The activities of nucleoside diphosphate kinase and adenylate kinase are influenced by their interaction

The enzyme nucleoside diphosphate kinase (NDPK) is responsible for maintaining the nucleotide balance in the cell, but is also involved in regulatory functions that often are mediated via protein-protein interactions. Here we present evidence of an interaction between the plant mitochondrial NDPK and a plant mitochondrial adenylate kinase. This is the most highly expressed adenylate kinase gene present in Arabidopsis thaliana. The adenylate kinase cDNA was amplified from A. thaliana and cloned into an expression vector. The recombinant His-tagged protein was produced in Escherichia coli and purified. In vitro experiments using the recombinant enzymes showed that NDPK and adenylate kinase affected the activity of each other. Adenylate kinase stimulated NDPK activity, whereas NDPK inhibited the activity of adenylate kinase, when the total ADP production of the enzymes was measured. The net effect could be an unchanged ADP production, albeit with different rates of substrate consumption. Possible implications in respiration and programmed cell death are discussed.