Important role of peptide leukotrienes (p-LTs) in the resting tonus of isolated human bronchi

The quality of the resting tonus in isolated human bronchi was investigated using a peptide leukotriene (p-LT) antagonist, a 5-lipoxygenase inhibitor and others. (E)-2,2-Diethyl-3'-[2-[2-(4-isopropyl)-thiazoyl]ethenyl]succina nilic acid sodium salt (MCI-826), a newly synthesized compound that is a highly selective antagonist to LTD4 and LTE4, markedly relaxed the isolated human bronchi at low concentrations. A selective and competitive arachidonate 5-lipoxygenase inhibitor, 2,3,5-trimethyl-6-(12-hydroxy-5,10-dodecadiynyl)-1,4-benzoquinone (AA-861), also potently lowered the tonus. In addition, a large amount of spontaneously formed p-LTs was detected in the isolated human bronchial tissue as well as the lung parenchymal tissue. The isolated human bronchi responded to indomethacin treatment with contractions and the acceleration of p-LT formation. Atropine, an anticholinergic; mepyramine, an antihistaminic; and OKY-046, a thromboxane synthetase inhibitor, all showed no effect on the resting tonus. Taking into consideration the high responsiveness of the human airway smooth muscle to p-LTs and the present results, which were different from those on isolated guinea pig tracheas, it is strongly suggested that the spontaneously formed p-LTs largely participate in the resting tonus of the majority of isolated human bronchi.

Effects of rokitamycin on bilirubin-albumin binding: a study in vitro

The effects of rokitamycin, a macrolide antibiotic, on the binding of bilirubin to albumin were examined in vitro using blood plasma from young rats with hyperbilirubinemia, bilirubin-supplemented serum separated from human cord blood, and the human serum from a newborn infant with icterus gravis neonatorum. Rokitamycin at concentrations from 1 to 500 micrograms/ml (the entire range over which experiments could be conducted) had little or no effect on the concentration of unbound bilirubin in any of the incubation mixtures used. This result suggests that rokitamycin has no effect on the binding of bilirubin to albumin.

Crystal structures of Boc-D- and L-Iva-L-Pro-OBzl: unturned conformation of Aib-Pro sequence unaffected by replacement of Me with Et in Aib

The crystal structures of the isovaline (Iva) containing dipeptides, Boc-D-Iva-L-Pro-OBzl and Boc-L-Iva-L-Pro-OBzl, were determined by x-ray diffraction. The diastereomeric peptides were shown to adopt unturned conformations closely similar to each other (phi Iva 52 degrees, psi Iva 46 degrees, phi Pro -65 degrees, and psi Pro 143 degrees for D-Iva-L-Pro sequence and phi Iva 52 degrees, psi Iva 44 degrees, phi Pro -63 degrees, and psi Pro 148 degrees for L-Iva-L-Pro sequence). The Pro ring of each peptide was in C gamma-endo conformation. The unusually large angle CIva-NPro-C delta Pro values (131 degrees in both peptides) were observed, that was due to steric repulsion between the delta-methylene of Pro and the alkyl side chain of Iva residue. These conformations were essentially the same as that of the corresponding alpha-aminoisobutyric acid (Aib)-containing peptide Boc-Aib-L-Pro-OBzl. The result has demonstrated that replacement of either one of the two methyl groups of the Aib residue in Boc-Aib-L-Pro-OBzl with an ethyl group does not cause any significant change in the unturned conformation of the dipeptide.

The lectin concanavalin A stimulates a protein-tyrosine kinase p72syk in peripheral blood lymphocytes

We report that the activation of porcine peripheral blood lymphocytes (PBL) by lectin concanavalin A (Con A) led to the increase in tyrosine phosphorylation on 84-, 72-, 55-, 40-, and 33-kDa proteins. A non-receptor protein-tyrosine kinase (PTK), p72syk (Taniguchi et al. (1991) J. Biol. Chem. 266, 15790-15796), was detected in PBL around 0.1% of total protein and distributed in both particulate and cytosolic fractions. Furthermore, Con A induced a rapid activation of p72syk within 1 min in a manner similar to the time course of Con A-induced protein-tyrosine phosphorylation. These results suggest that p72syk plays a certain role in the activation of PBL and that p72syk may be one of the major non-receptor PTKs in T cells as well as in B cells.

