Question

Using the total structure weight (= molecular weight) given in the PDB entry, calculate the molarity of a 0.3 mg/mL solution of a lactate dehydrogenase solution. You must state your chosen PDB entry ID

Answer 1

Lactic Dehydrogenase (LDH) has a total molecular weight of 140 kDa and is composed of 4 subunits which are designated M subunit (muscle) and H subunit (heart). These subunits may be mixed in any of 5 combinations (M4, M3H1, M2H2, MH3, and H4).

0.3 mg/mL = 0.3 g/L because: 1 g/L = 1000 mg/1000 mL = 1 mg/mL.

The molar amount of 0.3 g protein in 1 L (1 dm³) of solution is:

0.3/140000 = 0.00000214285 mol = 2.14 x 10^-6 mol/dm³

Therefore, the concentration is 2.14 x 10^-6 mol/dm³ (= 2.14 x 10^-6 M).