Heat stress response in pea involves interaction of mitochondrial nucleoside diphosphate kinase with a novel 86-kilodalton protein

In this work we have further characterized the first mitochondrial nucleosi de diphosphate kinase (mtNDPK) isolated from plants. The mitochondrial isof orm was found to be especially abundant in reproductive and young tissues. Expression of the pea (Pisum sativum L. cv Oregon sugarpod) mtNDPK was not affected by different stress conditions. However, the pea mtNDPK was found to interact with a novel 86-kD protein, which is de novo synthesized in pea leaves upon exposure to heat. Thus, we have evidence for the involvement o f mtNDPK in mitochondrial heat response in pea in vivo. Studies on oligomer ization revealed that mtNDPK was found in complexes of various sizes, corre sponding to the sizes of e.g. hexamers, tetramers, and dimers, indicating f lexibility in oligomerization. This flexibility, also found for other NDPK isoforms, has been correlated with the ability of this enzyme to interact w ith other proteins. We believe that the mtNDPK is involved in heat stress r esponse in pea, possibly as a modulator of the 86-kD protein.