Relative fitness of three organophosphate-resistant strains of Culex pipiens pallens (Diptera: Culicidae)

Effects of dipterex, temephos, and chlorpyrifos resistance on the relative fitness of Culex pipiens pallens (L.) were evaluated by examining developmental and reproductive characteristics. Age-specific life tables of Dip-R- (dipterex), Tmo-R- (temephos), and Chl-R- (chlorpyrifos) resistant strains were compared with the susceptible strain to determine relative fitness based on population trend indices (I). The 3 organophosphate-resistant strains possessed reproductive and developmental disadvantages involving fecundity and survival relative compared with the susceptible strain, with relative fitness values of 0.465, 0.520, and 0.501, respectively. These results are discussed in relation to the reversal from resistance to susceptibility in natural populations of mosquitoes.

Chronic intermittent ethanol exposure selectively alters the expression of Gα subunit isoforms and RGS subtypes in rat prefrontal cortex

Chronic alcohol exposure induces pronounced changes in GPCR-mediated G-protein signaling. Recent microarray and RNA-seq analyses suggest associations between alcohol abuse and the expression of genes involved in G-protein signaling. The activity of G-proteins (e.g. Gαi/o and Gαq) is negatively modulated by regulator of G-protein signaling (RGS) proteins which are implicated in drugs of abuse including alcohol. The present study used 7days of chronic intermittent ethanol exposure followed by 24h withdrawal (CIE) to investigate changes in mRNA and protein levels of G-protein subunit isoforms and RGS protein subtypes in rat prefrontal cortex, a region associated with cognitive deficit attributed to excessive alcohol drinking. We found that this ethanol paradigm induced differential expression of Gα subunits and RGS subtypes. For example, there were increased mRNA and protein levels of Gαi1/3 subunits and no changes in the expression of Gαs and Gαq subunits in ethanol-treated animals. Moreover, CIE increased the mRNA but not the protein levels of Gαo. Additionally, a modest increase in Gαi2 mRNA level by CIE was accompanied by a pronounced increase in its protein level. Interestingly, we found that CIE increased mRNA and protein levels of RGS2, RGS4, RGS7 and RGS19 but had no effect on the expression of RGS5, RGS6, RGS8, RGS12 or RGS17. Changes in the expression of Gα subunits and RGS subtypes could contribute to the functional alterations of certain GPCRs following chronic ethanol exposure. The present study suggests that RGS proteins may be potential new targets for intervention of alcohol abuse via modification of Gα-mediated GPCR function.

Optimized plan of centralized and decentralized wastewater reuse systems for housing development in the urban area of Xi'an, China

In an arid and water deficient urban area, such as Xi'an in the northwest region of China, gardening and forestation often use large amounts of tap water. Therefore, there is a need for treated wastewater reuse for such purpose to mitigate urban water shortage, especially in the newly developed housing area, where a high green coverage is often required for both commercial value and living condition improvement. Supply of the treated wastewater through a centralized system which has been planned and partially constructed is one measure to meet such need, but it may require an extension of the distribution system for a full coverage of the whole city area. A supplementary measure is to construct decentralized wastewater treatment and reuse (DESAR) systems in areas that are distant from the planned centralized system. In order to optimize the plan of wastewater reuse for housing development in the urban area, the authors analyzed the existing plan of centralized wastewater reuse and the envisaged plan of housing development in Xi'an urban area. A method was proposed for selection of a feasible way of reclaimed water reuse from two options, namely centralized and decentralized ones, by introducing a critical distance L0 which depends on the relationship between the cost for DESAR system installation and that for water delivery pipeline construction. If the distance from the project site to the nearest access point of the centralized system L is shorter than L0 then using reclaim water from the centralized system becomes more feasible, and otherwise DESAR system installation becomes more feasible. A distribution map was thus obtained to show an optimized plan of centralized and decentralized wastewater reuse systems for housing development in Xi'an city. An example was also given to show the advantage of a DESAR system installed.