Differences in the effects of treatment of uncompacted and compacted mouse embryos with phorbol esters on pre- and postimplantation development

Differences are described in the effects of treatment of preimplantation mouse embryos with low levels (0.01-1 nM) of phorbol myristate acetate (PMA), during three different periods of a 48-h culture from the 2-cell stage, on pre- and postimplantation development. Treatment of embryos with PMA for 48 h (first group) or 24 h (second group) from the 2-cell stage caused premature cavitation (prior to the 16-cell stage) and it also reduced the size and alkaline phosphatase (ALPase) activity of inner cell masses (ICMs), as well as the numbers of cells in blastocysts, in a dose-dependent manner. Treatment of early morulae with PMA for 24 h (third group) did not have the above mentioned effects on embryos but inhibited the formation and subsequent enlargement of the blastocoel. The blastocysts that were allowed to develop in the three treatment groups were examined for postimplantation development. Implantation was unaffected in all groups. The survival rate after implantation was low in the first and second groups but relatively high in the third group. The results indicate that an embryo exposed to PMA for 24 h from the 2-cell stage forms a premature blastocoel, and, in such an embryo, quantitative and qualitative differentiation into the ICM is blocked but qualitative differentiation into trophectoderm is uninhibited. Consequently, the embryo can implant but does not survive for a long time. When embryos were exposed to PMA for 24 h from the early morula stage, the formation and enlargement of the blastocoel were inhibited even though the treatment had a minimal effect on other developmental events.(ABSTRACT TRUNCATED AT 250 WORDS)

[Evaluation of pipecuronium bromide during halothane or enflurane anesthesia--a comparison with pancuronium regarding the optimal dose and the effect of volatile anesthetics on neuromuscular blockade]

Pipecuronium, a new muscle relaxant, was examined in surgical patients in a multi-center cooperative study. Neuromuscular blocking action, circulatory effect and side effects of pipecuronium were investigated in comparison with those of pancuronium bromide. Mechanical twitch responses of adductor pollicis muscle evoked by supramaximal stimulation of the ulnar nerve every ten seconds were recorded. The following results were obtained. 1. Approximately 100% twitch depression was obtained after the administration of pipecuronium 0.04 mg.kg-1. 2. Enflurane and halothane did not influence the onset time and recovery time. But enflurane showed more prolonging effect on the duration of pipecuronium induced block than halothane. 3. No clinically significant changes in heart rate and blood pressure were observed. It was concluded that the minimum of 0.04 mg.kg-1 of pipecuronium is necessary for an initial dose and the maintenance dose of pipecuronium can be reduced under enflurane anesthesia.

Dimaprit, a histamine H2-agonist, inhibits anaphylactic histamine release from mast cells and the decreased release is restored by thioperamide (H3-antagonist), but not by cimetidine (H2-antagonist)

Whether anaphylactic histamine release from rat peritoneal mast cells is influenced by betahistine, a histamine H1-receptor agonist/H3-antagonist, and dimaprit, an H2-agonist, was examined. Treatment with dimaprit at 6 and 60 microM for 20 min significantly inhibited the anaphylactic histamine release, whereas betahistine at up to 80 microM under the same conditions did not affect it. Treatment with dimaprit at 6 and 60 microM for 1 to 20 min and for 5 to 20 min, respectively, caused a time-dependent inhibition of the release, but up to 30 min treatment with 8 and 80 microM betahistine had no effect. The decreased histamine release induced by dimaprit was recovered by neither mepyramine nor cimetidine. However, thioperamide, an H3-selective antagonist, dose-dependently restored the diminished release. From these results, the inhibition of anaphylactic histamine release by dimaprit is not produced by the stimulation of H2-receptors, but involves the stimulation of H3-like receptors or H3-subtype receptors, which are distinct from the H3-receptors located in brain, and suggests that the receptor plays an important role in the negative feedback regulation of histamine release.

Phosphorylation sites of myelin basic protein by a catalytic fragment of non-receptor type protein-tyrosine kinase p72syk and comparison with those by insulin receptor kinase

Myelin basic protein has been used as a model substrate for determination of substrate recognition motif of various protein kinases. In this report phosphorylated sites of bovine brain myelin basic protein were studied with a catalytic fragment of protein-tyrosine kinase p72syk. Three of four tyrosine residues in myelin basic protein were phosphorylated by this kinase. Major phosphorylated site was 134Y and minor phosphorylated sites were 68Y and 127Y. As the phosphorylation site by p56lck was only 68Y, the recognition motif of p72syk was quite different from that of p56lck. Furthermore, the fact that elution pattern on HPLC of the phosphopeptides obtained by insulin receptor kinase was different from that by p72syk suggested that the recognition motif of p72syk was also different from that of insulin receptor kinase. These results may suggest that each protein-tyrosine kinase has a specific substrate recognition motif.

