Explain Protein - Lecithin Theory.

Explanation

1. In 1956, Bennet - Clark proposed that the carrier could be a protein associated with the phosphatide called as lecithin.
2. The carrier is amphoteric ( the ability to act either as an acid or a base ) and hence both cations and anious combine with it to from Lecithin -ion complex in the membrane.
3. Inside the membrane the Lecithin - ion complex is broken down into phosphatidic acid and choline along with the liberation of ions.
4. Lecithin again gets regenerated from phosphatidic acid and choline in the presence of the enzyme choline acetylase and choline estrase.
5. ATP is required for regeneration of lecithin.