In contrast to other oxidative modifications of amino acids, methionine sulfoxide can be enzymatically reduced back to methionine in proteins by the peptide methionine sulfoxide reductase system, composed of MsrA and MsrB. The expression of MsrA and one member of the MsrB family, hCBS-1, was analyzed during replicative senescence of WI-38 human fibroblasts. Gene expression decreased for both enzymes in senescent cells compared to young cells, and this decline was associated with an alteration in catalytic activity and the accumulation of oxidized proteins during senescence. These results suggest that downregulation of MsrA and hCBS-1 can alter the ability of senescent cells to cope with oxidative stress, hence contributing to the age-related accumulation of oxidative damage.-link
Methionine intake has been linked to lifespan, methionine is said to be easily damageable. Methionine sulfoxide reductases help deal with this damage, yet it seems that senescence results in downregulation of these protective enzymes. Some say the regular aging process also results in reduction of production of these enzymes, along with the said increase in membrane peroxidation index, the cells would become more damage prone with increasing age. It is said every ten years, after approx maturity, there's a doubling of mortality. Why are changes that increase cellular damage taking place? It's clear that such changes might exceed the maintenance mechanisms of the cells and be behind this increased probability of death.