Association with B-cell-antigen receptor with protein-tyrosine kinase p72syk and activation by engagement of membrane IgM

We have demonstrated that a 72-kDa non-receptor-type protein-tyrosine kinase (p72syk) was co-immunoprecipitated with membrane IgM in digitonin lysates of porcine tonsillar cells and was rapidly activated following the engagement of membrane IgM. This activation was occurred within 5 s, even in the presence of EGTA and 5,5'-dimethyl-bis-(O-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid as extracellular and intracellular Ca(2+)-chelating agents, respectively, as well as in the presence of the protein-kinase-C inhibitor, H-7. Additionally, genistein, a potent protein-tyrosine kinase inhibitor, was capable of reducing both IgM-stimulated Ca2+ mobilization and p72syk activation in a dose-dependent manner. These results indicate that p72syk is physically associated with the B-cell-antigen receptor, participating in antigen-mediated signal transduction in both a Ca(2+)-independent and protein-kinase-C-independent manners.

Involvement of protein kinase C in nuclear migration during compaction and the mechanism of the migration: analyses in two-cell mouse embryos

Compaction and nuclear migration occur in mouse embryos at the late eight-cell stage. It has been reported that activators of protein kinase C (PKC) increase adhesion of cells at the two-cell, four-cell, and uncompacted eight-cell stage. We report here that nuclear migration followed the increased adhesion of cells in such embryos when they were treated with PKC activators. These cellular events resembled those in normal embryos at the late eight-cell stage and were blocked by sphingosine, a PKC inhibitor. The responses were proportional to the dose of the PKC activator. Molecular analogues of the PKC activators, which do not affect PKC, did not induce these events. These results suggest an important role for PKC in initiation of nuclear migration as well as in compaction. Experiments were also conducted to identify the source of the mechanical force that moves the nucleus. Nuclear migration was suppressed in embryos pretreated with colchicine. Calmodulin is known to have effects on Ca(2+)-induced assembly and disassembly of microtubules. The calmodulin antagonists W-7 and W-5 suppressed nuclear migration. These results suggest that microtubules are essential for the migration and that nuclei are migrated via the Ca(2+)-induced, calmodulin-mediated assembly and disassembly of the microtubule networks. Together, these results obtained with PKC activators/inhibitor, colchicine, and calmodulin antagonists suggest that nuclear migration is mediated by increases in PKC activity, requires intact microtubules, and is accompanied by PKC-dependent increases in cell-cell adhesion.

Cerebellar hypoplasia in the hyperbilirubinemic Gunn rat: morphological aspects

Gunn rats, a mutant strain of rats, suffer from autosomal recessive hyperbilirubinemia. The homozygotes (j/j) develop jaundice soon after birth and often exhibit kernicterus and cerebellar hypoplasia that are due to bilirubin. Therefore, j/j Gunn rats have been used as an animal model of bilirubin encephalopathy, as well as of neonatal hyperbilirubinemia. In this review, we discuss morphological aspects of the cerebellar hypoplasia that is due to bilirubin and describe the relationship between plasma bilirubin levels and cerebellar hypoplasia, as well as the pathogenesis of cerebellar hypoplasia, including abnormal histogenesis of the cerebellar cortex, abnormalities associated with Purkinje cells and abnormal synaptogenesis in j/j Gunn rats.

Protein-tyrosine kinase p72syk is activated by thrombin and is negatively regulated through Ca2+ mobilization in platelets