Pemetrexed (P) in relapsed small cell lung cancer (SCLC): Preliminary results of a phase II trial

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Background: Pts with relapsed SCLC have a poor prognosis and few effective treatment options. P is a novel multitargeted antifolate that is active and well-tolerated as a single agent in lung cancer. We undertook a trial to assess the efficacy and safety of single- agent P in both chemosensitive (S) and chemorefractory (R) relapsed SCLC pts. Methods: Eligible pts had limited or extensive- stage SCLC, PS 0 to 2, and only 1 prior chemo regimen. S pts were defined as having had a prior response with disease progression >2 mos from end of 1st-line chemo. R pts were those who progressed while on 1st-line therapy, or had any response but progression <2 mos from end of 1st-line chemo. The initial P dose tested was 500 mg/m2 q 21 d. Planned sample sizes were 36 S pts in a 2-stage sequential fashion with potential early stopping for lack of efficacy or unacceptable toxicity, and 25 R pts in a single-stage design with no stopping rule. The stopping rule was invoked when <3 of 14 qualified S pts responded. The protocol was then amended to evaluate P at 900 mg/m2 in additional cohorts of 40 S and 40 R pts. Pts were to receive folic acid and Vitamin B12 prior to treatment with P. The primary outcome measure was response rate. Results: From 7/04 to 3/06, 121 pts were enrolled, with 116 pts treated. S and R pts were analyzed separately at both dose levels. S pts (n=56): M/F, 29/27; median age 65 (range 43–82); PS 0/1/2, 25/23/8. R pts (n=65): M/F, 31/34; median age 64 (range, 35–85); PS 0/1/2, 16/37/12. *3 S pts treated with P 900 mg/m2 remain with disease control after a minimum of 11 mos of follow-up. Conclusions: Preliminary clinical benefit rates (CR+PR+SD) of 20% and 17.4% achieved respectively in S and R pts treated with P 500 mg/m2 suggest modest activity of single-agent P in relapsed SCLC. P can be given at a dose of 900 mg/m2 without a significant increase in Grades 3–4 toxicities, although this does not appear to increase efficacy.

[Table: see text] [Table: see text]

Active immunization against AMH reveals its inhibitory role in the development of pre-ovulatory follicles in Zhedong White geese

The aim of this study was to investigate the effects of active immunization against recombinant Anti-Müllerian hormone (AMH) protein on the ovarian follicular development, egg production, and molecular regulatory mechanisms in broody-prone Zhedong White geese. For this, a recombinant goose AMH protein was expressed using a prokaryotic expression system. Fifty incubating geese from the same genetic background were selected and equally divided into two groups. The immunization group was actively immunized against the recombinant goose AMH protein, whereas the control group was immunized against bovine serum albumin (BSA). Immunization against AMH accelerated ovarian follicular development and increased clutch sizes by one to two eggs in two consecutive laying-incubation cycles. Furthermore, immunization against AMH upregulated the mRNA transcription levels of the FSH-beta gene in the pituitary gland, and FSHR, 3beta-HSD, and Smad4 genes in the granulosa layer of pre-ovulatory follicles; however, immunization downregulated the expression of the OCLN gene in the granulosa layer of pre-ovulatory follicles, and Smad5 and Smad9 genes in the granulosa layer of SYFs. These results suggest that AMH might hinder ovarian follicular development by decreasing both pituitary FSH secretion as well as ovarian follicular sensitivity to FSH. The latter molecular mechanism could be fulfilled by regulating Smad5 or Smad9 signals in SYFs, as well as the FSHR and Smad4 signals that affect progesterone synthesis and yolk deposition in the pre-ovulatory follicles.

A 9-year experience study of single-port micro-laparoscopic repair of pediatric inguinal hernia using a simple needle

Purpose

As laparoscopic techniques and equipments improve, laparoscopic inguinal hernia repair has been gaining popularity. The objective of the study was to summarize 9 years of experience using a single-port micro-laparoscopic approach to repair pediatric inguinal hernias with a simple hernia needle.

Methods

1880 children with inguinal hernias were enrolled using micro-laparoscopic surgery between June 2009 and 2018. All patients underwent high ligation surgery using a single-port micro-laparoscopic technique. The clinical data were retrospectively analyzed.

Results

All micro-laparoscopic surgeries were successfully performed in the 1880 patients, who ranged in age from 2 months to 14 years (3.66 ± 2.96 years) including 1622 males and 258 females. Among them, 1299 cases were unilateral hernias and 581 cases were bilateral hernias. The average operating time was 12.5 ± 3.5 min for a unilateral hernia and 20.5 ± 4.5 min for bilateral hernias. All patients were discharged 1–2 days after surgery, and the average length of their hospital stay was 2–4 days. Complications of knot reaction and pneumoscrotum occurred in 5 cases (0.27%) and 54 cases (2.87%), respectively, but these cases were properly managed, with no major impact on the operational outcomes. All patients were followed up for 3–65 months; there were 13 recurrent cases (0.69%).

Conclusions

Single-port micro-laparoscopic herniorrhaphy in children using a simple hernia needle is a reliable and minimally invasive procedure.

Luminescence of CsGd2F7 crystals

Optical and dosimetric properties of nominally pure CsGd2F7 crystals and of CsGd2F7 crystals doped with various concentrations of Pr3+ ions were investigated. Effects of X, beta and UV irradiation on these crystals were studied. Methods of optical absorption, X and UV excited luminescence, thermoluminescence (TL), phototransferred thermoluminescence and optically stimulated luminescence were used in these investigations. The dependence of the TL efficiency on the radiation dose was found to be linear up to 6 kGy for the 3 at.% Pr3+ doped samples. The crystals containing from 0.3 at.% to 1.0 at.% of Pr3+ ions were found to have the best TL sensitivity and the intensity of the main TL peak in these samples was more than two orders of magnitude higher than that of the pure crystals. The TL sensitivity of the CsGd,F7:Pr3+ crystals was also compared with that of other commonly used TLD materials.

Imaging study of the long extracranial extension of the inferior petrosal sinus with MSCT

The aim of this study was to explore the anatomic route of Long-Inferior Petrosal Sinuses (IPS) with multi-slice spiral computed tomography, and to provide referenced evidence for the interventional preoperative evaluation for the diagnosis and treatment of skull base and sellar lesions. The route of Long-IPS and its confluence with the internal jugular vein (IJV) and the connection level of 12 IPS were shown with multi-planar reconstruction and curved multi-planar reconstruction, and the IPS length was determined. Combining the results of continuous multi-slice scanning, the diameters of the IPS at the initial segment in the jugular foreman and middle segment and the confluence segment of the IPS-IJV junction level were determined. The mean length of the Long-IPS was 66.2 +/- 17.5 mm, and the length was over 60 mm on eight sides and its peak value 100 mm. The mean diameters of the IPS were 2.4 mm +/- 0.7 mm, 2.1 mm +/- 0.4 mm, and 2.1 mm +/- 0.5 mm at the initial, middle, and confluent segments, respectively. Their diameters were equal to or greater than 2 mm at the connection level on eight sides. Furthermore, the diameter was greater than 1.6 mm at the middle and initial segments. The Long-IPS might be used as a route to the intra-cranial IPS. MSCT is helpful for showing the route and variation of the IPS and could be an effective method for preoperative evaluation of the IPS.

New edge coherent mode providing continuous transport in long-pulse H-mode plasmas

An electrostatic coherent mode near the electron diamagnetic frequency (20-90 kHz) is observed in the steep-gradient pedestal region of long pulse H-mode plasmas in the Experimental Advanced Superconducting Tokamak, using a newly developed dual gas-puff-imaging system and diamond-coated reciprocating probes. The mode propagates in the electron diamagnetic direction in the plasma frame with poloidal wavelength of ∼8  cm. The mode drives a significant outflow of particles and heat as measured directly with the probes, thus greatly facilitating long pulse H-mode sustainment. This mode shows the nature of dissipative trapped electron mode, as evidenced by gyrokinetic turbulence simulations.

Recombinant Treponema pallidum protein Tp47 promoted the phagocytosis of macrophages by activating NLRP3 inflammasome induced by PKM2-dependent glycolysis

BACKGROUND

Glycolysis is a critical pathway in cellular glucose metabolism that provides energy and participates in immune responses. However, whether glycolysis is involved in NOD-like receptor family protein 3 (NLRP3) inflammasome activation and phagocytosis of macrophages in response to Treponema pallidum infection remains unclear.

OBJECTIVES

To investigate the role of glycolysis in activating the NLRP3 inflammasome for regulating phagocytosis in macrophages in response to T. pallidum protein Tp47 and its associated mechanisms.

METHODS

Interactions between activation of the NLRP3 inflammasome and phagocytosis and the role of glycolysis in Tp47-treated macrophages were investigated through experiments on peritoneal macrophages and human monocytic cell line-derived macrophages.

