Publication Date:
2004-01-05
Description:
Protein disulfide isomerase (PDI) is known to contain the thioredoxin box motif with a low pKa cysteine residue. To investigate the reactivity of PDI with thiol modifiers at low physiological pHs, either the reduced (PDI[red]) or oxidized form (PDI[oxid]) of PDI was exposed to various alkylating ragents. When PDI was incubated with iodoacetamide at pH 6.3 for 30 min at 38C, a remarkable inactivation (〉90%) of PDI[red] was caused by iodoacetamide (IC[50]=8 M). However, PDI[oxid] was only slightly inactivated (approximately 18%) by iodoacetamide. Similarly, PDI[red] was significantly inactivated by Nethylmaleimide (NEM), but PDI[oxid] was not. When the inactivation by these alkylators was analyzed by pseudofirst order kinetics, NEM (k[3]=1.7510[-2] s[-1]; K[i]=124 M) was observed to be more potent than iodoacetamide (k[3]=9.110[-3] s[-1]; K=311 M). Interestingly, the inactivation of PDI[red] by iodoacetamide was greater at pH 6.3 than pH 7.0, in contrast to a similar inactivation potency of NEM at both pHs. Moreover, the maximal inactivation of PDI[red] or PDI[oxid] by iodoacetamide was mainly observed around pH 6.0. In addition, PDI[red] was found to be inactivated by acrolein (IC[50]=10 M) at pH 6.3, and this inactivation was also greater at pH 6.3 than at pH 7. Based on these results, we suggest that PDI[red] is susceptible to inactivation by alkylators including endogenous α,β-unsaturated aldehydes at low physiological pHs.
Print ISSN:
1431-6730
Electronic ISSN:
1437-4315
Topics:
Biology
,
Chemistry and Pharmacology
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