partially deuterated ribulose 1,5-bi sphosphate carboxylase (Rubisco) by cultivating Chlorella ellipsoidea in 100 mol% D2O medium. Chlorella cells grown in the D2O medium (D-Chl orella) contained almost the same amount of Rubisco (D-Rubisco) as the cells grown in H2O medium (H-Chlorella) determined by Western blottin g using Rubisco-specific antibody, whereas the activity of D-Rubisco d etermined by carbon fixation was only 28% of that of Rubisco from H-Ch lorella (H-Rubisco). D-Rubisco, however, showed similar K-m and pH and temperature optima to those of H-Rubisco as well as similar antibody binding capability. The enzyme activity of D-Rubisco was recovered to 84% of that of H-Rubisco by the addition of GroE proteins (GroEL, chap eronin 60, and GroES, chaperonin 10), members of the chaperonin family produced by Escherichia coil. These data suggest that D-Rubisco has s ubtle incompleteness in terms of functional assembly, a situation that is correctable by chaperonin.