As inferred from the yeast TIM8:TIM13 complex, the human TIMM8:TIMM13 complex chaperones hydrophobic membrane proteins in the intermembrane space until their insertion into the inner or outer membrane. In yeast experimentally verified substrates of the TIM8:TIM13 complex include TIM23 (TIMM23 in human) and TOM40 (TOMM40 in human). Many other mitochondrial proteins are anticipated to be chaperoned by the TIMM8:TIMM13 complex.