Regulation of peanut glutamate dehydrogenase by methionine sulphoximine
Peanut glutamate dehydrogenase (GDH) was electrophoretically purified to homogeneity. Rotofor IEF fractionated the peanut GDH to 7 isoelectric (charge) isomers, which focused in the pH 5-8 range. Western blot analysis of the charge isomers using anti-GDH serum showed that methionine sulphoximine (MSX) treatment suppressed the b-subunit (69 KDa), but enhanced the a- subunit (45 KDa), and α-subunit (46 KDa) of the enzyme. The MSX-mediated suppression of the b-subunit increased the NH4/+ K(m) value of the acidic charge isomers from 77 mM in the control to 50 mM in the MSX-treated peanut, and also increased the 2-ketoglutarate K(m) value of the basic charge isomers from 0.4 mM in the control to 7.0 mM in the MSX treatment. Therefore, the control peanut could salvage NH4/+ with its GDH activity. But by increasing the NH4/+ K(m) value, the MSX rendered the enzyme ineffective in NH4/+ salvage. In the deamination direction, despite the enhancement of the a-, and α-subunits by MSX, the basic charge isomers of GDH had very high K(m) value for L-glu (50 mM), similar to that (25 mM) of the control. Thus, the GDHs of the control, and MSX treatment could not function in the deamination reaction in vivo. These results show that the treatment of peanut with MSX impaired the amination function of GDH.
Osuji, G., & Madu, W. (1997). Regulation of peanut glutamate dehydrogenase by methionine sulphoximine. Phytochemistry, 46 (5), 817-825. https://doi.org/10.1016/S0031-9422(97)00395-6