Final answer:
The F1 subunit of ATP synthase is responsible for ATP synthesis; it contains the catalytic site and is not a proton pump, does not anchor the synthase to the membrane, nor is it involved in electron transport.
Step-by-step explanation:
The F1 subunit of ATP synthase characterizes as it contains the catalytic site for ATP synthesis. ATP synthase is a complex enzyme composed of two main parts, the Fo and the F1 subunits. The F1 subunit, which is situated within the mitochondrial matrix, is responsible for the synthesis of ATP from ADP and inorganic phosphate (Pi). It does not function as a proton pump nor is it directly involved in electron transport; instead, proton flow through the Fo portion, which is embedded in the inner mitochondrial membrane, causes the central stalk of the F1 unit to rotate, facilitating the enzymatic activity that synthesizes ATP.