The function of Nα‐acetylation of the eye‐lens crystallins

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Abstract
The putative protective role of the N.alpha.-acetyl group of proteins was investigated. Synthetic, non-acetylated N-terminal tetrapeptides of the .alpha.A2- and .gamma.II-crystallin chains [from calves] are good substrates for leucine aminopeptidase, while the acetylated ones are completely resistant. In the native, non-acetylated, .gamma.-crystallin the N terminus is not degraded by leucine aminopeptidase. Newly synthesized .alpha.A2-crystallin, in which the normally occurring N-terminal acetylation was prevented during cell-free translation, is virtually resistant against degradation by leucine aminopeptidase. Only at extreme enzyme-substrate ratios the N-terminal methionine is removed. Although the N.alpha.-acetyl group by its very nature protects against this exopeptidase, the group may not be essential for this purpose in the native crystallins.