Activation of platelets by thrombin results in a dramatic increase in tyrosine phosphorylation on multiple cellular proteins (Ferrell, J. E., and Martin, G. S. (1988) Mol. Cell. Biol. 8, 3603-3610; Golden, A., and Brugge, J. S. (1989) Proc. Natl. Acad. Sci. U. S. A. 86, 901-905; Nakamura, S., and Yamamura, H. (1989) J. Biol. Chem. 264, 7089-7091). However, none of the responsible protein-tyrosine kinase has been reported so far. We report here that p72syk, one of the non-receptor-type protein-tyrosine kinases, is activated following thrombin stimulation in blood platelets. Washed porcine platelets were stimulated by thrombin, and the activation of p72syk was assessed in an immunoprecipitation kinase assay. The activity of p72syk increased within 5 s, reached a maximum at 10 s, and decreased to a basal level within 60 s after 0.5 unit/ml thrombin stimulation. The amount of immunoprecipitated p72syk was not altered throughout the time course. This activation was greatly enhanced in a dose-dependent manner and was completely canceled by the pretreatment of platelet suspension with hirudin, a specific antagonist of thrombin. In the Ca(2+)-depleted condition both extra- and intracellularly, the activation of p72syk was still persistent; in contrast, the deactivation process was completely abrogated even at 120 s after thrombin stimulation. In addition, the replenishment of Ca2+ resulted in a similar deactivation pattern as seen in the Ca(2+)-rich condition. Furthermore, this deactivation was also canceled by the pretreatment of platelets with W7, a calmodulin antagonist, as well as ML9, a myosin-light-chain kinase inhibitor. These results indicate that p72syk can be a responsible enzyme to the protein-tyrosine phosphorylation events following the platelet activation by thrombin and may be negatively regulated by Ca2+ in a calmodulin-dependent manner, inter alia myosin light-chain kinase, in thrombin-stimulated platelets.

Developmental alteration of serotonin neurons in the raphe nucleus of rats with methylazoxymethanol-induced microcephaly

Prenatal exposure of pregnant rats to methylazoxymethanol acetate (MAM), an anti-mitotic agent, on day 15 of gestation induces severe microcephaly in the offspring. The present study first investigated a developmental alteration of serotonin (5HT) neurons immunohistochemically in the dorsal and median raphe nuclei in serial sections in both control and microcephalic rats (MAM-rats) at 35 days of age. 5HT-immunoreactive neurons in the MAM-rats were reduced in number and irregularly distributed in the dorsal and median raphe nuclei compared with those in the control. The dendrites of neurons in these nuclei in the MAM-rats were very short and twisted. A follow-up observation on the development of the cerebral cortex at 5, 9 and 28 days of age was performed using Nissl-stained preparations, which revealed a disorganized cell arrangement in the cerebral cortex of the MAM-rats at the very early postnatal period. Furthermore, the distribution of 5HT-immunoreactive fibers into the cerebral cortex was also examined using brains of 28 days of age. In MAM-rats of this age, abnormally tortuous 5HT-immunoreactive fibers were observed in the cerebral cortex. 5HT neurons in the raphe nuclei are known to project their ascending axons widely into the entire cortical area during the 1st postnatal week. Thus, the association of disorganized cortical cell arrangement and the hyperdense and tortuous distribution of 5HT-immunoreactive fibers in the cerebral cortex support the idea of target-dependent secondary degeneration of 5HT neurons in the dorsal and median raphe nuclei of the MAM-rats.

Inhibitory effect of mitoxantrone on activity of protein kinase C and growth of HL60 cells

Mitoxantrone, a new anthraquinone, showed inhibitory an effect on protein kinase C (PKC) activity. Its IC50 value was 4.4 micrograms/ml (8.5 microM), which is much lower than those of the well-known anthracyclines daunorubicin and doxorubicin, the IC50 values of which are more than 100 micrograms/ml (> 170 microM). Kinetic studies demonstrated that mitoxantrone inhibited PKC in a competitive manner with respect to histone H1, and its Ki value was 6.3 microM (Ki values of daunorubicin and doxorubicin were 0.89 and 0.15 mM, respectively), and in a non-competitive manner with respect to phosphatidylserine and ATP. Inhibition of phosphorylation by mitoxantrone was observed with various substrates including S6 peptide, myelin basic protein and its peptide substrate derived from the amino-terminal region. Their IC50 values were 0.49 microgram/ml (0.95 microM), 1.8 micrograms/ml (3.5 microM), and 0.82 microgram/ml (1.6 microM), respectively. Mitoxantrone did not markedly inhibit the activity of cyclic AMP-dependent protein kinase, casein kinase I or casein kinase II, at concentrations of less than 10 micrograms/ml. On the other hand, brief exposure (5 min) of HL60 cells to mitoxantrone caused the inhibition of cell growth with an IC50 value of 52 ng/ml (0.1 microM). In HL60 cells, most of the PKC activity (about 90%) was detected in the cytosolic fraction. When HL60 cells exposed to 10 micrograms/ml mitoxantrone for 5 min were observed with fluorescence microscopy, the fluorescence elicited from mitoxantrone was detected in the extranuclear area. These results indicated that mitoxantrone is a potent inhibitor of PKC, and this inhibition may be one of the mechanisms of antitumor activity of mitoxantrone.

