Ms. Almansa et al., CHARACTERIZATION OF AN IRON-CONTAINING SUPEROXIDE-DISMUTASE FROM A HIGHER-PLANT, CITRUS-LIMONUM, Physiologia Plantarum, 90(2), 1994, pp. 339-347
An iron-containing superoxide dismutase (SOD, EC 1.15.1.1) was fully c
haracterized from leaves of the higher plant Citrus limonum R. cv. Ver
na. This enzyme is the first iron-containing SOD to be characterized i
n the plant family Rutaceae. The purified Fe-SOD has a molecular mass
of about 47 kDa and is composed of two non-covalently joined equal sub
units. The amino acid composition determined for the enzyme was compar
ed with that of a wide range of SODs and had highest degree of homolog
y with the Fe-SODs from Brassica campestris and Nuphar luteum. The enz
yme was more labile at high temperatures than some eucaryotic and proc
aryotic Fe-SODs. It showed a maximum stability at pH 7.8. The sensitiv
ity of the enzyme to cyanide, hydrogen peroxide and o-phenanthroline w
as similar to those reported for other Fe-SODs, but the lemon enzyme w
as comparatively resistant to H2O2. By kinetic competition experiments
, the rate constant for the disproportionation of superoxide radicals
by lemon Fe-SOD was found to be 1.9 x 10(9) M-1 s-1 at pH 7.8 and 25-d
egrees-C. A comparative study between the molecular properties of this
higher plant Fe-SOD and SODs from different origins is presented.