These results unambiguously demonstrate that a single amino acid residue substitution is sufficient to generate a phenylalanine - insensitive form of arog . furthermore , the mutant a ( l - 15 ) lacking the first fifteen n - terminal amino acid residues exhibits no sensitivity toward phenylalanine in a range of 0 ~ 1 mm phenylalanine 這些結(jié)果揭示: 1 ) n一末端在反饋抑制機理中具有重要作用; 2 ) n一末端的缺失使得ar0g緊密二聚體結(jié)構(gòu)解聚,導(dǎo)致四級結(jié)構(gòu)破壞。