The inhibitor protein of phosphorylated nitrate reductase from spinach (Spinacia oleracea) leaves is a 14‐3‐3 protein

The inhibitor protein (IP) that inactivates spinach leaf NADH:nitrate reductase (NR) has been identified for the first time as a member of the eukaryotic 14‐3‐3 protein family based on three lines of evidence. First, the sequence of an eight amino acid tryptic peptide, obtained from immunopurified IP, matched that of a highly conserved region of the 14‐3‐3 proteins. Second, an authentic member of the 14‐3‐3 family, recombinant Arabidopsis GF14ω, caused inactivation of phospho‐NR in a magnesium‐dependent manner identical to IP. Third, an anti‐GF14 monoclonal antibody cross‐reacted with IP and anti‐IP monoclonal antibodies cross‐reacted with GF14ω.

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