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:Some proteases have been implicated in the degradation of extracellular proteins and the acquisition of amino acids for cellular growth (Park et al. 2004), and mutation of such proteases may have a harmful effect on cellular growth (Vitikainen et al. 2005).
Category: