Oncocytomas are epithelial tumors characterized by an accumulation of structurally and functionally compromised mitochondria, with a generally benign prognosis. The genetic causes behind oncocytic transformation are still unknown; therefore, the study of oncocytomas in syndromic familial contexts is particularly useful in the search for the genetic determinants of this phenotype. Several members of a family affected by hyperparathyroidism-jaw tumor syndrome (HPT-JT), due to a large deletion in CDC73, had recurrence of oncocytic parathyroid tumors. Exome sequencing ruled out private family mutations; however, within the inherited deletion, regulatory elements of the glutaredoxin 2 (GLRX2) gene have been identified. This gene encodes a mitochondrial isoform responsible for reversible protein deglutathionylation –a modification that modulates the activity of various targets- whose role in cancer is still unknown. The protein was absent in all tumors and halved in the healthy tissues of the subjects. To investigate whether its absence alters protein deglutathionylation predisposing to the oncocytic phenotype, TPC1 and HCT116 GLRX2 KO cell models were generated in which a reduced proliferative rate and altered glutathionylation of the proteome were found, particularly following oxidative stress. A pilot in vivo experiment showed oncocytic-like KO cells, with numerous altered mitochondria, consolidating the hypothesis that the redox alteration triggered by the absence of GLRX2 may induce a mitochondrial metabolic dysfunction mimicking those observed in oncocytomas. Proteomic analysis identified different glutathionylation targets in the KO samples such as proteins of the Krebs cycle and mitochondrial respiratory chain. Marked glutathionylation of the pyruvate dehydrogenase complex (PDHc) was correlated with a reduction in pyruvate-dependent ATP synthesis rate. Given the importance of oxidative stress in cancer pathophysiology and the role of glutathione in antioxidant response and protein function, GLRX2 represents a potential candidate in the regulation of oxidative metabolism in cancer cells exposed to stress and in the modulation of tumor phenotype.