RESULTS

Activation of phagocytosis and NLRP3 inflammasome were observed in Tp47-treated macrophages. Treatment with NLRP3 inhibitor MCC950 or si-NLRP3 attenuated Tp47-induced phagocytosis. Glycolysis and glycolytic capacity were enhanced by Tp47 stimulation in macrophages, and a change in the levels of glycolytic metabolites (phosphoenolpyruvate, citrate and lactate) was induced by Tp47 in macrophages. Inhibition of glycolysis with 2-deoxy-D-glucose, a glycolysis inhibitor, decreased the activation of NLRP3. Expression of M2 isoform of pyruvate kinase (PKM2), an enzyme catalysing a rate-limiting reaction in the glycolytic pathway, was upregulated in Tp47-stimulated macrophages. Inhibition of PKM2 with shikonin or si-PKM2 decreased glycolysis and NLRP3 activation.

CONCLUSION

Tp47 promotes phagocytosis in macrophages by activating the NLRP3 inflammasome, which is induced by the enhancement of PKM2-dependent glycolysis.

Exploratory analysis as a sequel to suspected increased rate of cancer in a small residential or workplace community

A suspicion that the incidence of cancer is rising in a residential or workplace community is often a cause of alarm among members of that community. The seemingly excessive number of diagnoses encountered may he due to: (i) a known explanatory variable, such as ageing of the community members; (ii) random occurrence of an event which is rare under stable conditions; (iii) exposure to an undefined carcinogenic agent. An exploratory analysis is suggested in order to consider the support indicated by the data with respect to each of the two last possibilities while controlling the first. The analysis involves several procedures which differ with respect to the targeted temporal pattern of the diagnoses. These procedures are mainly based on the a priori probability that a diagnosis is made within the time interval observed between consecutive diagnoses. When the number of diagnoses is found to be excessively large, the temporal pattern of the diagnoses may indicate whether the event is likely to be an incidental occurrence or due to the effect of a carcinogen.

Evaluation of the semen swim-up method for bovine sperm RNA extraction

Isolation of high-quality RNA is important for assessing sperm gene expression, and semen purification methods may affect the integrity of the isolated RNA. This study evaluated the effectiveness of the sperm swim-up method for seminal RNA isolation. Frozen semen samples in straws from three bulls of proven fertility were purified by the swim-up method. RNA extraction was carried out using the E.Z.N.A.(TM) Total RNA kit II, with non-swim-up sperm as a control. Total sperm RNA was analyzed by UV spectrophotometry, reverse transcription polymerase chain reaction (RT-PCR), and agarose gel electrophoresis, and expression of the sex-determining region on the Y chromosome (SRY), leptin (LEP), and ribosomal protein subunit 23 (RPS23) genes, were determined. 18S RNA was used as a positive control. Fewer somatic cells were found in sperm swim-up samples than in the non-swim-up counterparts (0 x 10(3) vs 17.33 ± 2.52 x 10(3) sperm, P < 0.05). In addition, high-quality RNA was obtained in about 2 h, with no significant difference between groups. Interestingly, the yields of RNA fragments containing ≥200 nucleotides were significantly reduced in sperm swim-up samples (0.92 ± 0.41 x 10(7) sperm) compared with the non-swim-up samples (1.36 ± 0.33 x 10(7) sperm, P < 0.05). After RT-PCR, clear bands representing SRY, LEP, and RPS23 in sperm cDNA were observed on agarose gel electrophoresis. Finally, no bands corresponding to 18S RNA were found in RNA samples from the sperm swim-up group. Our findings suggest that small amounts of sperm RNA can be efficiently extracted from frozen straw semen samples using the swim-up technique.

Setting the new FRAX reference threshold without bone mineral density in Chinese postmenopausal women

PURPOSE

Despite the large number of osteoporosis patients in China, the diagnosis and treatment rates remain low. The Fracture Risk Assessment Tool (FRAX) can be used to effectively evaluate fracture risk. In this study, we explored the Chinese-specific thresholds of FRAX without the T-score.

METHODS

In all, 264 postmenopausal women aged > 50 years were randomly recruited from community-medical centers. All subjects completed self-reported questionnaires, BMD measurements, and spinal radiographs. The 10-year hip and major osteoporotic fracture risks were calculated by FRAX. A new threshold for both 10-year hip and major osteoporotic fracture risk was explored with receiver operating characteristic (ROC) curve analysis.

