F-4900 FK-506, >98%
M.W. 804.02   C44H69NO12   [104987-11-3]
Storage:  Store at or below -20 ºC.  Solubility:  Soluble in DMSO at 100 mg/mL; soluble in ethanol at 100 mg/mL; very poorly soluble in water; maximum solubility in plain water is estimated to be about 10 µM; buffers, serum, or other additives may increase or decrease the aqueous solubility.  Disposal:  A
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Ascomycin level is less than 0.5%.
FK-506 is a potent immunosuppressant and in vitro T cell proliferation blocker.  It has been shown to disrupt calcineurin (also known as CaN or phosphatase 2B)-mediated signal transduction in T lymphocytes.  The compound interacts with its FK506-binding protein-12 (FKBP12).  The resulting complex, in turn, interferes with calcineurin substrate interaction.  Dumont, F.J.  "FK506, an immunosuppressant targeting calcineurin function."  Curr. Med. Chem. 7:  731-748 (2000).
FK-506 inhibits FKBP activity resulting in an increase in the release of sarcoplasmic reticulum-derived calcium.  FK-506 also appears to inhibit Na(+)-Ca2+ exchange.  Prolonged exposure of Xenopus A6 cells to FK-506 significantly inhibits aldosterone-stimulated Na+ transport and Na(+)-K(+)-ATPase activity.  Unlike rapamycin, which also binds to FK506-binding protein-12, FKBP12 with or without bound FK506 has no effect on rat brain PKC activity in vitro.  McCall, E., et al.