14‐3‐3 proteins control proteolysis of nitrate reductase in spinach leaves

Abstract
To test a possible role of 14‐3‐3 proteins in the degradation of nitrate reductase (NR) in leaves, we monitored 14‐3‐3s bound to NR in leaf extracts. The amount of 14‐3‐3s that coimmunoprecipitated with serine 543 phospo‐NR (p‐NR) increased upon a light/dark transition. This was accompanied by a similar increase in the protein turnover rate of NR in leaves. Purified NR was degraded in extracts from darkened but not from illuminated leaves. Removal of 14‐3‐3s from such extracts prevented NR degradation. We conclude that the availability of 14‐3‐3s for p‐NR regulates the stability of NR.