Mechanism
The method combines the reactions of copper ions with the peptide bonds under alkaline conditions with the oxidation of aromatic protein residues. The Lowry method is best used with protein concentrations of 0.01-1.0 mg/ml and is based on the reaction of Cu+, produced by the oxidation of peptide bonds, with Folin-Ciocalteu reagent (a mixture of phosphotungstic acid and phosphomolybdic acid in the Folin-Ciocalteu reaction). The reaction mechanism is not well understood, but involves reduction of the Folin-Ciocalteu reagent and oxidation of aromatic residues (mainly tryptophan, also tyrosine).
1.1Preparation of Lowry reagent by mixing reagent A:B:C in the following ratio: 100 ml:1ml:1ml
A: 2% Na2CO3 ใน 0.1 N NaOH
B: 2% NaK Tartrate
C: 1% CuSO4 5(H2O)
1.2 Proceed experiments according to the following steps
Solution (ml)
Standard solution Sample
Blank 1 2 3 4 5
BSA 200 mg/l - 1ml 2
ml 3
ml 4
ml 5
ml
Sample - - - - - -
Distilled H2O 5 4 ml 3
ml 2
ml 1
ml -
Concentration (g/ml) 0 40 60 80 100 120
1.3 Pipette 0.5 ml of the solution from tube no. blank, 1-5 to new tubes
1.4 Add 0.7 ml of Lowry reagent to test tubes prepared in 1.3, incubate at room temp. for 10 min
1.5 Prepare working solution of Folin reagent by diluting it with distilled H2O in a ratio of 1:1
1.6 Add 0.1 ml of Folin reagent (working solution)in test tubes, mix, and incubate at room temp for 30 mins
1.7 Measure optical density (OD) at 600 nm
2. Enzyme extraction and Kinetic parameter assay
2.1 To a chilled motar, add 20g washed cell paste
2.2 Prepare 40g of quartz sand (SiO2) to add when grinding