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:Serine hydroxymethyl-transferase (SHMT) has been shown to catalyze the inversion of glycine and serine [33], but in the present experiment, SHMT, was a highly light induced protein closely concerned with the photorespiratory pathway [34].
Category: