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PubMedDate not supplied

Urinary bivalent sulfur metabolites of phenanthrene excreted by the rat and guinea pig.

After the administration of phenanthrene (50 mg/kg, ip) to young adult male rats and guinea pigs, a series of bivalent sulfur urinary metabolites were isolated and characterized by gas chromatography and gas chromatography-mass spectrometry. Seven methylthio metabolites were isolated from the neutral fraction of hydrolyzed rat urine, whereas only two were detected in guinea pig urine. The major methylthio metabolite excreted by each species was 9-hydroxy-10-methylthio-9, 10-dihydrophenanthrene. This was observed as a second-day metabolite in the rat, and its appearance was accompanied by 9-phenanthrol. In addition to the methylthio compounds, which were excreted predominantly as glucuronides, six acidic bivalent sulfur metabolites were isolated from hydrolyzed rat urine and identified by GC/MS; five were present in hydrolyzed guinea pig urine. The major acidic metabolite in hydrolyzed rat urine was the hydroxydihydromercapturic acid N-acetyl-S-(9-hydroxy-9, 10-dihydro-10-phenanthryl)-L-cysteine. The major acidic metabolite in guinea pig urine was the mercaptoacetic acid S-(9-hydroxy-9, 10-dihydro-10-phenanthryl)mercaptoacetic acid, but the hydroxydihydromercapturic acid was also present.

Animals↗
PubMed1980

[Role of bivalent and monovalent cations in the functioning of myosin ATPase].

The effects of bivalent (Mg2+, Ca2+, Sr2+) and monovalent (K+, Na+, NH4+) cations on the ATPase activity of subfragment 1 of myosin (SI) with a decreased Mg2+ content (EDTA-SI) were studied. Mg2+ activate the EDTA-SI ATPase, but only in the absence of other activating cations. K+, NH4+, a2+ and Sr2+ have a much stronger activating effect on EDTA-SI ATPase than on Mg-SI (SI enriched with Mg2+) ATPase. Monovalent cations inhibit Mg2+-ATPase and Ca2+-ATPase of EDTA-SI, while K+ and NH4+ activate Sr2+-ATPase of EDTA-SI. Based on experimental results and literary data, a hypothesis on the participation of the cations in the functioning of myosin ATPase was postulated. This hypothesis entails the existence of two closely interconnected cation-binding sites in the vicinity of the myosin active center (one for bivalent and one for monovalent cations); the ATPase activity of myosin is at any moment dependent on the nature of cations present in these two sites. An attempt to explain the role of the cations in the accomplishment of the ATPase reaction by myosin was made.

Adenosine Triphosphatases↗
PubMedDate not supplied

[Functional significance of bivalent iron and manganese oxidation in Leptothrix pseudoochraceae].

The effect of oxidation of bivalent compounds of iron and manganese was studied on the growth of filamentous iron bacteria. The stimulating action of these metals could not be attributed to utilization of the energy of their oxidation in the assimilation of carbon dioxide or in lithoheterotrophic processes. The cells yield increased because the metal ions removed the toxic metabolite, hydrogen peroxide, which was formed in the respiratory chain upon oxidation of an organic substrate. This function of bivalent metals in detoxication of hydrogen peroxide accounts for the ecological confinement of iron bacteria to certain environment.

Culture Media↗
PubMed1980

Monogamous bivalency of IgG antibodies. I. Deficiency of branched ABHI-active oligosaccharide chains on red cells of infants causes the weak antiglobulin reactions in hemolytic disease of the newborn due to ABO incompatibility.

This study shows that monogamous bivalency of human IgG anti-A and anti-B is necessary to maintain sensitization of red cells in the antiglobulin test. On red cells of infants and of adults of i phenotype, the known deficiency of branched ABHI-active oligosaccharide chains limits monogamous bivalency, and these accounts for the relatively weak direct antiglobulin reactions in hemolytic disease of the newborn due to ABO incompatbility. One corollary of this finding is that there is strong biologic selection against the transition on fetal red cells from the straight-chain i phenotype to branched-chain I phenotype, since such branching of cell-surface oligosaccharide chains would compromise ABO-incompatible pregnancies.

ABO Blood-Group System↗
PubMed1994

Synthesis and muscarinic receptors affinity of a series of antagonist bivalent ligands.

A series of bivalent ligands (2-8) derived from 2,2-diphenyl-[1,3]-dioxolan-4-ylmethyl-dimethylamine methiodide 1 has been synthesized and tested to evaluate affinity and selectivity for M1, M2 and M3 muscarinic receptor subtypes. In order to study the contribution of the spacer and of a second cationic head to the binding process, unsymmetrical ligands (9,10) have also been prepared. The results, expressed in terms of pA2 values, show that, although the spacer negatively affects the interaction of the bivalent ligands with the three receptor subtypes, affinity and selectivity are modulated by its length; this indicates that the pharmacophore binding sites are organized differently with respect to their mutual proximity and orientation, in each receptor subtype.

(4-(m-Chlorophenylcarbamoyloxy)-2-butynyl)trimethy↗
PubMed1994

Partial inhibition of platelet aggregation and fibrinogen binding by a murine monoclonal antibody to GPIIIa: requirement for antibody bivalency.

We produced a murine monoclonal antibody, 7H2, and localized its epitope to one or more small regions on platelet glycoprotein (GP) IIIa. 7H2-IgG and 7H2-F(ab')2 completely inhibit platelet aggregation and fibrinogen binding at low agonist concentrations, but only partially inhibit aggregation and fibrinogen binding at high agonist concentrations; 7H2-Fab has no effect on aggregation or fibrinogen binding at any agonist concentration. 7H2-IgG binds to the entire platelet population as judged by flow cytometry. At near saturating concentrations, approximately 40,000 7H2-IgG antibody molecules bind per platelet. In contrast, approximately 80,000 7H2 Fab molecules bind per platelet, suggesting that 7H2-IgG binding is bivalent. 7H2 was unable to inhibit fibrinogen binding to purified, immobilized GPIIb/IIIa. These data indicate that the bivalent binding of 7H2 to GPIIIa is required for its partial inhibition of fibrinogen binding to platelets, perhaps through dimerization of GPIIb/IIIa surface receptors (or more complex GPIIb/IIIa redistribution triggered by 7H2 binding) resulting in limited accessibility of fibrinogen to its binding site(s).

Animals↗
PubMed1995

Simultaneous cross-linking by two nontriggering bivalent ligands causes synergistic signaling of IgE Fc epsilon RI complexes.

We have used two bivalent ligands that bind IgE to study the relationship between the aggregation of receptors with high affinity for IgE (Fc epsilon RI) and the responses (receptor immobilization, Ca2+ influx, and degranulation) of rat basophilic leukemia (RBL-2H3) cells. One of these is a symmetric bivalent ligand, N,N'-bis[[epsilon-[(2,4-dinitrophenyl)amino]caproyl]-L-tyrosyl]-L- cystine ((DCT)2-cys), which binds specifically to the combining sites of a mAb anti-DNP IgE and efficiently cross-links cell surface IgE, but does not trigger significant degranulation or increases in intracellular Ca2+. Several lines of evidence, including lateral mobility measurements, indicate that this ligand preferentially forms stable cyclic complexes containing two (DCT)2-cys and two IgE. The second ligand is a mAb anti-IgE, B1E3, which causes lateral mobility changes consistent with dimerized IgE-Fc epsilon RI and also does not trigger increases in intracellular Ca2+ or degranulation. The two ligands together trigger robust responses. In the presence of B1E3, (DCT)2-cys causes immobilization of IgE-Fc epsilon RI in a broad concentration range; in a more narrow concentration range, it is a potent stimulant of changes in both degranulation and Ca2+. We have compared the dose-response curves for cellular activation to simulated IgE aggregation curves, i.e., curves that predict the equilibrium IgE aggregate size distribution as a function of the (DCT)2-cys concentration. Our results indicate that maximal cellular activation occurs at a much higher (DCT)2-cys concentration than maximal IgE aggregation. When IgE aggregation is maximal, almost all aggregated IgE is in cyclic dimers. Thus, cyclic dimers appear to be functionally ineffective, even after they have been cross-linked by B1E3. Aggregated IgE-Fc epsilon RI that is effective in stimulating a cellular response may have particular structural or dynamic properties that allow critical interactions for initiating the signaling cascade.

Animals↗
PubMed1978

Histamine release due to bivalent penicilloyl haptens: control by the basophil plasma membrane.

We describe the characteristics of in vitro histamine release from human basophils passively sensitized with serum from a penicillin-allergic individual. The histamine release is induced by a synthetic bivalent hapten, bis benzylpenicilloyl 1,6 diaminohexane (BPO)2. We present data on the effect of a monovalent hapten, benzylpenicilloyl formyl-L-lysine (BPO)1, on the histamine release. We also examine how histamine release depends on the concentration of serum used for passive sensitization, the source of cells used for passive sensitization, and the time allowed for histamine release. We interpret these experiments in terms of a theory of equilibrium binding of bivalent haptens to cell surface antibody that is presented in the previous paper. The results are consistent with the idea that the amount of histamine release is controlled by the number of cross-linked IgE molecules on the cell surface. In particular, the histamine dose-response curve rises because cross-links rise, has a maximum because the cross-links are a maximum, and falls because the cross-links fall.

Basophils↗
PubMedDate not supplied

Effects of tricyclic compounds on membrane binding of bivalent cations, activities of acetylcholinesterase and some tissue proteases.

A tricyclic compound tetrahydroaminoacridine is known to improve the cognitive function in Alzheimer's disease. The possible mechanism of action of acridine and structurally related tricyclic compounds was studied on the bivalent cation content of bacterial membrane, rat brain acetylcholinesterase and some tissue proteases in model experiments. Acridine orange and disubstituted chlorpromazine (CPZ) derivatives lowered Ca2+ and Mg2+ binding and membrane polarization in the simplest biological membrane (E. coli), as revealed by reactor neutron activation analysis. Acetylcholinesterase (AChE) was inhibited by CPZ, 3,7,8-trihydroxy-CPZ, acridine orange partially saturated desipramine, imipramine, trans-clopenthixol and tetrahydrocannabidiolic at 10(-4) to 10(-5). A metalloproteinase, MMP-7-ase, was inhibited by tetrahydrocannabidiolic acid, 3,7,8-trihydroxy-CPZ, acridine orange but other tissue proteinases, ATN-ase and cathepsin B, were less sensitive to these compounds. (ATN-ase is an acetyltyrosine-p-nitroanilide splitting enzyme, a serine protease). The chelate complex forming ability and electron donor capacity of the compounds may play a role in the biological effects tested. It is assumed that compounds which do not displace bivalent cations in membranes may exert an inhibitory effect on AChE, and that metalloproteinase enzymes may be promising for the treatment of degenerative brain diseases.

Alzheimer Disease↗
PubMed1993

[An unusual heteromorphic bivalent in the common vole (Microtus arvalis) from Byelarus].

Electron microscopic analysis was carried out on the synaptonemal complexes of ten male common voles (Microtus arvalis) caught of 1990 in Byelorussia. In the early pachytene stage of spermatocytes of four males heteromorphic bivalent has been found in one of five large autosomes. In the central region of the bivalent one of the lateral elements is in the form of a D-loop, characteristic of insertion/deletion heterozygotes. However, high-resolution G-band staining of mitotic chromosomes from fibroblasts showed no significant differences in the G-band patterns between homologues.

Animals↗
PubMed1996

Bispecific antibody and iodine-131-labeled bivalent hapten dosimetry in patients with medullary thyroid or small-cell lung cancer.

UNLABELLED: The purpose of this study was to estimate the dose delivered to tumor targets and normal tissues after two-step injection of an anti-CEA/anti-DTPA-In (F6-734) bispecific antibody and a 131I-labeled di-DTPA in-TL bivalent hapten in patients with medullary thyroid carcinoma (MTC) and small-cell lung cancer (SCLC). METHODS: Five patients with persistent disease or recurrences of MTC and five patients with primary SCLC or relapse were studied. In a first step, 0.1 to 0.3 mg/kg of F6-734 bispecific antibody was injected intravenously. Four days later, 6 nmole (5.8 to 9.8 mCi) of 131I-labeled di-DTPA in-TL bivalent hapten were injected. Quantitative imaging was performed during one week after the second injection. RESULTS: All 5 patients with MTC showed positive immunoscintigraphy (IS). In the smallest visualized and resected tumor (0.8 g), the fraction of injected activity per gram (% ID/g) was 0.1% at Day 3. IS was positive in 4 of the 5 patients with SCLC. The volume of the smallest visualized SCLC tumor was estimated at 11 +/- 2 ml, and tumor uptake was about 0.009% ID/g. Tumor dose estimates ranged from 4.2 to 174 cGy/mCi in patients with MTC and from 1.7 to 8 cGy/mCi in patients with SCLC. CONCLUSION: High absorbed dose values were calculated for small MTC recurrences. For SCLC recurrences the values were smaller but in the same range as those obtained by other investigators with the one-step technique in lymphoma.

