N. Ohta et al., EFFECT OF TRANS-DIAMMINEDICHLOROPLATINUM(II) ON HUMAN SERUM-ALBUMIN -CONFORMATIONAL-CHANGES THROUGH PARTIAL DISULFIDE BOND-CLEAVAGE, International journal of pharmaceutics, 118(1), 1995, pp. 85-93
trans-Diamminedichloroplatinum(II) (trans-DDP), the trans isomer of ci
s-diamminedichloroplatinum(II) (cis-DDP), was bound to human serum alb
umin (HSA) in pH 7.4 buffer containing 0.1 M NaCl at 37 degrees C. The
amount of bound trans-DDP per mol of HSA was found to be 21.4 mol whe
n the protein was incubated with a 40-fold excess of trans-DDP for 6 d
ays, In trans-DDP-treated HSA, 3.4 disulfide (S-S) bonds were cleaved,
where one HSA molecule contains 17 S-S bonds. The spectral characteri
stics of trans-DDP-treated HSA were examined in terms of the fluoresce
nce spectrum of its lone tryptophan (Trp-214), and molar ellipticity.
The relative fluorescence intensity of platinum-bound HSA decreased to
32.4% of that of the native state, suggesting that perturbation aroun
d the Trp-214 residue took place. This was confirmed by the destructio
n of the warfarin-binding site containing Trp-214 observed in the meta
l-bound HSA. Analysis of circular dichroism (CD) spectra showed a decr
easing helix content from 50.5% in the native state to 30.6% in the me
tal-bound HSA. These conformational changes observed in HSA may be att
ributed to the S-S bond rupture induced by trans-DDP. Comparison with
cis-DDP, which has already been shown to cleave S-S bonds in HSA, reve
aled that trans-DDP binds to HSA and cleaves S-S bonds more readily th
an the cis isomer.