RESULTS

Overall, 92 subjects were diagnosed with osteoporosis. Among them, 14 participants with T-score > - 2.5 were diagnosed with osteoporosis based on clinical fractures. ROC analysis showed the cut-off value of the 10-year hip osteoporotic fracture for detecting osteoporosis was 0.95%, while that of 10-year major osteoporotic fracture was 4.95%. The sensitivity and specificity of the 10-year hip osteoporotic fracture probability for detecting osteoporosis were 0.86 and 0.59, respectively, while the guideline-recommended threshold had a sensitivity of 0.49 and specificity of 0.83. The sensitivity and specificity of the 10-year major osteoporotic fractures with the new threshold were 0.76 and 0.69, respectively, while the recommended threshold had a sensitivity of 0 and specificity of 1.

CONCLUSION

Current guideline-recommended FRAX thresholds without BMD showed low sensitivity. Therefore, 10-year osteoporotic hip fracture probability ≥ 0.95% and 10-year osteoporotic major fracture probability ≥ 4.95% are recommended as the new thresholds.

Cloning of murine glycosyl phosphatidylinositol anchor attachment protein, GPAA1

Glycosyl phosphatidylinositols (GPIs) are used to anchor many proteins to the cell surface membrane and are utilized in all eukaryotic cells. GPI anchoring units are attached to proteins via a transamidase reaction mediated by a GPI transamidase complex. We isolated one of the components of this complex, mGPAA1 (murine GPI anchor attachment), by the signal sequence trap method. mGPAA1 cDNA is about 2 kb in length and encodes a putative 621 amino acid protein. The mGPAA1 gene has 12 small exons and 11 small introns. mGPAA1 mRNA is ubiquitously expressed in mammalian cells, and in situ hybridization analysis revealed that it is abundant in the choroid plexus, skeletal muscle, osteoblasts of rib, and occipital bone in mouse embryos. Its expression levels and transamidation efficiency decreased with differentiation of embryonic stem cells. The 3T3 cell lines expressing antisense mGPAA1 failed to express GPI-anchored proteins on the cell surface membrane.

Rate dependence of mechanically induced electrophysiological changes in right ventricle of anaesthetized lambs during pulmonary artery occlusion

AIM

Mechanically induced early afterdepolarization (EAD) is morphologically similar but different in the mechanisms with drug-induced EAD, which lead to arrhythmia. Pacing suppresses the drug-induced EAD and arrhythmia, however the effect of pacing on mechanically induced EAD and arrhythmia is not clear. This study addressed this issue in right ventricle (RV) of anaesthetized lambs.

METHODS

Six lambs were anaesthetized, and their hearts exposed. Nine monophasic action potential (MAP) electrodes were placed on RV apex, outflow and inflow regions, and recorded before, during, and after a 10 s occlusion of pulmonary artery at a number of pacing rates.

RESULTS

Pacing significantly reduced the baseline MAP duration at 90% repolarization (MAPD90), decreased the reduction of MAPD at early repolarization at the peak of occlusion. Nonetheless, the percentage of reduction was not significantly different among them. Pacing was able to reduce the frequencies, size of mechanically induced EADs. MAPD90 at the peak of occlusion was all shortened during pacing rather than some lengthened at intrinsic rate. Therefore, the dispersion of MAPD90 at the peak of occlusion reduced from 86 +/- 6 ms at intrinsic rate to 42 +/- 4 ms at 120 beats min-1, 38 +/- 3 ms at 150 beats min-1 and 26 +/- 3 ms at 170 beats min-1. Ultimately, pacing reduced/suppressed mechanically induced premature ventricular beats. These alterations were inversely related to heart rates.

CONCLUSION

Pacing reduces/suppresses both stretch-induced EADs and arrhythmia. These modulations are remarkably similar to those on other EADs by the pacing.

