When a solution of glutamine is added to solid 1,1'-carbonyldiimidazole, a
mixture of oligo(glutamine)s up to about the 11-mer is formed rapidly. On s
tanding overnight, the solution deposits a precipitate that does not easily
redissolve. We have studied the inhibition of this precipitation by glutam
ine-containing peptides. We find that the alternating peptides (arg.gln)(4)
and (arg.gln)(8) are efficient inhibitors of precipitation while arg(5), (
glu.gln)(4), and a nonalternating octapeptide of the same composition as (a
rg.gln)(4) do not inhibit precipitation even though all the arg-containing
peptides readily adsorb to oligo(glutamine) precipitates. A possible struct
ural basis for this difference is discussed. (C) 2001 Academic Press.