Antibodies, Bispecific↗
PubMed1998

Beta-2-glycoprotein I dependent lupus anticoagulants form stable bivalent antibody beta-2-glycoprotein I complexes on phospholipid surfaces.

The precise mechanism by which Beta-2-glycoprotein I (beta2-GPI-) dependent lupus anticoagulants lengthen phospholipid-dependent clotting reactions is still poorly understood. In order to study this, murine monoclonal antibodies (moabs) against human beta2GPI were raised. Eight of the 21 anti-beta2GPI moabs, obtained from 2 fusions, fulfilled the criteria for lupus anticoagulant (LA) activity as tested with a variety of sensitive screening assays and confirmatory tests. Seven moabs did not influence any clotting test. The LA positive moabs were found to compete for similar or closely spaced epitopes on immobilized beta2GPI. Two moabs with potent LA activity (moabs 22 F 6 and 22 B 3) and 1 moab without LA activity (moab 16 B 3) were selected to study the interaction between antibody, beta2GPI and phospholipid. Interactions were investigated by real-time biospecific interaction analysis (BIA) based on plasmon surface resonance technology on a BIA-core instrument using a sensor chip coated with phospholipid. When 22 F 6, the moab with the most pronounced LA activity, was allowed to interact with the phospholipid surface at concentrations between 0 and 400 nmol/l, no appreciable binding could be detected. Likewise, no binding could be measured when beta2GPI at concentrations between 0 and 400 nmol/l was passed over the phospholipid coated sensor chip. Combinations of beta2GPI and 22 F 6 resulted in significant binding. Similar results were obtained with 22 B 3, another moab with LA activity. A LA negative Moab, 16 B 3, did not cause binding of antibody-beta2GPI complexes. Fab' fragments, derived from moab 22 F 6, inhibited the binding of beta2GPI-22 F 6 and beta2GPI-22 B 3 in a concentration dependent way, indicating that only bivalent beta2GPI-antibody complexes bind with high affinity to phospholipids. Fab' fragments, derived from moab 22 F 6, also inhibited the LA effect of moabs 22 F 6 and 22 B 3 in diluted plasma. In summary, these experiments indicate that the beta2GPI-dependent LA effect depends on the formation of bivalent beta2GPI-antibody complexes on phospholipid surfaces.

Antibodies, Bispecific↗
PubMed1998

Radioimmunodetection of medullary thyroid carcinoma using indium-111 bivalent hapten and anti-CEA x anti-DTPA-indium bispecific antibody.

UNLABELLED: Pretargeting labeled bivalent hapten with bispecific antibodies has proven feasible in the clinic, and our earlier results have suggested the technique may be very sensitive for detecting small recurrences and metastases. Medullary thyroid carcinoma (MTC) is an example where this technique may be the most useful since local recurrences and isolated metastases are removed surgically when detected, and thyrocalcitonin provides a specific and sensitive tumor marker. In our current study, we evaluated pretargeted immunoscintigraphy in a larger number of MTC patients. METHODS: Anti-carcinoembryonic antigen (CEA) x anti-diethylenetriaminepentaacetic acid (DTPA) indium bispecific antibody and 111In-labeled bivalent DTPA hapten were administered sequentially (4-5 days apart) to 44 patients with elevated circulating calcitonin after resection of primary MTC. Immunoscintigraphy was performed 2, 5 and 24 hr after hapten injection and, when necessary, at longer time intervals. When available, a handheld gamma probe was used during surgery. RESULTS: Fifteen patients had known tumor sites before immunoscintigraphy. Tumors were imaged in 12 (80%) of these patients, including 3 with liver metastases. Five unknown tumor sites were detected. For the 29 patients with occult disease, immunoscintigraphy detected high-activity uptake sites in 21 patients (72%), including 5 in the liver. Twelve were confirmed by surgery, 1 by guided morphologic imaging and 1 by venous catheterization. There were 2 false-positive patients. The other 5 patients have not yet been confirmed. All detected liver metastases were high-activity uptake areas. Radioimmunoguided surgery was used in 14 patients. It was considered helpful by the surgeon in 12 patients, including 4 patients where it determined the resection of small, not palpable nor visible, tumor-involved lymph nodes. Surgical resection resulted in a significant decrease (8 patients) or normalization (1 patient) of circulating calcitonin and CEA. CONCLUSION: This technique affords high sensitivity and specificity for detecting small tumor lesions including liver metastases. Its use for immunoscintigraphy and guided surgery should improve the therapeutic management of recurrent MTC.

