Ribulose Diphosphate Carboxylase from Autotrophic Euglena gracilis

Ribulose 1,5-diphosphate carboxylase (RUDPcase) from autotrophically grown Euglena gracilis was purified to homogeneity as measured by analytical ultracentrifugation, polyacrylamide gel electrophoresis, and immunoprecipitation reactions. The enzyme represented about 9% of total protein and 24% of soluble protein in the autotrophic cell. Light-grown, heterotrophic cells seemed to contain considerably less RUDPcase. Native carboxylase from autotrophic Euglena showed an s_{20, w} at low protein concentrations of 17 to 17.5, suggesting a molecular weight of >500,000 daltons. Upon denaturation, the enzyme dissociated into two subunits having different amino acid compositions and molecular weights of 59,000 and 12,000 daltons. Based upon the amino acid mass ratios, a quaternary organization of 7 to 8 large and 8 to 10 small subunits per native enzyme molecule was indicated.     

Separation of Chlorophyll Degradation from Other Senescence Processes in Leaves of a Mutant Genotype of Meadow Fescue (Festuca pratensis L.)

Chlorophyll levels in l-cm sections of the youngest fully expanded leaves of normal (Y) Festuca pratensis L. declined almost to zero over a period of 6 days after excision. Chlorophyll in a mutant genotype (NY) remained near the initial level for the whole of this period. Abscisic acid promoted pigment loss in Y but had no significant effect on chlorophyll in NY. Kinetin retarded pigment loss in Y but was ineffective in NY. Other biochemical changes associated with leaf senescence—reduction in protein content and the appearance of novel isoenzymes of α-naphthyl acetate esterases—occurred in both genotypes. Abscisic acid accelerated protein breakdown, whereas kinetin inhibited the loss of protein in both genotypes. The mutation thus appears to be expressed as a highly specific lesion in pigment metabolism. We concluded that pigment breakdown, which is widely used as an index of leaf senescence, may not be an inevitable part of the aging process.