Improved Constraints on Sterile Neutrino Mixing from Disappearance Searches in the MINOS, MINOS+, Daya Bay, and Bugey-3 Experiments

Searches for electron antineutrino, muon neutrino, and muon antineutrino disappearance driven by sterile neutrino mixing have been carried out by the Daya Bay and MINOS+ collaborations. This Letter presents the combined results of these searches, along with exclusion results from the Bugey-3 reactor experiment, framed in a minimally extended four-neutrino scenario. Significantly improved constraints on the θ_{μe} mixing angle are derived that constitute the most constraining limits to date over five orders of magnitude in the mass-squared splitting Δm_{41}^{2}, excluding the 90% C.L. sterile-neutrino parameter space allowed by the LSND and MiniBooNE observations at 90% CL_{s} for Δm_{41}^{2}<13  eV^{2}. Furthermore, the LSND and MiniBooNE 99% C.L. allowed regions are excluded at 99% CL_{s} for Δm_{41}^{2}<1.6 eV^{2}.

Association of Pulsatility Index in the Middle Cerebral Artery with Intelligence Quotient in Children with Sickle Cell Disease

The aim of this study was to explore whether intellectual performance in children with Sickle Cell Disease and with low risk of stroke as determined with conventional transcranial Doppler ultrasonography (TCD) criteria was associated with hemodynamic parameters in imaging TCD, when controlling for hematological and socio-economical variables and presence of silent infarcts. We performed neuropsychological testing with Kaufman Brief Intelligence Test (K-BIT-IQ) and imaging TCD examinations to measure blood flow velocities and pulsatility indexes (PI) in the middle cerebral arteries (MCA) In 46 children with homozygous HbSS (mean age 108±34 months, range limits: 47–166 months; 24 females), without a history of stroke or transient ischemic attack, with no stenosis on magnetic resonance angiography and with velocities below 170 cm/s in screening conventional TCD. Mean K-BIT IQ Composite and Vocabulary scores (91±13 and 86±14 respectively) were significantly below the average scores of 100 for the age-matched population (one sample t-test=5.21, p<0.001). Using univariate and multivariate regression models, we found that lower PI in the right MCA was associated with lower K-BIT-IQ Composite and Vocabulary scores. Furthermore, we found that interhemispheric differences in PIs were even more strongly associated with neuropsychological performance, whereas flow velocities were not associated with the K-BIT-IQ score. Using a model of chronic anemia, we found that cognitive functioning was associated with cerebral hemodynamics.

Studies of human motor physiology with transcranial magnetic stimulation

Transcranial magnetic stimulation (TMS) is a safe, noninvasive, and painless way to stimulate the human motor cortex in behaving human subjects. When it is applied as a single-pulse, measurements such as central conduction time, motor threshold, silent-period duration, recruitment curve, and mapping of muscle representation can be determined. Paired-pulse TMS is a useful way to examine cortical excitability. Single and paired-pulse TMS have been applied to study plasticity following amputation and cortical excitability in patients with dystonia. Another form of TMS is repetitive TMS (rTMS), with stimuli delivered repeatedly to a single scalp site. High-frequency rTMS can be used to transiently inactivate different cortical areas to study their functions. rTMS can also modulate cortical excitability. At stimulus frequencies higher than 5 Hz, rTMS increases cortical excitability, and stimulation around 1 Hz reduces cortical excitability. Modulation of cortical excitability by rTMS has therapeutic potential in psychiatric and neurological disorders.

Characterization of l-asparaginase fused with a protective ScFv and the protection mechanism

A fusion protein of the protective scFv linked to the C-terminus of ASNase via (Gly(4)Ser)(6) peptide was constructed. The ASNase-scFv fusion protein expressed in Escherichia coli exists mainly in the form of inclusion bodies, and a small amount of it was soluble. The soluble form was purified by four-step purification and it has been demonstrated that ASNase-scFv fusion exists as a dimer. By assay of the stability against proteolysis, the ASNase-scFv fusion was found to be more stable than native ASNase but less stable than scFv-ASNase fusion. The results of immunological assay indicated that the immunogenicity of the fusion proteins increased while their binding capacity with the anti-ASNase serum decreased by comparison to the native ASNase. Moreover, here the comparison of the basic physical and chemical properties of the ASNase-scFv fusion, scFv-ASNase fusion, and native ASNase is presented. Based on the structural evidence and the biochemical analysis described in this paper, the protection mechanism proposed in our previous study was further supported. The scFv moiety of the fusion protein may confer the ASNase moiety resistance to proteolysis as a result of both steric hindrance such as blocking the cleavage sites of trypsin and a change in the electrostatic potential surface of the enzyme.