A tiaramide derivative, 5-chloro-3-(4-hydroxypiperadinocarbonylmethyl)benzothiazoline-2-one (HPR-611), a potent inhibitor of anaphylactic chemical mediator release--a distinctive feature from disodium cromoglycate

Effects of a tiaramide derivative, 5-chloro-3-(4-hydroxypiperadinocarbonylmethyl)benzothiazoline++ +-2-one (HPR-611), on anaphylactic chemical mediator release from rat peritoneal exudate cells (RPEC), guinea pig lung fragments (GPLF) and human lung fragments (HLF) were investigated in comparison with those of tiaramide and disodium cromoglycate (DSCG). HPR-611 at 10(-6) - 10(-4) g/ml showed a concentration-dependent inhibition of the histamine release from RPEC regardless of its pretreatment time. Tiaramide also inhibited the release with slightly less potency than HPR-611. The treatment of DSCG 1 min before antigen challenge markedly prevented the release but the inhibitory potency was clearly deteriorated by prolongation of the pretreatment time. Tiaramide tended to influence the anaphylactic release of histamine from GPLF with only 20% inhibition of the release at either 10(-5) or 10(-4) g/ml, whereas HPR-611 at 10(-5) and 10(-4) g/ml significantly suppressed the release in a concentration-dependent fashion. DSCG was not effective on that even at higher concentrations. Anaphylactic release of not only histamine but also immunoreactive leukotriene B4 (i-LTB4) and i-LTC4 from HLF was markedly inhibited by 10(-8) - 10(-4) g/ml of HPR-611. Tiaramide inhibited the release to a somewhat less extent than HPR-611, while nominal or no inhibitions by DSCG were found. From these results, it is clearly apparent that anti-allergic actions of HPR-611 are quite different from those of DSCG.

Significant role of peptide leukotrienes (p-LTs) in the antigen-induced contractions of human and guinea pig lung parenchymas and bronchi or tracheas in vitro

Chemical mediators responsible for the antigen-induced contractions of isolated, passively sensitized human and guinea pig lung parenchymas and bronchi or tracheas were evaluated by several antagonists and enzyme inhibitors, with emphasis on the effects of the potent and selective peptide leukotriene (p-LT) antagonist MCI-826. All of these preparations showed long-lasting contractions in response to an antigen challenge which lasted for more than 60 min. In either the human lung parenchyma and brochus or guinea pig lung parenchyma, pretreatment with 10(6) g/ml (2.4 x 10)-6) M) MCI-826 significantly inhibited the late phase at 10 to 60 min after the challenge of the contraction following slight suppression of the early phase. The early phase contractions of these preparations were moderately antagonized by 10(-6) g/ml mepyramine, but the late phases were not influenced or even rather enhanced. The combination treatment of MCI-826 with mepyramine additionally and markedly inhibited both phases of these preparations. On the other hand, although mepyramine apparently inhibited the early phase of the guinea pig tracheal contraction but not the late phase, no synergistic inhibitions of the contraction were observed when it was combined with MCI-826. The p-LT antagonist FPL 55712, atropine and indomethacin at 10(-6) g/ml either slightly inhibited or enhanced the contractions of human lung parenchymas, guinea pig tracheas and lung parenchymas, but the effects were not significant. From these results, it should be emphasized that p-LTs largely contribute to induction of the anaphylactic contractions of human lung parenchymas as well as human bronchi and guinea pig lung parenchymas but not guinea pig tracheas.

MCI-826 is a potent and selective antagonist of peptide leukotrienes (p-LTs) and has characteristics distinctive from those of FPL 55712

Antagonistic effects of a newly synthesized compound, (E)-2,2-diethyl-3'-[2-[2-(4-isopropyl)thiazolyl]ethenyl]succinanilic+ ++ acid sodium salt (MCI-826) on the contraction of the isolated guinea pig trachea and human bronchus induced by various agonists including peptide leukotrienes (p-LTs), histamine, acetylcholine (ACh), prostaglandin (PG) D2 and others were investigated and compared with the effects of a p-LT antagonist, FPL 55712, in some experiments. MCI-826 potently antagonized LTD4- and LTE4-induced contractions at extremely low concentrations in the isolated guinea pig trachea with pA2 values of 8.3 and 8.9, respectively, on a molar basis. These values indicated that MCI-826 is over 100 times stronger than FPL 55712. Similarly, MCI-826 at 10(-8) g/ml (2.4 x 10(-8) M) markedly antagonized LTD4-induced contractions of the isolated human bronchus. Although FPL 55712 fairly inhibited the 10(-9) g/ml LTC4-induced contraction of the isolated guinea pig trachea, MCI-826 had little effect on the contraction at high concentrations like 3 x 10(-6) g/ml (7.1 x 10(-6) M). MCI-826 modestly affected the other agonist-induced contractions and the resting tonus of the isolated guinea pig trachea at 10(-6) g/ml (2.4 x 10(-6) M) or higher concentrations, but FPL 55712 caused fair inhibition of some of those contractions and gradually lowered the resting tonus with time. These results indicate that MCI-826 is a highly potent and selective antagonist of LTD4 and LTE4 and can be a useful tool for biological and pharmacological experiments on p-LTs.

[The culture of mouse bone marrow-derived mast cells (BMMC) and the anaphylactic release of chemical mediators]

Bone marrow cells from BALB/c, C3H/He and WBB6F1+/+ mice were cultured for 5 wks in the presence of the culture supernatant from prokoweed mitogen-stimulated spleen cells to assess and compare the degree of growth, proliferation and chemical mediator release of the mast cells (BMMC) derived from them. BMMC, which were positive to alcian blue staining, were found in the suspension cells on the culture of the bone marrow cells of either species of mice after 2 wk culture. The percentages of BMMC in the suspension cells were increased with time of culture, reaching more than 90% after 5 wks. No differences in the growth and proliferation rate among BMMC from these three species were observed. However, in regard to the amount of anaphylactic leukotriene (LT) and histamine release. BMMC from BALB/c mice were superior to those from other species. From the above results, subsequent experiments were executed with BMMC from BALB/c mice. There was no obvious difference in the releasability of anaphylactic mediators among BMMC obtained at any stages of the passage during 4-12 wk culture. On the other hand, although BMMC cultured for 4 and 5 wks well responded to Ca ionophore A23187 for these mediator release, those for 6 to 12 wks obviously deteriorated with prolongation of the culture. The time course of the anaphylactic release of immunoreactive (i-) LTB4, i-LTC4 and histamine from BMMC revealed that almost maximum release was reached at 10, 20 and 5 min, respectively, after antigen challenge. Several drugs including antiallergics and beta-stimulants had no effect on their release. From these results, it is suggested that present BMMC may be inadequate cells for evaluation of antiallergic drugs that can inhibit the anaphylactic mediator release, but may be useful for the research of the mechanism of the release because the cells likely release the mediators without occurrence of complicated subordinate reactions.

Thrombin-induced human platelet aggregation is inhibited by protein-tyrosine kinase inhibitors, ST638 and genistein

We have investigated the involvement of protein-tyrosine kinases in thrombin-induced aggregation of human platelets, using ST638 and genistein which are known inhibitors of protein-tyrosine kinase. Preincubation of platelets with 50 microM of ST638 or 25 micrograms/ml of genistein completely blocked the platelet aggregation induced with 0.05 unit/ml of thrombin. The increase of protein-tyrosine phosphorylation bands (135-, 124-, 76-, 64-, and 60-kDa) induced with thrombin was also inhibited by these inhibitors in a dose-dependent manner. These inhibitors also blocked the platelet aggregation and protein-tyrosine phosphorylation induced with thrombin in aspirin-treated platelets. Increase of the intracellular Ca2+ concentration induced by thrombin was also inhibited by higher concentrations of genistein. These results suggest that the protein-tyrosine phosphorylation plays a certain role in platelet activation having some relation to the intracellular Ca2+ concentration.

Protein-tyrosine kinase p72syk is activated by wheat germ agglutinin in platelets

We previously reported a molecular cloning of porcine gene syk encoding a non-receptor type 72-kDa protein-tyrosine kinase (Taniguchi et al. (1991) J. Biol. Chem. 266, 15790-15796). In this study, we have demonstrated that p72syk is expressed in porcine platelets at 0.1-0.2% of total protein and that the lectin wheat germ agglutinin induces an activation of p72syk against both auto- and exogenous-substrate-phosphorylation in porcine platelets. The activation of p72syk was abrogated by the coexistence of N-acetyl-D-glucosamine with wheat germ agglutinin. These data suggest that p72syk is a candidate of responsible protein-tyrosine kinase for platelet activation and that cell surface glycoprotein is involved in the activation of p72syk in platelets.