As a part of our program to assess the effect of blood components to the drug delivery capabilities of phospholipid vesicles, we have studied the binding of human high density lipoprotein A-1 protein with phosphatidylcholine vesicle. Binding experiments were conducted by using the ultracentrifugation method with phospholipid to protein molar ratio between 1000 to 5000. It was found the extent of binding increased slowly in the range of phospholipid to protein ratio 2500 to 1000. In order to monitor the size change induced by binding, the complexs between apo A-1 and phospholipid were passed through a sepharose CL-4B column. There was no change in vesicle size in the range of phospholipid to protein ratio 3500 to 5000. On the other hand, an appreciable size decrease was observed below the ratio of 3000. There observation suggest that at high apo A-1 concentration, the vesicles are converted into a form of smaller size and that there two form of phospholipid aggregates have differed apo A-1 binding behavior.
The binding parameters of apo A-1-phospholipid vesicle interaction were determined from the double reciprocal plot. This plot was also consistent with the above conclusion.
Permiability test was performed to determined the effect of added apo A-1 and the temperature. There was a 56% increase in the permeability by increasing the temperature from 37℃ to 44.5℃. In presence of 0.24 μg/ml apo A-1, the increase in the permeability was 58% over the control value in the absence of the apo A-1.
1. Binding test 결과를 보면, lipid/protein molar ratio 가 5,000 에서 3,000 일때는 binding 양이 서서히 증가 하다가, 2,500 에서 1,000 일때는 급증 하였다.
2. Gel filtration 결과를 보면, lipid/protein molar ratio가 3,500 에서 5,000 까지는 vesicle 의 size 변화가 거의 안 보이다가, 3,000 이하 에서는 size 의 감소가 일어났다.
3. 이런 observation 에서 우리는 protein 이 고농도로 존재 할때와 저농도로 존재할때 vesicle에 binding behavior 가 다르다는 것을 알았다.
4. Permeability test 결과에서 보면, 37℃에서 44.5℃ 로 변화함에 따라서 56% 의 permeability 증가가 보였으며, 0.24 μg/ml apo A-l 을 addition 한에 따라서 58% 가 증가 하였다.
