Help with SOD calculation!

tsir tsir at
Fri Aug 7 05:19:46 EST 1998

I want to measure the SOD activity in five tobacco varieties. I followed up
the instruction of Dhinsda et al., method based on the inhibition of
nitrotetrazolium blue reduction by superoxide radicals (produced by light
mediated generation from riboflavin and methionnine).
In brief:
I made the reaction mixture
for any variety: From 0.5 gr FW of tobacco leaf  I made 8 ml enzyme
In the final step I have the control sample S0 (that does not contain enzyme
extract) and five other samples S1, S2, S3, S4, S5,  coming from five
different tobacco varieties, that contain 40 nl enzyme extract. These
samples were exposed to light for 10 minutes. The absorption of these
samples was measured using as blank the respective samples so, s1...s5, held
in the dark for 10 minutes also. The absorbencies were:
S0= 0.300, S1=0.297, S2=0.225, S3=0.210, S4= 0.150 and S5=0.075
Now, how can I calculate the SOD activity? In same papers I found the
expression "One unit of SOD is equivalent to 50% inhibition of reduction of
nitrotetrazolium blue". But what does this mean in the action? and how can I
calculate the SOD activity of S1 ... S5 samples?
Thank you in advance

Constantine Saitanis

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