Purification and properties of the heat-released nucleotide-modifying group from the inactive iron protein of nitrogenase from Rhodospirillum rubrum

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Abstract
Nitrogenase in R. rubrum is regulated in vivo by the covalent modification of the Fe protein. This paper reports the isolation, purification and properties of the modifying group that were heat released from the Fe protein. The molecule is isolated from the heated mixture by binding to a boronate affinity column. Purification is achieved on an ion-exchange high-performance liquid chromatography column. Structural properties of the molecule were investigated by using proton and P NMR, mass spectrometry, enzyme susceptibility and chromatographic methods. The heat-released modifying group exhibits an unusual signal in the proton NMR spectrum at 1.26 ppm. The molecule also contains a functional group which can be reduced by borohydride. This group is lost on breakdown of the molecule or upon treatment of the molecule with 5''-nucleotidase. The identity of the base and the pentose of modifying group as adenine and ribose, respectively, is confirmed. Ratios of the known components of the modifying group are established.