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Sheep β-lipotropic hormone (β-LPH) contains within its structure the complete amino acid sequence of γ-LPH. These two molecules have a sequence of amino acid entirely similar to βSer-melanophore-stimulating hormone (MSH). We have shown that β-LPH is not likely to be degraded into γ-LPH and β-MSH during the purification procedure, or by incubation in an acetic acid/acetone mixture at 50 °C for 20 min. Results are compatible with the hypothesis that β-LPH could be the biological precursor of β-MSH and that γ-LPH is an intermediate component.

The far ultraviolet circular dichroism spectra of sheep beta-lipotropic hormone (beta-LPH) were recorded under different conditions of pH, temperature, salt concentration, and solvent composition. Results confirm the stability of the hormone in strong basic or acidic solutions; moreover, temperatures up to 50 degrees C do not seem to affect noticeably the conformation of beta-LPH. However, increasing the NaC1 concentration or addition of dioxane in the solution brings about a conformational transition of the chain, interpreted as an increase in the helical content. The method of Yang (Chen, Y.H., Yang, J. T. & Martinez, H. M. (1972) Biochemistry 11, 4120-4131) was used to compute the proportion of helical, beta, and unordered forms of the hormone chain. The proportions are compared with those obtained from Fasman's predictive method (Chou, P. Y & Fasman, G. D. (1974) Biochemistry 13, 211-221 and Chou, P. Y. & Fasman, G. D. (1974) Biochemistry 13, 222-245) based on the known amino acid sequence of beta-LPH.

Sheep gamma-lipotropic hormone (gamma-LPH) is a pituitary polypeptide made of 58 amino acids and is formed of the first 58 residues of beta-lipotropic hormone (beta-LPH). The C-terminal portion (41-58) of gamma-LPH is identical with the structure of beta-melanophore-stimulating hormone (beta-MSH). We hypothetized in 1967 that beta-LPH could be the biological precursor of beta-MSH and that gamma-LPH could be an intermediate compound. We demonstrated in 1974 that beta-LPH is actively synthesized in the bovine pituitaries. We now studied the biosynthesis of gamma-LPH by monitoring the incorporation of radioactive amino acids in beef pituitary slices. We separated gamma-LPH from the other radioactive proteins with a method previously described. We characterized the radioactive proteins by ion-exchange chromatography, gel filtration and polyacrylamide gel electrophoresis. Our results show that radioactive gamma-LPH was actively synthesized. This gamma-LPH has all the chemical characteristics of nonradioactive gamma-LPH. However, in the conditions used, we were unable to demonstrate biosynthesis of beta-MSH. These results suggest that gamma-LPH is biosynthesized more slowly than beta-LPH and that the conversion into beta-MSH, if it exists, is a slow or subactive process in the species studied.

R e~u le 19 juillet %9732Bertagna, X., Lis, M., Gilardeau, 6 . & GhrCtien, M. (1974) BiosyntNse "hz Vitro9' de 1'Hormone BCta-Lipstropique de Boeuf. Cart. J. Binchem. 52,[349][350][351][352][353][354][355][356][357][358] L'hormone bCta-lipotropique (p-LPH) est une protiine hypophysaire constitube dd'une seule chaiine de 90 acides aminks et possbdant une portion de sdquence (41-58) reproduisant exxtement celle de 19hormone mClano-stimulante beta (8-MSH). Dans I'hypoehme selon Haquelle la B-LPH serait le prdcurseur de la 8-MSH nous awns CtudiC, par des mithodes d'incubation in vitro de tranches d'hypsphyses de bmuf en presence d'acides aminCs rnarqub, la bio-synth6se de ces deux protkines. Griice i une modification apportde h la mCthode d'extraction standard de la pLPH nous Ctions en mesure de caractkriser ces deux molCcules par leur cornportement sur 1es khangeurs d'ions, tamis moldculaires et Clectrophor&se sur geH de polyacrylamide. Les rCsultats prCsentCs rnontrent que les tranches d'hypophyses incorporent les acides aminks marquCs dans un matCriel indistinguible de la PLPH dans ces trois systkmes alors qu'aucune biosynthbe de 8-MSH n'est obtenue dans les wCmes conditions aprks 4 h d'incubation. Ces faits sugghent que la conversion de p-LPH en p-MSH, si elle existe, est un phdnornkne lent ou p u actif dont la ddmonstration reste h faire dam des incubations plus prolongdes.Bertagna, X., Lis, M., Gilardeau, C. & ChrCtien, M. (1974) Biosynthbe "In Vitrs" de 1'Hormone Beta-Lipotropique de Boeuf. Can. J. Bischem. 52,[349][350][351][352][353][354][355][356][357][358] Sheep beta-lipotropic hormone (p-LPH) is a pituitary hormone made of 90 amino acids and having a portion of its sequence (41-58) identical with the structure of beta-melanocytestimulating hormone (p-MSH). We hypothetized that &LPH could be the biological precursor of p-MSH. We studied the biosynthesis of these two molecules by monitoring the incorporation of radioactive amino acids in beef pituitary slices. We separated p-LPH from the other radioactive proteins with the usual method of purification described previously and we characterized the proteins by ion-exchange chromatography, gel filtration, and po%yacrylamide gel electrophoresis. Bur results show that the pituitary slices synthesized a radioactive @-LPH which has all the characteristics of won-radioactive B-LPH. However, in the conditions used, we could not demonstrate any biosynthesis of 0-MSM after 4 h incubation. These results suggest that the conversion of B-LPH into p-MSH, if it exists, is a slow process and should be studied in more prolonged incubations.