Question

The myoglobin content of some human muscles is about 8 g/kg. In sperm whales, the myoglobin content of muscle is about 80 g/kg.

(a) How much O2 is bound to myoglobin in human muscle and in sperm whale muscle? Assume that the myoglobin is saturated with O2, and that the molecular weights of human and sperm whale myoglobin are the same.

(b) The amount of oxygen dissolved in tissue water (in equilibrium with venous blood) at 37 C is about 3.5 x 10^-5M. What is the ratio of oxygen bound to myoglobin to that directly dissolved in the water of sperm whale muscle?

The answer to (a) should be 0.0144g in humans and 0.144g in sperm whale and (b) should be 128. Please show me how to do it.

Answer 1

Molar mass of myoglobin : use a rounded value 17.5 kDa or 17 500 g/mol

(please verify if you use the same value)

8 g myoglobin/kg / 17 500 g/mol = 4.57 x10^-4 mol of myoglobin / kg human muscle.

Myoglobin (Mb) binds 1 oxygen molecule per molecule of protein, the molar ratio O2: myoglobin is 1:1.

For human muscles:

4.57 x10^-4 mol myoglobin mol / kg human muscle x 32 g O2/mol =146x 10^-4 gO2 /kg human muscles = 0.0146 g myoglobin / 1 kg human muscles (and also for O2 content of human muscles)

.

For sperm whales muscles:

(80 g myoglobin/kg / 17 500 g/mol) ) x 32 g O2/mol = 0.146 g myoglobin / 1 kg sperm whales muscles

b.

3.5x 10^-5 mol O₂/L x 32 gO₂/mol = 0.00112 gO₂/L

Ratio

0.146 g myoglobin / kg / 0.00112 gO₂/L = 130

Note : You have to use 17.77 kDa for Molar mass of myoglobin to obtain the results proposed by you (0.0144   / 0.144 / 128)