C'onfiirmutionul ,fk cnrrgy culciilutions using an empirical potential ECEPP/3 (Empirical Confbrmutional Energj? Program ,for Peptides, Version 3) wcrp carried oiit on angiotensin II ('4II) of'srqiicwc A,spArg-Val-T,~r-Ile-Hi.s-Pro-Phe to,find [he slahle conformarions ofthe,fiee stat(> in tho iinhjdratcd and thc hydrated states. A conformational analyris efthe unhvdmted state M'U.S c a r r i d out using thLj hiiildiip procediire. Thc>,fke mergy calciilation iising the hydration shtdl modc.1 was also carrid oiit to obtain the stable confiirmution of thcj hydrated state. Thc c ~l c t i l a t ~d stablc confi)rmution.s ofAII in both states have u purtiullj* right-handed a-hdical striiciim siabilixcl hj. short-and mediiim-range interactions. The similarity bet wivw the lowest . / r t ~ enrrgj3 c,ot7fi)rmations qf the imhydrated and hydrated .starcs siiggcsls [hat [hi. hydration might noi bc iniporiunt t o stabilize the overall confi)rmution o f A I I in u.frrcj .statci. The absence of'f'unj. intrumoli~Liilar intimction of the Tyr .si& chain siiggests thc po.s.sihlc interaction ofthis rrJ.sidiir with thr rcwplor. In [his stiidy, bve,fOund that the lott,,fice cnergy confiwnations contain both thcparullc~~-platc and thc perpt~ndiculur-plate geornc>trit.s of'thP His and Phe rings, suggesting tht. cot~,vistt~ncc~ ((both confimnations. 0 1996 John Wiley & Sons, Inc.