Dynamin-related GTPase that is essential for normal mitochondrial morphology by regulating the equilibrium between mitochondrial fusion and mitochondrial fission. Binds lipid membranes enriched in negatively charged phospholipids, such as cardiolipin, and promotes membrane tubulation. The intrinsic GTPase activity is low, and is strongly increased by interaction with lipid membranes (By similarity). Plays a role in remodeling cristae and the release of cytochrome c during apoptosis (By similarity). Inactive form produced by cleavage at S1 position by oma1 following stress conditions that induce loss of mitochondrial membrane potential, leading to negative regulation of mitochondrial fusion. GTP + H2O = GDP + H(+) + phosphate Oligomeric complex consisting of membrane-bound and soluble forms of OPA1. Binds PARL (By similarity). Detected at contact sites between endoplasmic reticulum and mitochondrion membranes. Strongly expressed in the brain, ovary and skeletal muscle. In the brain, expression of the mRNA was observed specifically in motor neurons, in nucleus oculomotorius, in nucleus valvulae lateralis, in the medulla oblongata and in the spinal cord. PARL-dependent proteolytic processing releases an antiapoptotic soluble form not required for mitochondrial fusion. Cleaved by oma1 at position S1 following stress conditions. Belongs to the TRAFAC class dynamin-like GTPase superfamily. Dynamin/Fzo/YdjA family.