09-214 Physical Chemistry Name______KEY___[10 pts total]______

Quiz 8 April 6, 2001

N_Avog = 6.022 X 10²³/mol

1 cycle = 2p radians

An enzyme tenysase has a molecular weight of 70,000 and a v₂ = 0.725 cm³/g at 20^oC. Boundary sedimentation in a dilute, aqueous pH 6.6 buffer (density = 1.015 g/cm³) at 20^oC and a speed of rotation of 54,400 rpm gave the following results

The sedimentation coefficient s is related to solute and solvent properties through

s = (2.303/w²)(d log x _1/2 /dt) = m(1-v₂p)/f

Calculate s (with units). [5 pts]

dlogx/dt = (.7929-.7797)/(60m-20m) = 3.3 X 10^-4 m^-1 from the first two data, for example (2 pts partial)

w = 54500 rpm (2p radians/revolution) = 3.41 X 10⁵ rads/m (2 pts partial)

s = (2.303/[3.41 X 10⁵ m^-1]²)(3.3 X 10^-4 m^-1) = 6.63 X 10^-15 m

( or 3.98 X 10^-13 sec )

Calculate the frictional coefficient of the enzyme in the given medium. [5 pts]

f = m(1-v₂ p)/s

m = (70000 g/mol)/(6.022 X 10²³ molecules/mol) = 1.162 X 10^-19 g/molecule (2 pts partial)

f = 1.162 X 10^-19 g (1 - [0.725 cm³/g][1.015 g/cm³])/(3.98 X 10^-13 sec) = 7.71 X 10^-8 g/sec