Op. Chilson et al., PYRROLINE-5-CARBOXYLATE REDUCTASES IN SOYBEAN NODULES - THE ENZYMES IN HOST CYTOSOL AND BACTEROIDS ARE ANTIGENICALLY DISTINCT, PLANT SCI, 122(1), 1997, pp. 43-50
A previous report showed that cytosolic fractions of both free-living
Bradyrhizobium japonicum and soybean bacteroids exhibited high levels
of pyrroline-5-carboxylate reductase (P5CR) activity and summarized ki
netic evidence for a common reductase which was distinct from that in
nodule host cytosol. In the present study, a polyclonal rabbit antibod
y directed against P5CR in nodule host cytosol (alpha-[P5CR.NHC]) was
prepared. Recognition of the native reductase by alpha-[P5CR.NHC] was
shown by immunoinhibition of the catalytic activity of enzyme from nod
ule host cytosol; the P5CR activities in the cytosolic fractions from
bacteroids and free-living rhizobia were not affected. Immunoblots sho
wed that alpha-[P5CR.NHC] recognized the 30-kDa polypeptide of the pur
ified plant reductase, as well as in nodule host cytosol. A 43-kDa pol
ypeptide was also bound on immunoblots of Bradyrhizobium japonicum cyt
osol, but not of bacteroid cytosol. The 43-kDa species seems not to re
present the rhizobial P5CR, but a cross-reacting antigen of currently
unknown function which is deleted or modified during infection or bact
eroid maturation. Antibody directed against P5CR from Escherichia coli
did not recognize the reductase from nodule host cytosol, either by i
mmunoinhibition or on immunoblots. Copyright (C) 1997 Elsevier Science
Ireland Ltd.