Immunodetection of ribulose-1,5-bisphosphate carboxylase in mutants of Euglena gracilis impaired in photosynthesis

For the first time, an antibody is used to detect the presence and to measure the concentration of ribulose-1,5-biphosphate carboxylase (RuBPCase) in several mutants of Euglena gracilis impaired in photosynthesis. Where present, the enzyme is correlated to its activity and to the chlorophyll content and photosynthetic CO₂-fixation ability of the respective mutants. Dark-grown wild-type strains Z and bacillaris and mutants O₁BS, O₂BX, G₁BU and P₁BXL (which make normal sized chloroplasts with abnormal internal structure in the light) and Y₁BXD (which does not develop the plastid beyond the proplastid stage in the light) each has about 0.1 × 10^-11 μmol of active RuBPCase/cell. RuBPCase content increases in the light, but to a greater extent oin wild-type cells than in the above mutants, except possibly for mutant G₁BU. The specific activity of the RuBPCase in vivo is estimated from the data to be about 1 nmol CO₂-fixed min^-1 (pmol RuBPCase)^-1 in the light for both the wild-type and the above mutant strains and in the dark for the wild-type Z and some of the above mutant strains. RuBPCase was not detected in mutants Y₃BUD, W₃₄ZUD, SM-L1, W₃₇HeHL and W₃BUL, but was detected in mutant Y₉ZNa1L which has no detectable protochlorophyll(ide) or chlorophyll(ide). In addition to recognizing both the large and small subunits of RuBPCase, the antibody also recognizes a polypeptide of > 60 000 daltons whose function is unknown.