Lecture 5

Question 1

How is valinomycin structured

Answer 1

Ring structure

D- and L-valines, lactic acid and hydroxyvaleric acid

K+ bound to centre of ring

K+ bound by carbonyl oxygens

Outer perimiter lipophilic

Selective for K+ over Na+

Question 2

Why does valinomycin select for K+ over Na+

Answer 2

K+ has lower free energy of dehydration

Question 3

Explain valinomycin mechanism

Answer 3

1. Valinomycin carries K+ across cell membrane after forming carrier-substrate complex
2. CS is re-oriented to align binding site to inside
3. K+ released
4. Empty carrier re-orientates to align binding site to outside

Steps 1 and 3 refer to binding and release of substrate

Steps 2 and 4 refer to rate of carrier to re-orientate binding site

Question 4

GLUT1 pathway

Answer 4

1. Glucose binding site faces outwards and posied to bind glucose
2. Glucose binds
3. GLUT1 undergoes a conformational change to orientate binding site to face inwards
4. Glucose released, GLUT1 re-orientates to expose the binding site to the outside