|Protein Name||Aldehyde dehydrogenase|
|Milk Fraction||MFGM, Exosome|
|Protein Existence Status||Unreviewed: Protein inferred from homology|
|Protein Function||Milk xanthine oxidase is an archetypal enzyme, which was originally described as aldehyde oxidase; catalyzes the oxidation of hypoxanthine to xanthine and xanthine to uric acid; source of superoxide ion, hydrogen peroxide, and nitric oxide, which can function as second messengers in the activation of various pathways; may induce mutagenesis, cell proliferation, and tumor progression, but they are also associated with apoptosis and cell differentiation; XOR activity generates free radicals and other oxidant reactive species resulting in either harmful or beneficial outcomes; modulate endothelial function and arteriolar tone; may be cytotoxic; catalytic role in the ALDH3 regulates biosynthesis of retinoic acid in mammary cells; ALDH activity plays a role in activating the luminal cell differentiation program in the mammary gland through retinoid signaling pathways|
|Biochemical Properties||Represents more than 8% of the intrinsic protein in MFGM;homodimer; oxidizes in the presence of NAD+ or NADP+ as electron acceptors; bacterial XDHs usually show better catalytic activity and thermal stability than eukaryotic XDHs but both display optimum catalytic activity at nearly neutral pH and relatively low temperatures, and very limit pH-activity range; mammalian enzyme exists in two interconvertible forms, xanthine dehydrogenase and xanthine oxidase; can be interconverted reversibly by sulphide reagents or irreversibly by proteolysis; specificity is low for methylene blue and 2.6-dichlorophenolindophenol, ferricyanide, and many quinones; inactive forms are demolybdo or desulfo; XOR inhibitors are allopurinol, oxypurinol or analogues|
|Significance in milk||Antimicrobial activity; natural antibiotic; encourages breas-feeding in infants; generates hydrogen peroxide;|
|PTMs||Glycosylated; 5 N-linked glycans; mixtures of high mannose, complex and hybrid type; 59 different structures have been identified till date; fucosylated and sialylated; presence of unusual motifs including N,N'-diacetyllactosamine as found in bovine milk|
|Significance of PTMs||Glycosylation changes at multiple points of lactation; glycosylation plays a role in the protein's bioactivity and its digestion profile in the infant gut; source of novel bioactives; stimulation of bone formation; anticancer; sialylation chelates loosed bound Ca2+ and prevent bacterial colonization|
|Bibliography||1. Blakistone, B. A., Sisler, E. C., & Aurand, L. W. (1978). Transport of Bovine Milk Xanthine Oxidase into Mammary Glands of the Rat. Journal of Dairy Science, 61(2), 168–175. https://doi.org/10.3168/jds.S0022-0302(78)83574-7. |
2. Enroth, C., Eger, B. T., Okamoto, K., Nishino, T., Nishino, T., & Pai, E. F. (2000). Crystal structures of bovine milk xanthine dehydrogenase and xanthine oxidase: structure-based mechanism of conversion. Proceedings of the National Academy of Sciences of the United States of America, 97(20), 10723–10728. https://doi.org/10.1073/pnas.97.20.10723.
3. Eirew, P., Kannan, N., Knapp, D. J. H. F., Vaillant, F., Emerman, J. T., Lindeman, G. J., … Eaves, C. J. (2012). Aldehyde dehydrogenase activity is a biomarker of primitive normal human mammary luminal cells. Stem Cells (Dayton, Ohio), 30(2), 344–348. https://doi.org/10.1002/stem.1001.
4. Arévalo Turrubiarte, M., Perruchot, M.-H., Finot, L., Mayeur, F., & Dessauge, F. (2016). Phenotypic and functional characterization of two bovine mammary epithelial cell lines in 2D and 3D models. American Journal of Physiology. Cell Physiology, 310(5), C348-56. https://doi.org/10.1152/ajpcell.00261.2015.