Intracellular location of nitrate reductase and nitrite reductase in spinach and sunflower leaves.

Chloroplasts have been isolated from spinach and from sunflower which retain their outer membrane and their stroma protein as determined both by ability to fix CO2 and evolve O2 at high rates, and by appearance under the phase contrast microscope. Such chloroplasts contain both nitrate and nitrite reductase activity. However, calculations on the distribution of these enzymes, when compared with the distribution of pyruvate kinase and cytochrome c oxidase activity, demonstrate that the larger part of both nitrate and nitrite reductase is located outside of the chloroplast.