The yeast Pichia pastoris is a widely used host for recombinant protein expression, and has recently been engineered for whole-cell biocatalysis. The inducible P-AOX and constitutive P-GAP promoters are commonly employed. In this study, the S-adenosyl-L-methionine (SAM) biosynthesis and degradation efficiency of two P. pastoris strains were compared, and novel inhibitors that suppress SAM degradation were characterized. The strains exhibited clear physiological differences. P-GAP-Pichia showed higher transcription and activity of SAM synthetase, and the rapid cell growth led to higher levels of spermidine synthesis from SAM. In contrast, P-AOX-Pichia synthesized higher levels of glutathione from SAM, and this strain responded to hydrogen peroxide formation during methanol utilization. Aristeromycin proved an efficient inhibitor of SAM degradation in P-AOX-Pichia; 0.02 mg/L led to a 36.36% reduction in the ratio of glutathionine:SAM, and SAM accumulation was enhanced by 7.74% to 11.83 g/L. Ethanol was an even more efficient inhibitor of SAM consumption in P-GAP-Pichia; 8 g/L resulted in a 73.68% decrease in the ratio of SPD:SAM, and SAM production was elevated by 54.55% to 0.17 g/L/h. (C) 2013 Elsevier Inc. All rights reserved.