金屬輔因子生化（bioinorganic chemistry / metalloenzymology）揭示了金屬離子如何被嚴格調控（metalloregulation），以及金屬穩態失衡如何導致疾病。
Fe-S Cluster Biogenesis
ISC machinery（mitochondrial）：scaffold protein ISCU + cysteine desulfurase NFS1（provides S from Cys）+ frataxin（iron donor, controversially）+ electron donor (ferredoxin)。ISC assembly defects 導致：
- Friedreich ataxia：frataxin（FXN）GAA trinucleotide repeat expansion → FXN↓↓ → Fe-S cluster assembly↓ → mitochondrial Fe accumulation + aconitase/ETC 活性↓ → cardiomyopathy + progressive ataxia。唯一 FDA 核准治療：omaveloxolone（Nrf2 activator, 2023）。
- ISCU myopathy（rare, Swedish/Finnish founder mutation）：ISCU splicing defect → exercise intolerance + myoglobinuria。
- Sideroblastic anemia with Fe-S cluster defect：GLRX5 mutation → Fe-S assembly↓ → ALAS2 (δ-aminolevulinate synthase, Fe-S enzyme) activity↓ → heme synthesis↓ → ringed sideroblasts。
CIA pathway（cytosolic iron-sulfur assembly）負責 cytosolic 和 nuclear Fe-S protein maturation（如 DNA polymerases, helicases, ABCE1）。
Hepcidin-Ferroportin Axis 的分子細節
Hepcidin（HAMP gene, 25 aa peptide）binding to ferroportin → JAK2-dependent phosphorylation → ubiquitination → endocytosis + lysosomal degradation。
Hepcidin 的轉錄調控：
- BMP-SMAD pathway（iron sensing）：hepatocyte 膜上 TfR2 和 HFE 感應 holo-transferrin → 調控 BMP6 → SMAD1/5/8 → hepcidin↑。HFE mutation（C282Y, H63D）= hereditary hemochromatosis → hepcidin↓ → iron overload。
- IL-6-JAK-STAT3 pathway（inflammation sensing）：hepcidin↑ → functional iron deficiency → anemia of inflammation。
- Erythropoietic demand：erythroferrone（ERFE, produced by erythroblasts）→ suppress BMP-SMAD → hepcidin↓ → iron mobilization for erythropoiesis。In β-thalassemia major（ineffective erythropoiesis）：ERFE↑↑ → hepcidin↓ → iron overload despite anemia。
Wilson Disease 和 Copper Homeostasis
ATP7B（hepatocyte Cu transporter）mutation → Cu 不能被排入膽汁或併入 ceruloplasmin → Cu 在肝臟和腦（特別是 basal ganglia）累積。臨床：肝病（急性肝衰竭 to 慢性肝硬化）+ neuropsychiatric（dystonia, tremor, personality change）+ Kayser-Fleischer ring（corneal Cu deposits）。Diagnosis: low ceruloplasmin + high urinary Cu + liver Cu >250 μg/g dry weight。
Treatment: (1) D-penicillamine（Cu chelator, 但副作用多）; (2) trientine（更好的 chelator）; (3) zinc acetate（inhibit Cu absorption by inducing metallothionein in enterocytes）; (4) liver transplant（definitive cure, also gene therapy trials underway）。
Selenocysteine — the 21st Amino Acid
Selenocysteine（Sec, U）是 co-translationally 插入蛋白質的，需 UGA codon recoding + SECIS element（3'-UTR stem-loop in eukaryotes）+ specialized elongation factor eEFSec + Sec-specific tRNA（tRNA^Sec）。25 human selenoproteins 包含 GPx1-4, TrxR1-3, DIO1-3（thyroid hormone activation/inactivation）。
Selenoprotein P（SELENOP）是 Se transport protein，含 10 Sec residues。SELENOP KO mice develop neurological 和 male fertility 缺陷 → Se distribution prioritizes brain and testes。
文獻：Rouault, T.A. (2015) Nat Rev Mol Cell Biol 16:45. / Muckenthaler, M.U. et al. (2017) Cell 168:344. / Kryukov, G.V. et al. (2003) Science 300:1439.