## How do I calculate the number of thiol groups?

**Moderators:** honeev, Leonid, amiradm, BioTeam

### How do I calculate the number of thiol groups?

I did a purification protein experiment and for my report I need to determine the amount of thiol groups. For the absorbance value of standard ovalbumin, with SDS I got 0.142 and without SDS I got 0.09. I understand that with SDS the answer should be in or around 4 and without SDS it should be 0. The following information is what I'm given:

Use the equation: V x ΔA412 / ε x n

V is the volume of the sample, which is 3ml.

ΔA412 = Final ΔA412 - Initial ΔA412

ε is the molar extinction coefficient of DTNB (13.6 x 106 M-1

cm-1).

n is the molar quantity of ovalbumin in the sample (molecular weight of ovalbumin is

43 000).

The standard ovalbumin provided is (7.5 mg/ml)

If anyone could help figure how to work out the number of thiol groups. I would be much appreciated. Thank you in advance

Use the equation: V x ΔA412 / ε x n

V is the volume of the sample, which is 3ml.

ΔA412 = Final ΔA412 - Initial ΔA412

ε is the molar extinction coefficient of DTNB (13.6 x 106 M-1

cm-1).

n is the molar quantity of ovalbumin in the sample (molecular weight of ovalbumin is

43 000).

The standard ovalbumin provided is (7.5 mg/ml)

If anyone could help figure how to work out the number of thiol groups. I would be much appreciated. Thank you in advance

### Re: How do I calculate the number of thiol groups?

This is the way I would make the calculation. However I find something wrong in the numerical application. Is your eps OK ? I do not see why using V.

If I understand well the data your equation starts from the beer lambert equation: OD =eps x l x C where l is the length of the cuvette and C the concentration.

This gives C= OD/ eps x l C is the thiol concentration. usually l = 1 cm.

If z is the number of thiol per ovalbumin, the thiol concentration is therefore z x 7.5/43000 M

So z = C x 43000 /7.5 = OD x 43000 / eps x 7.5

OD is your delta 412, OD is optical density

If I understand well the data your equation starts from the beer lambert equation: OD =eps x l x C where l is the length of the cuvette and C the concentration.

This gives C= OD/ eps x l C is the thiol concentration. usually l = 1 cm.

If z is the number of thiol per ovalbumin, the thiol concentration is therefore z x 7.5/43000 M

So z = C x 43000 /7.5 = OD x 43000 / eps x 7.5

OD is your delta 412, OD is optical density

### Who is online

Users browsing this forum: No registered users and 16 guests