| Lactate dehydrogenase B (LDH‑B, LDHB) is the B subunit of the lactate dehydrogenase family of cytosolic oxidoreductases and forms part of the tetrameric LDH isoenzymes that catalyze the reversible interconversion of pyruvate and lactate with concomitant interconversion of NADH and NAD⁺, functioning at the interface of glycolysis and oxidative metabolism in many tissues. The B subunit is enriched in aerobic tissues such as heart and oxidative skeletal muscle and favors the oxidation of lactate to pyruvate, supporting routing of carbon into the tricarboxylic acid cycle and oxidative phosphorylation when oxygen availability and mitochondrial capacity are high. LDH‑B operates as a soluble cytosolic enzyme with additional localization reported at the inner mitochondrial membrane and in extracellular vesicles, placing it in positions where it can couple cytosolic NAD⁺/NADH balance, lactate–pyruvate shuttling, and intercellular exchange of metabolic signals. The catalytic mechanism involves ordered binding of NAD⁺/NADH and pyruvate/lactate in the active site and stereospecific hydride transfer that links lactate production or consumption directly to redox balance and thus to pathways that depend on cytosolic NAD⁺ regeneration or NADH utilization. LDH‑B expression and activity shape lactate handling and mitochondrial function in muscle by promoting conversion of lactate to pyruvate, and transcriptional programs driven by PGC‑1α and estrogen-related receptor α selectively induce LDH‑B while repressing LDH‑A, aligning LDH isoform composition with oxidative muscle remodeling and whole‑body lactate homeostasis during endurance adaptation. LDH‑B participates in the bidirectional control of pyruvate and lactate levels together with LDH‑A, and knockdown of LDH‑B in breast cancer cells reduces total LDH activity, extracellular lactate accumulation, and cell motility, linking LDH‑B–dependent lactate metabolism to invasive behavior in endocrine‑resistant contexts. LDH‑B levels and activity contribute to the metabolic plasticity of tumor cells by modulating the balance between glycolytic flux, lactate export, and oxidative metabolism, and altered LDH‑B expression is reported in several cancers, including endocrine‑resistant breast and pancreatic tumors, where higher LDH‑B expression correlates with disease features and is required for efficient tumor growth in pancreatic cancer models. |
