It is being recognized that an amino acid sequence c taining onlya subset of the 2Q naturallyoccurri amino acids can tiefine a native protein structure . To test this hypothesis . we des「 gned and prQduoed an active trypsin inhibitor that iscomposed of onIyg residue types. this9 − reslduE −type inhibitor sequenc θ was rat 「 onalIy designed based on the s θquence of Bovine Pancreat [ c Tr ゾ psin lnhibitor ( BPTI > , andby repleclngAandTwithA ;RandKwith R; EorDntlthE : L , V, 1, MwithL ; F, Y, W、

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... Hwi 主hF ; N. Q、 S for N; and keeping C, P, G, A totalof twenty mutatiens were inヒroduced follewing the above scheme . Sedimentation θqui 目brlum experiments 「 ndicate that thls 9−residue −type lnhibitor is monomeric , and CD θxperimen 亡s shovv that thismoleoulemelts cDoPerativeTywith a midPQint tempera 亡 ureof 45C. T 1D − NMR sp θ ctrum isnativelIke , and 2D−NOESY spectrumsugg θ sts that the twobeta strands existl in the structureof thenative ee丁l remainstructured inthg motant ・ The activity of this 9 − fesidue − type trypsin inhibltor ls sira 口 ar to that of BPTI. This is a further lndiGation that thestr 凵 ctureof this9