Changes in membrane-bound leucine aminopeptidase activity during maturation and ageing of brain

Aminopeptidases are believed to be enzymes that regulate the activity of va rious neuropeptides. However, their physiological role, as well as their me chanisms of regulation, are not well understood. To analyze a part of the r egulatory mechanisms that control the activity of these enzymes, the subcel lular distribution of membrane-bound leucyl aminopeptidase activity was stu died in rat brain during development and ageing. Except in fetuses, the enz ymic activity was greatest in the microsomal fraction in all ages tested. E xcept in microsomal and myelin fractions, compared with fetuses, leucyl ami nopeptidase activity showed a decrease in 1-week-old rats and a subsequent increase to adult levels in I-month-old rats. This profile differed in the microsomal fraction, where the activity increased steadily up to 1-month-ol d rats. After this age, the activity decreased progressively in 5-month and 24-month-old rats. These results may reflect changes in the functional sta tus of the susceptible substrates during development and ageing.