The role of tyrosine phosphorylation in the regulation of tyrosine protein kinase activity was investigated using site‐directed mutagenesis to alter the structure and environment of the three tyrosine residues present in the C terminus of avian pp60c‐src. Mutations that change Tyr 527 to Phe or Ser activate in vivo tyrosine protein kinase activity and induce cellular transformation of chicken cells in culture. In contrast, alterations of tyrosine residues present at positions 511 or 519 in c‐src do not induce transformation or in vivo tyrosine protein kinase activity. Amber mutations, which alter the structure of the pp60c‐src C terminus by inducing premature termination of the c‐src protein at either residue 518 or 523 also induce morphological transformation and increase in vivo tyrosine phosphorylation, whereas removal of the last four residues of c‐src by chain termination at residue 530 does not alter the kinase activity or the biological activity of the resultant c‐src protein. We conclude from these studies that C‐terminal alterations which either remove or replace Tyr 527 serve to activate the c‐src protein resulting in cellular transformation and increased in vivo tyrosine protein kinase activity.

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In this report the in vitro and in vivo pharmacological and pharmacokinetic profile of (Ϫ)-(S)-N-(␣-ethylbenzyl)-3-(carboxymethoxy)-2-phenylquinoline-4-carboxamide (SB 235375), a low central nervous system (CNS)-penetrant, human neurokinin-3 (NK-3) receptor (hNK-3R) antagonist, is described. SB 235375 inhibited 125 I- [MePhe 7 ]-neurokinin B (NKB) binding to membranes of Chinese hamster ovary (CHO) cells expressing the hNK-3R (CHO-hNK-3R) with a K i ϭ 2.2 nM and antagonized competitively NKB-induced Ca 2ϩ mobilization in human embryonic kidney (HEK) 293 cells expressing the hNK-3R (HEK 293-hNK-3R) with a K b ϭ 12 nM. SB 235375 antagonized senktide (NK-3R)-induced contractions in rabbit isolated iris sphincter (pA 2 ϭ 8.1) and guinea pig ileal circular smooth muscles (pA 2 ϭ 8.3). SB 235375 was selective for the hNK-3R compared with hNK-1 (K i Ͼ 100,000 nM) and hNK-2 receptors (K i ϭ 209 nM), and was without effect, at 1 M, in 68 other receptor, enzyme, and ion channel assays. Intravenous SB 235375 produced a dose-related inhibition of miosis induced by i.v. senktide in the rabbit (ED 50 of 0.56 mg/kg). Intraperitoneal SB 235375 (10 -30 mg/kg) inhibited citric acid-induced cough and airways hyper-reactivity in guinea pigs. In mice oral SB 235375 (3-30 mg/kg) was without significant effect on the behavioral responses induced by intracerebral ventricular administration of senktide. Pharmacokinetic evaluation in the mouse and rat revealed that oral SB 235375 was well absorbed systemically but did not effectively cross the blood-brain barrier. The preclinical profile of SB 235375, encompassing high affinity, selectivity, oral activity, and low CNS penetration, suggests that it is an appropriate tool compound to define the pathophysiological roles of the NK-3Rs in the peripheral nervous system.

SUMMARYWe have characterized a set of 15 monoclonal antibodies to pl9gag, one of the internal proteins of avian sarcoma and leukaemia viruses. All the antibodies work in immune precipitations as well as in immunoblotting, though with different efficiencies. We have developed a simple epitope mapping technique, which uses partial chemical cleavages at methionine or tryptophan residues followed by immunoblotting from SDS-polyacrylamide gels, to localize the epitopes of nine of these antibodies. The epitopes fall into at least four classes. The mapping procedure should also be useful for other antigens of known primary structure.