Increased lability of triosephosphate isomerase in progeria and Werner's syndrome fibroblasts.

Triosephosphate isomerase was found to have an increased thermolabile component in skin fibroblasts from patients with progeria and Werner's syndrome when compared with normal fibroblasts. Mixtures of cell extracts from progeria or Werner's syndrome with normal fibroblasts gave intermediate levels of the heat-labile triosephosphate isomerase suggesting the absence of cytosolic destabilizing factors. The incorporation of the protease inhibitors 1-tosylamide-2-phenylethyl chloromethyl ketone, N-alpha-p-tosyl-L-lysine chloromethyl ketone, phenylmethyl-sulfonyl fluoride, and pepstatin A in cell extracts failed to affect the level of the labile form of triosephosphate isomerase. The labile component also accumulates in normal fibroblasts in late passage in tissue culture and appears to be identical to the deamidated form of the enzyme which accumulates in other aging cells.