INVESTIGATION OF THE SITE OF SYNTHESIS OF CHLOROPLASTIC ENZYMES OF NITROGEN-METABOLISM BY THE USE OF HEAT-TREATED 70S RIBOSOME-DEFICIENT RYE LEAVES

The activities of the enzymes nitrate reductase (EC 1.6.6.1), nitrite reductase (EC 1.6.6.4), glutamine synthetase (EC 6.3.1.2), glutamate synthase (GOGAT; EC 1.4.7.1), glutamate-oxaloacetate aminotransferase (EC 2.6.1.1), and glutamate dehydrogenase (EC 1.4.1.2) were compared in light-grown green or etiolated leaves of rye seedlings (Secale cereale L. cv. Halo) raised at 22.degree. C, and in the bleached 70S ribosome-deficient leaves of rye seedlings grown at a non-permissive high temperature of 32.degree. C. Under normal permissive growth conditions the activities of most of the enzymes were higher in light-grown, than in dark-grown, leaves. All enzyme activities assayed were also observed in the heat-treated 70S ribosome-deficient leaves. Glutamine synthetase, glutamate synthase, and glutamate-oxaloacetate aminotransferase occurred in purified ribosome-deficient plastids separated on sucrose gradients. For glutamate-oxaloacetate aminotransferase four multiple forms were separated by polyacrylamide gel electrophoresis from leaf extracts. The chloroplastic form of this enzyme was also present in 70S ribosome-deficient leaves. It is concluded that the chloroplast-localized enzymes nitrite reductase, glutamine synthetase, glutamate synthase and glutamate-oxaloacetate aminotransferase, or their chloroplast-specific isoenzyme forms, are synthesized on cytoplasmic 80S ribosomes.