Adult↗
PubMed2025

Structure-informed theoretical modeling defines principles governing avidity in bivalent protein interactions.

In signaling cascades, where domain-motif interactions tend to interact with relatively low affinity (allowing for reversibility), signaling proteins often encode multiple domains or motifs, which present the possibility of avidity - drastically increasing the interaction strength and duration as a result of multivalent binding. However, given the large combinatorial space, predicting and validating multivalent interactions that interact with avidity is a challenge. Here, we integrate mechanistic modeling, structure-based analysis, and experimental approaches as a framework for defining the conditions under which avidity plays a role. We explore the tandem SH2 domain family of interactions with bisphosphorylated partners as a multivalent archetype, which encompasses key secondary messengers in tyrosine kinase signaling networks. While certain multivalent interactions have been shown to be necessary in immune receptor recruitment of partners, bivalent recruitment of tandem SH2 domains more broadly is poorly understood. Theoretical modeling suggests that maximum avidity occurs with closely spaced or flexibly linked phosphotyrosine sites, combined with moderate monovalent affinities - exactly around the innate range of SH2 domain affinity. Surprisingly, despite sequence diversity, structure-based analysis showed remarkably conserved three-dimensional spacing between SH2 domains across all tandem SH2 families, which we corroborate experimentally, suggesting evolutionary optimization for avidity interactions. The combination of structure-based analysis of domain spacing with available monovalent experimental data appears to be sufficiently accurate to predict and rank order high affinity interactions of tandem SH2 domain recruitment to the EGFR C-terminal tail. These approaches lay the groundwork for larger utility in multivalent prediction and testing to help better understand protein interactions that drive cell signaling.

BLI↗
PubMed2025

Bivalent RSV Prefusion F Protein-Based Vaccine for Preventing Cardiovascular Hospitalizations in Older Adults: A Prespecified Analysis of the DAN-RSV Trial.

IMPORTANCE: Respiratory syncytial virus (RSV) infection is linked to elevated cardiovascular risk, particularly in individuals with preexisting cardiovascular disease (CVD). A bivalent RSV prefusion F protein (RSVpreF) vaccine was recently approved for preventing RSV-related lower respiratory tract illness, but its effectiveness against cardiovascular outcomes has not been evaluated in a randomized trial. OBJECTIVE: To investigate the vaccine effectiveness of RSVpreF compared with no vaccine against cardiovascular outcomes among adults aged 60 years or older. DESIGN, SETTING, AND PARTICIPANTS: Prespecified secondary analysis of the DAN-RSV trial, a pragmatic, open-label, individually randomized clinical trial conducted in Denmark during the 2024-2025 winter season. The first participant was enrolled on November 18, 2024. Adults aged 60 years or older were eligible for inclusion regardless of comorbidity status. INTERVENTIONS: Participants were randomized 1:1 to receive RSVpreF (n = 65 642) or no vaccine (n = 65 634). MAIN OUTCOMES AND MEASURES: Hospitalization for any cardiorespiratory disease was a prespecified secondary outcome, and hospitalizations for any CVD, heart failure, myocardial infarction, stroke, and atrial fibrillation were prespecified exploratory outcomes. Outcomes were assessed from 14 days after booked study visit through May 31, 2025. Vaccine effectiveness was calculated as 1 - incidence rate ratio, expressed as a percentage. RESULTS: Of 131 276 participants included (mean age, 69.4 [SD, 6.5] years; 50.3% male), 28 662 (21.8%) had preexisting CVD. All-cause cardiorespiratory hospitalization incidence was lower in the RSVpreF group compared with the control group (26.3 vs 29.2 events per 1000 participant-years [PY]; absolute rate reduction, 2.90 [95% CI, 0.10-5.71] per 1000 PY; vaccine effectiveness, 9.9% [95% CI, 0.3%-18.7%]; P = .04). There was no significant interaction by baseline CVD status (CVD at baseline: vaccine effectiveness, 5.0% [95% CI, -11.2% to 16.7%]; no CVD at baseline: vaccine effectiveness, 15.2% [95% CI, 2.2%-27.1%]; P = .27 for interaction). For the RSVpreF group vs control group, respectively, incidence rates of all-cause cardiovascular hospitalization were 16.4 vs 17.7 events per 1000 PY (vaccine effectiveness, 7.4% [95% CI, -5.5% to 18.8%]; P = .24), and incidence rates of stroke were 3.0 vs 3.8 events per 1000 PY (vaccine effectiveness, 19.4% [95% CI, -8.6% to 40.4%]; P = .14). There were also no statistically significant between-group differences for myocardial infarction, heart failure hospitalization, and atrial fibrillation. CONCLUSIONS AND RELEVANCE: In adults aged 60 years or older, all-cause cardiorespiratory hospitalization was significantly lower with RSVpreF than with no vaccine. The findings suggest potential downstream cardiorespiratory benefits of RSV immunization, although the effect on all-cause cardiovascular hospitalization was not statistically significant. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT06684743.

