ABSTRACr Rat ,-lipotropin was isolated from 40 anterior pituitaries using high efficiency chromatography columns and sensitive fluorometric methods. The P-lipotropin was characterized as to molecular weight, amino acid composition, and generation of opioid activity by trypsinization. Other opioid peptides, as well as a precursor to opioid peptides with a molecular weight larger than that of P-lipotropin, were observed in this tissue. The series of peptides a-, fi-, and y-endorphin and methio- An automatic fluorescence detection system was used for column monitoring of peptides (9). In this system a discontinuous sampling valve allowed typically 2-10% of the column effluent to react with fluorescamine, while the remainder was directed to a fraction collector. An LKB (Hicksville, NY) gradient mixer, a Milton Roy (Riviera Beach, FL) minipump, and an Altex Scientific (Berkeley, CA) 7000 lbs./inch2 sample injection valve were the major components of the chromatography system. Aliquots of the collected fractions were hydrolyzed in constant boiling hydrochloric acid that had been redistilled over sodium dichromate (12). Thioglycolic acid (0.1% vol/vol) was added to prevent oxidation of cysteine (13). Amino acid analyses were performed on an instrument that used fluorescamine for detection at the picomole level as previously reported (10). Trypsin (twice crystallized) was obtained from Sigma (St. Louis, MO). Bioassay of opioid activity was carried out with neuroblastoma X glioma hybrid cells (NG 108CC15) (14), which were generously provided by M. Nirenberg, National Institutes of Health, Bethesda, MD. Opioid activity was measured by competitive binding with [3H]Leu-enkephalin (Amersham/Searle) to these cells, and activity is reported in terms of Leu-enkephalin equivalents. Details of the binding assay will be published elsewhere. Other experimental details are given in the figure legends and in Results.
RESULTSAnterior pituitaries from 40 rats were extracted with acid/ acetone according to the procedure of Li et al. (15), with some modifications. The tissue was homogenized in 2.5 ml of cold 75% acetone/25% 0.2 M hydrochloric acid containing 0.01% thiodiglycol and 0.001% phenylmethylsulfonyl fluoride (a protease inhibitor). The following steps were performed at room temperature. Acetone was removed under a stream of nitrogen and the volume was brought to 2 ml by the addition of water. Lipids were extracted with three 1-ml portions of ethyl acetate/ether (3:1 vol/vol). The aqueous phase was fractionated on a Sephadex G-75 column and the effluent was monitored for fl-lipotropin by the following procedure. Aliquots (25 Ml) from each collected fraction were dried and then incubated with 10 Mg of trypsin in 50 ,l of 0.05 M Tris buffer (pH 8.5) at 370 for 18 hr. Opioid activity was then determined by the competitive binding assay. A minor peak of activity was found in the 30,000-to 60,000-dalton range (fractions 20-25) while the major activity was found in fractions 34-37, which corresponded to the sheep 03-lipotropin standard...