While different types of annexins can function as membrane scaffolds, annexin A-V is the most abundant membrane-bound annexin scaffold. Annexin A-V can form 2-dimensional networks when bound to the phosphatidylserine unit of the membrane. Annexin A-V is effective in stabilizing changes in cell shape during endocytosis and exocytosis, as well as other cell membrane processes. Alternatively, annexins A-I and A-II bind phosphatidylserine and phosphatidylcholine units in the cell membrane, and are often found forming monolayered clusters that lack a definite shape.