Aged↗
PubMed1996

A bivalent single-chain antibody-toxin specific for ErbB-2 and the EGF receptor.

ErbB-2 and EGF receptors are often co-expressed in human tumors and have been shown to synergize in the transformation of cells in experimental model systems. Transactivation of ErbB-2 can occur via ligand-induced heterodimerization with EGF receptor or other members of the ErbB family of receptor tyrosine kinases. We have previously described the potent anti-tumoral activity of the monospecific single-chain antibody-toxins scFv(FRP5)-ETA and scFv(225)-ETA binding to, respectively, ErbB-2 and the EGF receptor. Here we report the construction and functional characterization of a novel bivalent, bispecific single-chain antibody-toxin, scFv2(FRP5/225)-ETA. The fusion protein consists of 2 scFv domains specific for ErbB-2 and the EGF receptor linked to a modified Pseudomonas exotoxin A. ScFv2(FRP5/225)-ETA displayed in vitro cell killing activity on tumor cells overexpressing either ErbB-2 or the EGF receptor similar to that of the monospecific toxins. It was more potent in vitro and in vivo in inhibiting the growth of tumor cells expressing both receptors. Treatment of A431 cells with scFv2(FRP5/225)-ETA led to an increase in EGF receptor and ErbB-2 phosphotyrosine content, most likely via the induction of receptor heterodimers. This may explain the enhanced toxicity of the bispecific antibody-toxin.

ADP Ribose Transferases↗
PubMed1996

A systematic analysis of average molecular weights and gelation conditions for branched immune complexes: the interaction between a multivalent antigen with distinct epitopes and many different types of bivalent antibodies.

A systematic model, based on standard equilibrium expressions and probability theory, is presented to calculate average molecular weights and gelation conditions for the immune system consisting of a single type of antigens with three (or more) different epitopes and three (or more) types of bivalent antibodies. Molecular weights Mn, Mw, Mz, and any other higher average molecular weights of formed branched antigen-antibody complexes in such an immune system are calculated directly without determining the whole distribution. The conditions for the formation of gel complexes also can be determined by this model.

Antibodies, Bispecific↗
PubMed2000

Synthesis of bivalent inhibitors of eucaryotic proteasomes.

Based on the peculiar spatial array of the active sites in the internal chamber of the multicatalytic proteasome, as derived from the X-ray structure of yeast proteasome, homo- and heterobivalent inhibitors were designed and synthesized to exploit the principle of multivalency for enhancing inhibition potency. Peptidic bis-aldehyde compounds of the octapeptide size were synthesized to address adjacent active sites, whilst a PEG spacer with a statistical length distribution of 19-25 monomers was used to link two identical or different tripeptide aldehydes as binding heads. These bis-aldehyde compounds were synthesized applying both methods in solution and solid phase peptide synthesis. Bivalent binding was observed only for the PEG-spaced inhibitors suggesting that binding from the primed side prevents hemiacetal formation with the active site threonine residue.

Chymases↗