Age-related alterations in the heat-stability of mouse heart phosphorylase

Myocardial phosphorylase from young and old mice has been examined with respect to its thermal lability properties. It has been shown that phosphorylase from the hearts of old animals is more resistant to heat as compared to the enzyme from young hearts. This increase in thermal stability seems to be correlated with an increase in the less active tetrametric form of the enzymes during aging. Sucrose density centrifugation profiles indicate that upon heating the amount of dimer stays relatively constant in the old heart since the tetramer is probably being broken down into its more active dimeric form. This increase in the tetrameric form of phosphorylase in the old heart may help to explain the increased susceptibility of the old heart to many acute stresses.