The interaction of the synthetic serum thymic factor (FTS, "facteur thymique serique") with human T lymphocytes from two established T The thymus gland has been shown to produce a number of factors or "hormones" that promote the differentiation of thymus-derived cells (T cells) and induce the appearance of their specific markers. We showed in 1971 that thymic extracts induce the appearance of the best-characterized of these markers, the 0 (Thy-i) antigen, on 0-negative bone marrow rosette-forming cells (1). It was ultimately demonstrated that there exists in normal serum an active principle with activity on rosette-forming cells identical to that of thymic extracts. The absence of this principle in serum from thymectomized or nude (athymic) mice demonstrated the strict thymic dependence of this factor (2).The molecule responsible for this activity has been isolated from pig serum and called "facteur thymique senique" (FTS). FTS is a nonapeptide whose amino acid sequence has been determined. FTS has been synthesized, and the synthetic material shows full biological activity and displays chromatographical characteristics identical to those of biological FTS in several chromatography systems (3, 4).The recent observation of the localization of antibodies directed against synthetic FTS on the thymic epithelium has provided direct demonstration of its thymic origin.tThe binding to specific receptors on its target cell is the first step in the action of a polypeptide hormone. It is thus of utmost importance for the understanding of the cellular mode of action of FTS to search for and characterize FTS receptors on lymphoid cells. With this in view, we have applied the methodology now well established for polypeptide hormones (5). This effort was significantly helped by the finding of two lymphoblastoid cell lines that showed high levels of FTS binding. MATERIALS AND METHODSLymphoblastoid Cell Lines. The initial lymphoblastoid T cell line (1301) was given by S. M. Fu and M. Fellous. It was derived from a leukocyte culture of a patient with acute lymphoblastic leukemia. Lymphocytes were maintained at 370C in RPMI 1640 essential medium, supplemented with 10% fetal calf serum, 1% glutamine, antibiotics and, Fungizone. The cells were used in the binding studies when they were in the stationary phase of growth. Their viability was determined by their capacity to exclude trypan blue dye. The T cell nature of the cell line was established by the study of its markers (6, 7). Results of these studies are presented in Table 1. Methods used for marker evaluation have been previously reported (6, 7). Other cell lines were also studied in less detail. The origin, nature and characteristics of these various cell lines are presented in Table 1.FiTS. Labeled [3H]FTS was prepared according to a method consisting of lysine methylation by use of 3H-labeled sodium borohydride and formaldehyde (8). Briefly, 1 mg of synthetic FTS (Choay, Paris, France) was incubated for 1 hr at 40C with 100 mCi of NaB3H4 and 1 mmol of formaldehyde...

SUMMARYThis article describes the radiosynthesis of "C-labelled S-adenosylmethionine by an enzymatic process. This methyl donor was prepared by condensation of L-(methyl-"C) methionine with ATP. The synthesis and purification could be carried out in 20 minutes with a final yield of 80 %. The specific radioactivity obtained was close to 200 Ci/mmole. 6 mCi of 'lc-labelled S-adenosylmethionine was injected in a rabbit, and its repartition followed by an opticamera.

S u m m a r yT h e s y n t h e s i s of the t r i c h l o r o m e t h y l a n a l o g u e of be n z y I ox y c ar b o n y 1 -t h r e o n i n e 1' hi s precursor was isomer. They were separated by HPLC using a chiral stationnary phase. They have a molar specific activity of 3190 GBq/mmol, 86 Ci/mmol.i s d e s c r i bed .reduced by tritium gas to give [methyl-3 H3]-threonine and its all0Key words : selective CrO3 oxidation, 3II-labelling, trichloromethylation, trichlorinated 2-threonine. I n t r o d u c t i o nBiological investigations with peptides and proteins frequently require radio-labelled compounds with high specific activities.IIuman insulin differs from porcin insulin by only one aminoacid content : threonine replaces alanine at the C-terminal position of the a-chain. We develop an original procedure for labelling the human insulin, which consists of substituing the alanine of the porcine insulin with labelled threonine by the aid of carboxypeptidase.Catalytic reduction of halogenated or unsaturated precursor by tritium gas is t h e most convenient way of labelling organic compounds. So we focused our attention on the synthesis of the trichlorinated analogue 1 of Z-threonine. The benzyloxycarbonyl group was chosen as the masking agent of the amino function because of its lability under reductive conditions : the labelling step could directly lead to the free amino-acid. A high specific activity could be expected from the tritiation of the poly-halogenated group.

Biosynthesis of the C‐terminal carboxamide group of peptide hormones was studied using comparatively pGlu‐His‐Pro‐Gly and Glu‐His‐Pro‐Gly‐Lys‐Arg as putative precursors of the tripeptide, thyroliberin (TRH). Rat hypothalamus granules were found to contain an amide group forming activity which converts both peptide substrates into TRH. Comparison of the rate of conversion of the two substrates indicated that the C‐terminal dibasic extension favored a 10‐fold increase in the production of amidated peptide. It is suggested that this type of structure may be present in the putative biosynthetic precursor of TRH and that it may provide a better substrate for the enzyme(s) involved in C‐terminal amidation.

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