ABCA1 is a membrane-bound protein that acts as a catalyst in the initial step of RCT. It facilitates the transfer of free cholesterol and phospholipids to lipid-poor apolipoproteins, primarily apoA-I, forming nascent HDL particles. This step is pivotal as it initiates the process of cholesterol efflux from cells, setting the stage for subsequent esterification by LCAT and transport back to the liver.
