Radioiodination of the stable metabolic fragment of bradykinin, RPPGF

Arg-Pro-Pro-Gly-Phe (RPPGF, BK[1-5]), is a stable metabolite of the peptide hormone bradykinin. Considering the short half-life of bradykinin (BK, approximately 15 secs), RPPGF has been used as a marker for BK's endogenous generation. A lack of a radioiodinated RPPGF has precluded the development of a radioimmunoassay for this peptide. The present study describes a two-step reaction that allows for the incorporation of 125I into the aromatic ring of the phenylalanine of RPPGF. This radioiodinated analog is recognized by an antibody to RPPGF, demonstrating its utility for the development of a radioimmunoassay for measurements of RPPGF, a stable metabolic product of bradykinin.

New photoaffinity labelled agonists of bradykinin

Several photoaffinity labelled agonists of the peptide hormone bradykinin (BK) were synthesized by solid phase methods. Their biological activities and binding affinities were determined in both the isolated rat uterus (RUT) and guinea pig ileum (GPI). As photoreactive groups p-benzoyl-phenylalanine (Bpa) and the arylazides azidobenzoic acid (ABA) and azidosalicylic acid (ASA) were attached to the N-terminus of the BK agonists. In addition, Bpa was incorporated at different positions of the BK sequence. Three different types of BK agonists were used. Firstly, the photolabels ASA and ABA were attached to BK or to Lys-BK (kallidin). Secondly, tyrosine containing BK analogues, suitable for radioiodination, were labelled. This series is derived from the naturally occurring analogue phyllokinin [BK-Ile-Tyr(SO3H)] and from BK analogues with tyrosine at position 0 and 3. The third series includes several analogues with D-N-methyl-phenylalanine (D-NMe-Phe) at position 7, which selectively discriminate between the RUT and GPI bradykinin B2 receptors. Among the photoaffinity labelled BK agonists, the iodinatable Lys(ASA)-BK (50.8% on RUT, 73.0% on GPI), ASA-BK (26.3% on RUT), Bpa-BK-Ile-Tyr (13.6% on RUT, 14.0% on GPI) and the iodinated [D-Bpa-1, 3-I-Tyr0]-BK (15.5% on RUT, 19.0% on GPI) retained a relatively high biological activity compared with BK (100%). Thus, although BK agonists are known to allow only very restricted modifications without a strong reduction in biological activity, these compounds should be useful candidates for receptor labelling.

Apparent molecular weight of substance P/neurokinin-1 receptors determined using a photoaffinity labelled probe, [(3'-125I) D-Tyro, (4'-N3)Phe8, Nle11]-substance P

A photoreactive derivative, [(3'-125I) D-Tyro, (4'-N3)Phe8, Nle11]-substance P (SP) was prepared and iodinated using carrier-free [125I] to determine the apparent molecular weight of one sub-type of neurokinin (NK) receptor, the SP/NK-1 type. The unlabelled analogue competed for [3H]-SP sites with an IC50 of 10 nM. The radioactive photoprobe (KD approximately 0.17 nM, Bmax = 15.6 fmol/mg protein) was used to photoaffinity label membranes prepared from rat brain. Autoradiographs revealed that a single band with an apparent molecular weight of 46,000 daltons was specifically labelled. This labelling was inhibited by non-radioactive SP in a concentration-dependent manner (1.0 nM-0.1 mM) suggesting that the observed labelling represents the SP/NK-1 receptor type.

Synthesis of new head-activator analogues and their application for improved radioimmunoassays

New analogues of head activator were produced for receptor and radioimmunoassay studies. The precursor molecules [(4'-I)Phe11] head activator and [Tyr11] head activator were synthesised for catalytic tritiation and iodination, respectively. With the tracer [(3,5-125 I2)Tyr11] head activator the sensitivity range of the radioimmunoassay was 5-100 fmol.

A new method of iodine labelling of peptide hormones

Usually peptide hormones and related compounds are radioactively labelled with iodine on tyrosine residues of the peptide. However many peptide hormones do not contain tyrosine or the iodinated tyrosine interferes with the biological properties. In order to circumvent these and other problems, a general method is proposed which allows the introduction of iodine into the para-position of phenylalanine with a modified Sandmeyer procedure. This last-step modification together with HPLC purification permits the obtention of carrier-free and metabolically stable labelled products with maximal specific activity possible. The model has been carried out on several peptide-models like angiotensin II, endorphine and head activator peptide.

Oligopeptides that specifically inhibit membrane fusion by paramyxoviruses: studies on the site of action

Previous studies from this laboratory showed that oligopeptides with amino acid sequences similar to the sequence of the N-terminal region of the F1 polypeptide of paramyxoviruses inhibited the membrane fusing activity of the F protein, and thereby inhibited virus infectivity at the level of penetration and virus-induced cell fusion and hemolysis. The site of action of these oligopeptide inhibitors has been investigated. Radioactively labeled oligopeptides were found to bind to cells, but not to virus. Pretreatment of cells, but not virus, at 4 degrees with oligopeptides inhibited the initiation of infection and hemolysis induced by measles virus. The binding of the oligopeptides to cells was reversible at 25 or 37 degrees. Oligopeptides were synthesized with a chloromethylketone group to enable them to bind irreversibly, or with an azido group to permit them to be cross-linked in situ by photoactivation. The results with these derivatized oligopeptides, which retained their inhibitory activity, confirmed that they bind to, and express their inhibitory activity on, cells and not virus. The results suggest that the oligopeptides react with receptor sites on the cell membrane and inhibit membrane-fusing activity by competing with the F1 polypeptide for such sites. A Scatchard analysis of the binding of an oligopeptide to CV-1 cells revealed that it bound with a dissociation constant of 1.2 X 10(-7) M and that there were approximately 3.0 X 10(6) binding sites per cell.