Radiation inactivation analysis

From biochemical studies after in vitro isolation, NADH NR appears to be a soluble homodimeric enzyme (Pan Nason, 1978 Solomonson Barber, 1990), aggregating into tetramers at high concentration, as has been described in Chlorella and occasionally observed in higher plants. Both subunits (molecular mass 100-110 kDa) have recently been shown to be linked by a disulphide bond which can be reduced without loss of activity (Hyde et al., 1989). There is no direct evidence that a monomer subunit alone is active. Nevertheless, radiation inactivation analysis (Solomonson et al., 1987) provided a target size for Chlorella and spinach NADHrNR of 100 kDa, suggesting that indeed each subunit would behave independently as a functional NADH NR unit. 

Solomonson, L.P., McCreery, M.J., Kay, C.J. Barber, M.J. (1987). Radiation inactivation analysis of assimilatory NADH nitrate reductase apparent functional sizes of partial activities associated with intact and proteolytically modified enzyme. Journal of Biological Chemistry 262, 8934-9. 

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