The structure of the 32-residue peptide salmon calcitonin (sCT) in 90% MeOH-10% H2O has been investigated by two-dimensional NMR techniques and molecular modeling. Sequential assignments for nearly all of the 32 spin systems have been obtained, and results indicate that the heptaresidue loop formed by the disulfide bond between Cys-1 and Cys-7 is followed by an alpha-helical segment from Val-8 through Tyr-22. A region of conformational heterogeneity is observed for residues 20-25, resulting from the slow isomerism of the cis and trans forms of Pro-23. The C-terminal segment is found to exist in an extended conformation.

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INHIBITION OF OVULATION 457 the color reaction, the liquid was treated with Folin's tungstic acid reagent and the tests carried out on the filtrate. The analytical results were: Sample I Sample I1 Uhloral hydrate 60 pg/CC 51Opg/cc Trichloroacetic acid 22.5 15 Urocihloralic acid (calcu-44 35 lated as chloral hydrate) Urine : Chloral hydrate and trichloroacetic acid Blood : Trichlor.oethano1, 25 p g ; trichloroacetic negative ; urochloralic acid : 560 pg/cc. acid, 32.5 p g ; chloral hydrate, 32.5 pg/cc.watery fluid containing urochloralic acid only.Summary. The results indicate that in the early stage of pregnancy chloral hydrate and its metabolites pass from the blood into the amniotic fluid. However, urochloralic acid, which is the form by which chloral hydrate is excreted by the kidneys, was found also at a stage when the gestation had progressed to two-fifths. In later pregnancy only urochloralic acid was found, which indicates that in the later stages the amniotic fluid contains essentially the products of foetal renal excretion. In view of the small quantities of amniotic Auid collectable in the third rabbit, the potential error in the figures given is considered to be large, and the results should be evaluated 1. Guerov, L., Arch. f. Gyn., 1872, v3, 241. 2. G~,~~~~~, L., in ~~~d b~ J,@sePh: Chemical ~m~r y o~o g y , Cambridge University press, 1931.3. Schroeder, R., Arch. f. Gyn., 1891, v39, 306. rather as qualitative than quantitative, It seems that at the time of gestation of the third rabbit, kidney function has set in and the transudative portion, containing the compounds circulating in the blood, is already mixed with urochloralic acid of urinary origin. At a later stage the urinary liquid replaces the reabsorbed transudate leading to a more . .. . 4.Plentl, Albel;t A., and Donald L. Hutchinson: Paper presented a t the 39th ICliniml Congress, Am.

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