Identification of protein-ribulosamine-5-phosphatase as human low-molecular-weight protein tyrosine phosphatase-A
Résumé
Ribulosamines, which are substrates for the deglycating enzyme fructosamine-3-kinase-related protein, are presumably formed intracellularly through glycation of proteins with ribose 5-phosphate followed by dephosphorylation of resulting ribulosamine 5-phosphates by a putative ribulosamine-5-phosphatase. Ribose 5-phosphate is known to be a potent glycating agent and we show in the present work that it reacts ≈ 10- and 80-fold more rapidly with protein than ribose and glucose, respectively. We also show that tissue and most particularly erythrocyte extracts contain a protein-ribulosamine-5-phosphatase. We have purified this enzyme from human erythrocytes to near-homogeneity and shown it to correspond to 'low-molecular-weight protein-tyrosine-phosphatase-A'. Human recombinant low-molecular-weight protein-tyrosine-phosphatase-A displayed a ribulosamine-5-phosphatase activity that was higher than its tyrosine-phosphatase activity, indicating that this phosphatase may participate in protein deglycation, a new form of protein repair.
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