Role of polyol moiety of amphotericin B in ion channel formation and sterol selectivity in bilayer membrane.

Amphotericin B (AmB) is a polyene macrolide antibiotic widely used to treat mycotic infections. In this paper, we focus on the role of the polyol moiety of AmB in sterol selectivity using 7-oxo-AmB, 7α-OH-AmB, and 7ß-OH-AmB. The 7-OH analogs were prepared from 7-oxo-AmB. Their K(+) flux activity in liposomes showed that introduction of an additional ketone or hydroxy group on the polyol moiety reduces the original activity. Conformational analyses of these derivatives indicated that intramolecular hydrogen-bonding network possibly influenced the conformational rigidity of the macrolactone ring, and stabilized the active conformation in the membrane. Additionally, the flexible polyol leads to destabilization of the whole macrolactone ring conformation, resulting in a loss of sterol selectivity.

Triol protection with 6-benzoyl-3,4-dihydro-(2H)-pyran.

6-Benzoyl-3,4-dihydro-(2H)-pyran will protect 1,2,3-triols such as glycerol as their corresponding spiro-[5-phenyl-3,6,8-trioxabicyclo[3.2.1]octane-4,2[prime or minute]-tetrahydropyran]s and 1,2,4-triols (less efficiently) as the corresponding trioxabicyclo[3.2.2]nonanes; the hexol mannitol is converted into the corresponding bis-protected product.

Autocatalytic formation of a covalent link between tryptophan 41 and the heme in ascorbate peroxidase.

Electronic spectroscopy, HPLC analyses, and mass spectrometry (MALDI-TOF and MS/MS) have been used to show that a covalent link from the heme to the distal Trp41 can occur on exposure of ascorbate peroxidase (APX) to H2O2 under noncatalytic conditions. Parallel analyses with the W41A variant and with APX reconstituted with deuteroheme clearly indicate that the covalent link does not form in the absence of either Trp41 or the heme vinyl groups. The presence of substrate also precludes formation of the link. Formation of a protein radical at Trp41 is implicated, in a reaction mechanism that is analogous to that proposed [Ghiladi, R. A., et al. (2005) Biochemistry 44, 15093-15105] for formation of a covalent Trp-Tyr-Met link in the closely related catalase peroxidase (KatG) enzymes. Collectively, the data suggest that radical formation at the distal tryptophan position is not an exclusive feature of the KatG enzymes and may be used more widely across other members of the class I heme peroxidase family.