C-P4H activity was analyzed from P. pastoris cell pellets that were broken with zirconia beads in basic conditions. The activity assay is based on the hydroxylation-coupled decarboxylation of 2-oxo [1-14 C] glutarate with (Pro-Pro-Gly) 10 as the peptide substrate [26] . The total protein concentrations were determined with the RC DC Protein assay Kit (Biorad Laboratories).