Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:ATP7A and ATP7B are P1B-type ATPases, which use the energy released from ATP hydrolysis to transport Cu across Golgi membranes (Jayakanthan et al. 2017; Lutsenko et al. 2008; Yatsunyk and Rosenzweig 2007; Yu et al. 2017b).
Category: