Phosphate-binding tag, a new tool to visualize phosphorylated proteins

We introduce two methods for the visualization of phosphorylated proteins using alkoxide-bridged dinuclear metal (i.e. Zn(2+) or Mn(2+)) complexes as novel phosphate-binding tag (Phos-tag) molecules. Both Zn(2+)- and Mn(2+)-Phos-tag molecules preferentially capture phosphomonoester dianions bound to Ser, Thr, and Tyr residues. One method is based on an ECL system using biotin-pendant Zn(2+)-Phos-tag and horseradish peroxidase-conjugated streptavidin. We demonstrate the electroblotting analyses of protein phosphorylation status by the phosphate-selective ECL signals. Another method is based on the mobility shift of phosphorylated proteins in SDS-PAGE with polyacrylamide-bound Mn(2+)-Phos-tag. Phosphorylated proteins in the gel are visualized as slower migration bands compared with corresponding dephosphorylated proteins. We demonstrate the kinase and phosphatase assays by phosphate affinity electrophoresis (Mn(2+)-Phos-tag SDS-PAGE).

FANCI phosphorylation functions as a molecular switch to turn on the Fanconi anemia pathway

In response to DNA damage or replication fork stress, the Fanconi anemia pathway is activated, leading to monoubiquitination of FANCD2 and FANCI and their colocalization in foci. Here we show that, in the chicken DT40 cell system, multiple alanine-substitution mutations in six conserved and clustered Ser/Thr-Gln motifs of FANCI largely abrogate monoubiquitination and focus formation of both FANCI and FANCD2, resulting in loss of DNA repair function. Conversely, FANCI carrying phosphomimic mutations on the same six residues induces constitutive monoubiquitination and focus formation of FANCI and FANCD2, and protects against cell killing and chromosome breakage by DNA interstrand cross-linking agents. We propose that the multiple phosphorylation of FANCI serves as a molecular switch in activation of the Fanconi anemia pathway. Mutational analysis of putative phosphorylation sites in human FANCI indicates that this switch is evolutionarily conserved.

Recognition of phosphate monoester dianion by an alkoxide-bridged dinuclear zinc(II) complex

Recognition of phosphate monoester dianion by an alkoxide-bridged dinuclear zinc(II) complex (Zn2L3+) has been studied (L = alkoxide species of 1,3-bis[bis(pyridin-2-ylmethyl)amino]propan-2-ol). Potentiometric pH titration study disclosed a 1 : 1 phenyl phosphate complexation with Zn2L3+ in aqueous solution. The dissociation constant (= [Zn2L3+][PhOPO3(2-)]/[Zn2L3+-PhOPO3(2-)]) is an extremely small value of 2.5 x 10(-8) mol dm(-3) at 25 degrees C with I = 0.10 (NaNO3). The X-ray crystal analysis of the dizinc(II) complex with p-nitrophenyl phosphate showed that the phosphate dianion binds as a bridging ligand to the two zinc(II) ions.

Purification and identification of an angiotensin I-converting enzyme inhibitor from soy sauce

The inhibitory activity of an angiotensin I-converting enzyme (ACE) detected in soy sauce was fractionated into two major fractions of high molecular weight (Hw) and low molecular weight (Lw) by gel filtration chromatography on Bio-gel P-2 after treating with ethanol. The Hw fraction reduced the blood pressure in hypertensive rats after orally administering, while the Lw fraction did not. The ACE inhibitor in the Hw fraction was further purified by Dowex 50W ion-exchange chromatography and four subsequent steps of HPLC. On the basis of the SIMS-mass spectrum, NMR spectrum and other characteristics, the purified ACE inhibitor was identified as nicotianamine (N-[N-(3-amino-3-carboxypropyl)-3-amino-3-carboxypropyl]azetidine-2- carboxylic acid). The IC50 value for this ACE was 0.26 microM.

Improved Phos-tag SDS-PAGE under neutral pH conditions for advanced protein phosphorylation profiling

We describe an improved Phos-tag SDS-PAGE (Zn(2+)-Phos-tag SDS-PAGE) using a dizinc(II) complex of Phos-tag acrylamide in conjunction with a Bis-tris-buffered neutral-pH gel system to detect shifts in the mobility of phosphoproteins. An existing technique (Mn(2+)-Phos-tag SDS-PAGE) using a polyacrylamide-bound Mn(2+)-Phos-tag and a conventional Laemmli's buffer system under alkaline pH conditions has limitations for separating certain phosphoproteins. The major improvements were demonstrated by visualizing novel up-shifted bands of commercially available pepsin, recombinant Tau treated in vitro with tyrosine kinases, and endogeneous β-catenin in whole-cell lysates. Additionally, the Zn(2+)-Phos-tag SDS-PAGE gels showed better long-term stability than the Mn(2+)-Phos-tag SDS-PAGE gels. We can therefore provide a simple, convenient, and more reliable homemade gel system for phosphate-affinity SDS-PAGE.

Label-free kinase profiling using phosphate affinity polyacrylamide gel electrophoresis

Herein we describe three applications of label-free kinase profiling using a novel type of phosphate affinity polyacrylamide gel electrophoresis. The phosphate affinity site is a polyacrylamide-bound dinuclear Mn2+ complex that enables the mobility shift detection of phosphorylated proteins from their nonphosphorylated counterpart. The first application is in vitro kinase activity profiling for the analysis of varied phosphoprotein isotypes in phosphorylation status. The activity profiles of six kinds of kinases, glycogen synthase kinase-3beta, cyclin-dependent kinase 5/p35, protein kinase A, mitogen-activated protein kinase (MAPK), casein kinase II, and calmodulin-dependent protein kinase II, were determined using a substrate protein, Tau, which has a number of phosphorylation sites. Each kinase demonstrated characteristic multiple electrophoresis migration bands up-shifted from the nonphosphorylated Tau due to differences in the phosphorylation sites and stoichiometry. The second application is in vivo kinase activity profiling for the analysis of protein phosphorylation involved in intracellular signal transduction. The time course changes in the epidermal growth factor-induced phosphorylation levels of Shc and MAPK in A431 cells were visualized as highly up-shifted migration bands by subsequent immunoblotting with anti-Shc and anti-MAPK antibodies. The third application is in vitro kinase inhibition profiling for the quantitative screening of kinase-specific inhibitors. The inhibition profile of a tyrosine kinase, Abl (a histidine-tagged recombinant mouse Abl kinase), was determined using the substrate Abltide-GST (a fusion protein consisting of a specific substrate peptide for Abl and glutathione S-transferase) and the approved drug Glivec (an ATP competitor). In the kinase assay, the slower migration band, monophosphorylated Abltide-GST, increased time-dependently, whereas the faster migration band, nonphosphorylated Abltide-GST, decreased. The dose-dependent inhibition of Glivec was determined by a change in the ratio of the faster and slower migration bands, which showed an IC50 value of 1.6 microM in the presence of 0.10 mM ATP.

Detection and Quantification of On-Chip Phosphorylated Peptides by Surface Plasmon Resonance Imaging Techniques Using a Phosphate Capture Molecule

We describe herein a detection and quantification system for on-chip phosphorylation of peptides by surface plasmon resonance (SPR) imaging techniques using a newly synthesized phosphate capture molecule (i.e., biotinylated zinc(II) complex). The biotinylated compound is a dinuclear zinc(II) complex that is suitable for accessing phosphate anions as a bridging ligand on the two zinc(II) ions. The compound was exposed on the peptide array and detected with streptavidin (SA) via a biotin-SA interaction by SPR imaging. In the conventional method using antibody, both anti-phosphoserine and anti-phosphotyrosine antibodies were required for phosphoserine and phosphotyrosine detection, respectively. Detection of the phosphate group by the zinc(II) complex, however, was independent of the phosphorylated amino acid residues. The calibration curve for the phosphorylation ratios was established with a calibration chip, on which phosphoserine-containing peptide probes were immobilized. The peptide probes, which were phosphorylated on the surface by protein kinase A, were detected and quantified by SPR imaging using the zinc(II) complex, SA, and anti-SA antibody. The reaction rate and the kinetics of on-chip phosphorylation were also evaluated with the peptide array. The phosphorylation ratio was saturated at approximately 20% in 2 h in this study.

Novel immobilized zinc(II) affinity chromatography for phosphopeptides and phosphorylated proteins

Immobilized metal ion affinity chromatography (IMAC) is now a widely accepted technique for the separation of natural or artificial products that is beginning to find industrial applications. Here, we introduce a novel procedure for the separation of phosphopeptides and phosphorylated proteins by immobilized zinc(II) affinity chromatography. The phosphate-binding site of the affinity gel is an alkoxide-bridged dinuclear zinc(II) complex, the 1,3-bis[bis(pyridin-2-ylmethyl)amino]propan-2-olato dizinc(II) complex (Phos-tag), which is linked to a highly cross-linked 4% (w/v) agarose. The affinity gel (Phos-tag agarose) was prepared by the quantitative reaction of N-hydroxysuccinimide-activated Sepharose and a Phos-tag derivative having a 2-aminoethylcarbamoyl group in dry CH3CN. Phosphopeptides were retrieved in a quantitative and highly selective manner by a spin column method using Phos-tag agarose at room temperature. Furthermore, in this study, we demonstrate a simple, rapid, and reusable affinity column chromatography for the separation of phosphorylated proteins such as ovalbumin, alpha(s1)-casein, and beta-casein at physiological pH.

Phos-tag SDS-PAGE systems for phosphorylation profiling of proteins with a wide range of molecular masses under neutral pH conditions

We have previously reported a neutral-pH gel system buffered with Bis-Tris hydrochloride (Bis-Tris-HCl) in Zn(2+)-Phos-tag SDS-PAGE for advanced profiling of phosphoproteins with molecular masses of 10-200 kDa. In the current work, we describe characteristics of two neutral-pH gel systems, Bis-Tris-HCl and Tris-acetic acid (Tris-AcOH), based on comparative studies of the separation of a wide range of proteins with molecular masses from 10 to 350 kDa. For 10-200 kDa cellular proteins, the Bis-Tris-HCl system showed a higher resolving power in a 2-D fluorescence DIGE analysis of certain phosphoproteins, e.g. histone H3 (15 kDa) and elongation factor 2 (95 kDa). Furthermore, there was a large difference in the 1-D migration patterns of phosphorylated species of extracellular signal-regulated kinases 1 and 2 (ERK1/2, 44/42 kDa), which arise from changes in the phosphorylation status of the Thr-202 and Tyr-204, in the two buffer systems at the same concentration of Zn(2+)-Phos-tag. In contrast, shifts in the mobility of various phosphorylated species of a high-molecular-mass protein, ataxia telangiectasia-mutated kinase (ATM, 350 kDa), could only be detected in the Tris-AcOH system with a 3% w/v polyacrylamide gel strengthened with 0.5% w/v agarose.

Enrichment of phosphorylated proteins from cell lysate using a novel phosphate-affinity chromatography at physiological pH

While phosphoproteins have attracted great interest toward the post-genome research (e.g. clinical diagnosis and drug design), there have been few procedures for the specific enrichment of native phosphoproteins from cells or tissues. Here, we describe a simple and efficient protocol to enrich phosphoproteins comprehensively from a complex mixture containing solubilized cellular proteins. This method is based on immobilized metal affinity chromatography using a phosphate-binding tag molecule (i.e. a dinuclear zinc(II) complex) attached on a highly cross-linked agarose. The binding, washing, and elution processes were all conducted without a detergent or a reducing agent at pH 7.5 and room temperature. An additive, 1.0 M CH3COONa, was necessary in the binding and washing buffers (0.10 M Tris-CH3COOH, pH 7.5) to prevent the nonphosphorylated protein from binding. The absorbed phosphoproteins were eluted using a mixed buffer solution (pH 7.5) consisting of 0.10 M Tris-CH3COOH, 10 mM NaH2PO4-NaOH, and 1.0 M NaCl. In this study, we demonstrate a typical example of phosphate-affinity chromatography using an epidermal growth factor-stimulated A431 cell lysate. The total time for the column chromatography (1 mL gel scale) was less than 1 h. The strong enrichment of the phosphoproteins into the elution fraction was evaluated using SDS-PAGE followed by Western blotting analysis.

Separation of phosphoprotein isotypes having the same number of phosphate groups using phosphate-affinity SDS-PAGE

Herein, we demonstrate the separation of phosphoprotein isotypes having the same number of phosphate groups using phosphate-affinity SDS-PAGE. The phosphate-affinity site is a polyacrylamide-bound Phos-tag that enables the mobility shift detection of phosphoproteins from their nonphosphorylated counterparts. As the first practical example of the separation, we characterized the monophosphorylated Tau isotypes by each of three tyrosine kinases, c-Abl, MET, and Fyn. Each monophosphoisotype phosphorylated at the Tyr-394, Tyr-197, or Tyr-18 was detected as three distinct migration bands. As a further application, we extended this technique to the mobility shift analysis of His and Asp phosphoisotypes in the Sinorhizobium meliloti FixL/FixJ two-component system. FixL is autophosphorylated at the His-285 with ATP, and the phosphate group is transferred to the Asp-54 of FixJ and subsequently removed by the FixL phosphatase activity. Using this method, we first performed simultaneous detection of the phosphorylated and nonphosphorylated isotypes of FixL and FixJ generated in their phosphotransfer reaction in vitro. As a result, a monophosphoisotype of FixL containing the phosphorylated His residue was confirmed. As for FixJ, on the other hand, two monophosphoisotypes were detected as two distinct migration bands. One is a well-known isotype phosphorylated at the Asp-54. The other is a novel isotype phosphorylated at the His-84.

Distinct sites regulating grayanotoxin binding and unbinding to D4S6 of Na(v)1.4 sodium channel as revealed by improved estimation of toxin sensitivity

Grayanotoxin (GTX) exerts selective effects on voltage-dependent sodium channels by eliminating fast sodium inactivation and causing a hyperpolarizing shift in voltage dependence of channel activation. In this study, we adopted a newly developed protocol that provides independent estimates of the binding and unbinding rate constants of GTX (k(on) and k(off)) to GTX sites on the sodium channel protein, important in the molecular analysis of channel modification. Novel GTX sites were determined in D2S6 (Asn-784) and D3S6 (Ser-1276) by means of site-directed mutagenesis; the results suggested that the GTX receptor consists of the S6 transmembrane segments of four homologous domains facing the ion-conducting pore. We systematically introduced at two sites in D4S6 (Na(v)1.4-Phe-1579 and Na(v)1.4-Tyr-1586) amino acid substituents with residues containing hydrophobic, aromatic, charged, or polar groups. Generally, substitutions at Phe-1579 increased both k(on) and k(off), resulting in no prominent change in dissociation constant (K(d)). It seems that the smaller the molecular size of the residue at Na(v)1.4-Phe-1579, the larger the rates of k(on) and k(off), indicating that this site acts as a gate regulating access of toxin molecules to a receptor site. Substitutions at Tyr-1586 selectively increased k(off) but had virtually no effect on k(on), thus causing a drastic increase in K(d). At position Tyr-1586, a hydrophobic or aromatic amino acid side chain was required to maintain normal sensitivity to GTX. These results suggest that the residue at position Tyr-1586 has a more critical role in mediating GTX binding than the one at position Phe-1579. Here, we propose that the affinity of GTX to Na(v)1.4 sodium channels might be regulated by two residues (Phe and Tyr) at positions Phe-1579 and Tyr-1586, which, respectively, control access and binding of GTX to its receptor.

Terreic acid, a quinone epoxide inhibitor of Bruton's tyrosine kinase

Bruton's tyrosine kinase (Btk) plays pivotal roles in mast cell activation as well as in B cell development. Btk mutations lead to severe impairments in proinflammatory cytokine production induced by cross-linking of high-affinity IgE receptor on mast cells. By using an in vitro assay to measure the activity that blocks the interaction between protein kinase C and the pleckstrin homology domain of Btk, terreic acid (TA) was identified and characterized in this study. This quinone epoxide specifically inhibited the enzymatic activity of Btk in mast cells and cell-free assays. TA faithfully recapitulated the phenotypic defects of btk mutant mast cells in high-affinity IgE receptor-stimulated wild-type mast cells without affecting the enzymatic activities and expressions of many other signaling molecules, including those of protein kinase C. Therefore, this study confirmed the important roles of Btk in mast cell functions and showed the usefulness of TA in probing into the functions of Btk in mast cells and other immune cell systems. Another insight obtained from this study is that the screening method used to identify TA is a useful approach to finding more efficacious Btk inhibitors.

Mobility shift detection of phosphorylation on large proteins using a Phos-tag SDS-PAGE gel strengthened with agarose

We describe a novel technique of phosphate-affinity SDS-PAGE using Phos-tag to analyze large phosphoproteins with molecular masses of more than 200 kDa. The protein phosphoisotypes were clearly separated as up-shifted migration bands in a 3% w/v polyacrylamide gel containing 20 microM Phos-tag and 0.5% w/v agarose. In subsequent immunoblotting, the procedure permitted the determination of the phosphoisotypes of high-molecular-mass proteins, such as mTOR (289 kDa), ATM kinase (350 kDa), and 53BP1 (213 kDa).

Compound heterozygous deletion of the PROP-1 gene in children with combined pituitary hormone deficiency

Mutations in the prophet of Pit-1 gene (PROP1) have been shown to be responsible for combined pituitary hormone deficiency (CPHD) with deficiencies of growth hormone (GH), Prolactin (Prl), thyroid-stimulating hormone (TSH) and gonadotropins. We previously reported that homozygosity for a 2bp deletion in exon 2 (296delGA) accounted for CPHD in three patients from two Russian families. Here we report a second mutational hot spot in exon 2. This 2bp 149delGA deletion results in a frame shift that leads to the same serine to stop codon change at codon 109 (S109X). The predicted proteins are each truncated at residue 108 but diverge from the wild type sequence at different points in the homeodomain. Compound heterozygosity for the two mutations (149delGA/296delGA) was detected in 5 of 14 CPHD children from 4 families (36%). This provides the first evidence of heterozygosity for two common deletions as a cause of CPHD in Russian children.

Advances in Phos-tag-based methodologies for separation and detection of the phosphoproteome

This review article describes analytical techniques based on the phosphate-binding tag molecule "Phos-tag", which is an alkoxide-bridged dinuclear metal complex with 1,3-bis(pyridin-2-ylmethylamino)propan-2-olate, for studying the protein phosphorylome. The dinuclear zinc(II) complex forms a stable 1:1 complex with a phosphate monoester dianion in an aqueous solution under conditions of neutral pH. By using a series of functional Phos-tag derivatives, our group has developed novel techniques that are useful in studies on kinomics and phosphoproteomics. Among the derivatives, a series of biotinylated Phos-tag derivatives have been used as molecular tools in applications such as Western blotting for comprehensive detection of phosphorylated proteins and in highly sensitive peptide microarray-based techniques for the detection of kinase activities in biological samples. The review also gives an outline of phosphate affinity electrophoresis, in which immobilized Phos-tag molecules in a general polyacrylamide gel are used to separate proteins and detect differences in their phosphorylation status. This technique permits quantitative analyses of multiple phosphorylation statuses of individual cellular proteins and their time-dependent changes. Conventional mass spectrometry-based shotgun techniques used in phosphoproteomics detect the phosphorylation modification of proteins in peptide fragments, whereas the Phos-tag electrophoresis technique permits the direct analysis of the phosphorylation status of full-length proteins. The technique therefore provides a greater understanding of the detailed properties of particular proteins involved in specific physiological and pathological events. This article is part of a Special Issue entitled: Medical Proteomics.

Rarity of PIT1 involvement in children from Russia with combined pituitary hormone deficiency

To ascertain the molecular background of combined pituitary hormone deficiency, screening for mutations in the pituitary-specific transcription factor (Pit-1/GHF-1) gene (PIT1) was performed on a cohort of 15 children from Russia with combined growth hormone (GH)/prolactin (Prl)/thyroid-stimulating hormone (TSH) deficiency. The group of patients, suspected of PIT1 mutations, consisted of four familial cases (seven patients) and eight sporadic cases. All had complete GH deficiency and complete or partial Prl and TSH deficiency. Direct sequencing of all six exons of PIT1 and its promoter region showed a C to T transition mutation at codon 14 of exon 1 in a 3 8/12-year-old girl. This novel PIT1 mutation results in a proline to leucine substitution (P14L). The patient was heterozygous for mutant and normal alleles. The heterozygous P14L mutation was also present in her mother as well as in her maternal aunt and grandmother, all of whom were phenotypically normal. There was no mutation in the father's DNA, suggesting the need for reevaluation of genomic imprinting. In other children of our series, no mutation in PIT1 or in its promotor region was identified. This is the first report on the analysis of PIT1 and its promoter region in Russian children with GH/Prl/TSH deficiency. However, as the involvement of PIT1 mutation is rare in Russia, the other negative cases need to be analyzed for another candidate gene responsible for combined GH/Pr/TSH deficiency.

Activation of MAP kinase cascade induced by human pancreatic phospholipase A2 in a human pancreatic cancer cell line

We have found that the growth of human pancreatic cancer cells MIAPaCa-2, induced by human pancreatic phospholipase A2 group I (hPLA2-I), is mediated via its specific receptor but not via its catalytic property. The present study showed that the activation of mitogen-activated protein kinase (MAPK) cascade in MIAPaCa-2 cells is induced by hPLA2-I: this digestive enzyme induced phosphorylation of MEK1/2, p44/42 MAPK and ATF-2, and the phosphorylation in the MAPK cascade was inhibited after the cells were pre-incubated with a selective inhibitor of MEK, PD98059. In addition, this inhibitor dose-dependently blocked the hPLA2-I-induced MIAPaCa-2 proliferation, suggesting that activation of the MAPK cascade is essential for the hPLA2-I-induced MIAPaCa-2 proliferation.

Synthetic ciguatoxins selectively activate Nav1.8-derived chimeric sodium channels expressed in HEK293 cells

The synthetic ciguatoxin CTX3C has been shown to activate tetrodotoxin (TTX)-sensitive sodium channels (Na(v)1.2, Na(v)1.4, and Na(v)1.5) by accelerating activation kinetics and shifting the activation curve toward hyperpolarization (Yamaoka, K., Inoue, M., Miyahara, H., Miyazaki, K., and Hirama, M. (2004) Br. J. Pharmacol. 142, 879-889). In this study, we further explored the effects of CTX3C on the TTX-resistant sodium channel Na(v)1.8. TTX-resistant channels have been shown to be involved in transducing pain and related sensations (Akopian, A. N., Sivilotti, L., and Wood, J. N. (1996) Nature 379, 257-262). Thus, we hypothesized that ciguatoxin-induced activation of the Na(v)1.8 current would account for the neurological symptoms of ciguatera poisoning. We found that 0.1 mum CTX3C preferentially affected the activation process of the Na(v)1.8 channel compared with those of the Na(v)1.2 and Na(v)1.4 channels. Importantly, without stimulation, 0.1 mum CTX3C induced a large leakage current (I (L)). The conductance of the I (L) calculated relative to the maximum conductance (G (max)) was 10 times larger than that of Na(v)1.2 or Na(v)1.4. To determine the molecular domain of Na(v)1.8 responsible for conferring higher sensitivity to CTX3C, we made two chimeric constructs from Na(v)1.4 and Na(v)1.8. Chimeras containing the N-terminal half of Na(v)1.8 exhibited a large response similar to wild-type Na(v)1.8, indicating that the region conferring high sensitivity to ciguatoxin action is located in the D1 or D2 domains.

A mutational hot spot in the Prop-1 gene in Russian children with combined pituitary hormone deficiency

Combined pituitary hormone deficiency (CPHD), including growth hormone (GH), prolactin (Prl) and thyroid-stimulating hormone (TSH) in children is now considered a heterogeneous syndrome. Recent findings on expression of mouse pituitary-specific homeodomain factors demonstrate dependence of adenopituitary ontogeny on interactive expression of these factors, suggesting their involvement in etiology of CPHD. Prophet of Pit-1 (Prop-1) gene, a novel pituitary-specific homeodomain factor, was analyzed in 14 Russian children with CPHD, in whom Pit-1 gene was intact. We found a mutational hot spot in three patients from two families in homeodomain part of the second exon of Prop-1 gene. The common 2-base pair deletion (GA296) in the homozygous state resulted in a Serine to Stop codon (S109X) substitution and generated a truncated Prop-1 protein. Parents were phenotypically normal and heterozygous for GA296 deletion, indicating an autosomal recessive inheritance. These results demonstrate a novel type of Prop-1 gene mutation as one of the causes of CPHD in Russian patients.

Human pancreatic phospholipase A2 stimulates the growth of human pancreatic cancer cell line

Phospholipase A2 (PLA2) from human pancreas, designated hPLA2-I, functions as a digestive enzyme. Interestingly, the present study demonstrated that the mature form of hPLA2-I stimulated the growth of a human pancreatic cancer cell line MIAPaCa-2, whereas the pro-form was ineffective. PLA2s from Laticauda semifasciata fraction I, Crotalus adamanteus venom, Streptomyces violaceoruber and bee venom, showed no proliferative effect to the growth of MIAPaCa-2. The Scatchard plot analysis revealed that the MIAPaCa-2 cell had a specific binding site for the mature hPLA2-I. The equilibrium binding constant (Kd) and the maximum binding capacity (Bmax) were 2.6 nM and 0.4 fmol/10(6) cells, respectively. These results suggest that the mature hPLA2-I, but not the pro-form, may function as a growth factor of pancreas carcinoma via the specific binding site.