Human lens enzyme alterations with age and cataract: glyceraldehyde-3-P dehydrogenase and triose phosphate isomerase.
The isoelectric point distribution of G-3-P DH and TPI from human lenses was examined as a function of age and cataract formation. Both enzymes exhibited progressive heterogeneity with age and a shift towards an acidic charge. Little qualitative differences in the pI profiles of G-3-P DH and TPI were found to distinguish mixed cataracts from age comparable normal lenses. While the most alkaline form of G-3-P DH required less HAsO4= for optimal activity, no other kinetic property, i.e. Km substrate, cofactor and inhibitors distinguished any of the charge forms of G-3-P DH. All metaor isozyme forms of TPI had the same Km substrate in the forward and reverse reaction direction. The most acidic forms of G-3-P DH and TPI were less stable to increased temperatures than their more alkaline counterparts suggesting a decreased stability.
D000293:Adolescent; D000328:Adult; D000375:Aging; D002238:Carbohydrate Epimerases / Q000378:metabolism*; D002386:Cataract / Q000201:enzymology*; D002648:Child; D005260:Female; D005333:Fetus; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases / Q000378:metabolism*; D006801:Humans; D007223:Infant; D007525:Isoelectric Focusing; D007908:Lens, Crystalline / Q000201:enzymology / Q000254:growth & development*; D008875:Middle Aged; D011247:Pregnancy; D013816:Thermodynamics; D014305:Triose-Phosphate Isomerase / Q000378:metabolism*
D005987:Glyceraldehyde-3-Phosphate Dehydrogenases; D002238:Carbohydrate Epimerases; D014305:Triose-Phosphate Isomerase