Early endosomes transform into late endosomes through a process called the maturation of endosomes. The early endosome moves from the periphery of a cell towards the perinuclear region. It first loses its tubular domains, and its vacuolar domain becomes roughly circular. The endosomal membrane buds inwards to form numerous vesicles called intraluminal vesicles or ILVs. Hence, maturing endosomes are also known as multivesicular bodies or MVBs. In addition, the trans-Golgi network delivers acid hydrolases and tethering proteins, such as SNAREs, to the maturing endosomes through vesicles. V-type ATPases pump protons from the cytosol into the endosomal lumen, lowering the pH and activating the acid hydrolases. Altogether, these changes are followed by the fusion of several endosomes with each other. The fusion increases the overall size and the number of intraluminal vesicles of the late endosome. The late endosome then fuses with a lysosome to form an endolysosome. The acidic environment of the endolysosome helps maintain the activity of the acid hydrolases, which actively degrade the endocytosed ligand with the aid of lysosomal enzymes.