Characterization of RuBP Carboxylase/Oxygenase of the N. tabacum Mutant Series "Consolation" with Homologous and Non-Homologous Antisera

Abstract

The molar ratio of RuBP carboxylase/oxygenase to the CF1 complex was determined in the wild type N. tabacum var. JWB and in various N. tabacum mutants, which differ with respect to their chloroplast structure and their photosynthetic and photorcspiratory activity. It appears that the ratio RuBP carboxylase oxygenase, CF1 is not constant in the different mutants, and apparently depends on the chloroplast structure and the photosynthetic capacity. In the green phenotypes of N. tabacum var. Consolation, var. NC 95 and var. Xanthi. whose lamellar system consists of a balanced ratio of grana and intcrgrana regions the ratio is 3-4 RuBP car- boxylase/oxygenase molecules per CF1 complex. In chloroplasts of the yellow-green mutant Su/su, and the yellow mutant of N. tabacum var. Consolation, whose lamellar system consists of extended intergrana regions and low stacked grana the RuBP carboxylase oxygcnasc/CF1 ratio is reduced to about one half. The aurea mutant A. tabacum Susu var. aurea and the yel- low-green leaf patches of variegated tabacum var. Xanthi arc characterized by the fact that one molecule RuBP carboxylase oxygenase correlates to two CF1 complexes. Also in the two N. tabacum mutants Su/su and Consolation green, that exhibit a 30% higher photorespiration these molar ratios depend on the chloroplast structure. The determination of the maximal binding of antibodies out of homologous and non-homo- logous antisera onto RuBP carboxylase oxygenase of the N. tabacum mutant Consolation showed, that the enzyme of the green mutant, which exhibits a higher oxygenase activity, has in comparison to the yellow-green and yellow phenotype of this mutant series and also in comparison to the wild type a 30 per cent higher antibody binding capacity. These differences in antibody binding arc shown in both the region of enzyme antibody equivalence and that of antibody excess. With the methods of enzyme-antibody precipitation in agarose gels these differences of enzymes, exhibiting higher or lower oxygenase activities, cannot be detected. The native enzymes and the large subunits of the enzyme of the three Consolation mutants yield in these test reactions with the enzyme of the wild-type fusing precipitation bands. Treatment with the chemical agent hydroxylamine. as well as heat treatment at 50 °C alters the enzyme conformation to such an extent that the antibody binding capacity is increased by 70%. The difference in the higher antibody binding capacity of the enzyme of the green mutant of N. tabacum var. Consolation is maintained also after these chemical modifications.