Down-regulation of specific antigen-driven cytokine production in a population with endemic Schistosoma japonicum infection

Schistosome antigen-driven cytokine responses and antischistosome antibody levels of residents of a Schistosoma japonicum endemic island in Poyang Lake, Jiangxi Province were studied before and 45 days after treatment with praziquantel. IL-4, IL-5, IL-10 and INF-gamma were all detected in the supernatants of whole-blood cultures after stimulation with schistosome soluble egg antigen (SEA) and soluble worm antigen preparation (SWAP). The percentages of subjects producing detectable amounts of each cytokine assayed were higher in the group who were negative by stool examination at the start of the study than in those who were initially stool positive. After praziquantel treatment the percentages of subjects producing both type I and type II cytokines increased. This suggests that the production of both types of cytokine was down-regulated in the presence of live, egg-laying S. japonicum adult worms but that this was reversible by treatment. In contrast, the antibody studies showed higher levels of SWAP and SEA-specific antibodies (IgE, total IgG, IgG4, IgM) in subjects who were originally stool-positive than in those who were stool-negative. After treatment specific IgE responses were elevated, but total IgG and IgG4 anti-SEA and IgM anti-SWAP antibody levels all fell significantly.

Characterization of some mesogenic alkyl 1-thioglycosides

A series of dodecyl 1-thio-β-D-glycosides has been synthesized and characterized (DSC, NMR, CP MAS, X-ray diffraction) as possible new marking materials with liquid-crystalline properties. These compounds undergo solid to liquid crystal phase transitions at various temperatures, which depend on the nature of the carbohydrate part of the structure. Their liquid-crystalline phases show extreme shear thinning behaviour.Key words: liquid crystal, powder X-ray diffraction, phase transition, thioglycoside, solid-state NMR, marking material

Subcellular distribution of cadmium and its cellular ligands in mussel digestive gland cells as revealed by combined autometallography and X-ray microprobe analysis

Autometallography (AMG) and electron probe X-ray microanalysis (EPXMA) were applied in combination to determine the subcellular distribution of Cd and its subcellular ligands in the digestive gland cells of Cd-exposed mussels Mytilus galloprovincialis. Black silver deposits (BSD), which reveal the presence of metals when AMG is applied, were only localized in digestive cell lysosomes. Digestive cell cytoplasm and basophilic cells were devoid of BSD. EPXMA (static probe and X-ray mapping) indicated that Cd, S (possibly associated with metallothioneins or metallothionein-like proteins) and autometallographical Ag ions are co-localized within digestive cell lysosomes. In addition, Cd and S co-occur in the absence of Ag in the cytosol of digestive cells. AMG does not reveal the presence of the Cd 'pool' strongly bound to cytosolic Cd-metallothionein complexes; only 'free' Cd or Cd supposedly loosely bound to (semi)digested metallothionein within lysosomes was revealed. The levels of lysosomal Cd were indirectly quantified by stereology as the volume density of BSD (V(v)BSD). Significantly higher values were recorded in Cd-exposed mussels compared with controls at all exposure times. However, V(v)BSD values were lower at days 7 and 21 than at day 1. This relative decrease in V(v)BSD reflected another (and confounding) response elicited by Cd-exposure in the digestive epithelium: the volume density of basophilic cells (V(v)BAS) increased significantly as exposure progressed. Due to this cell-type replacement, the net accumulative capacity of the digestive epithelium decreases at long exposure times.

Evidence of differences in the biotransformation of organic contaminants in three species of freshwater invertebrates

Acute static bioassays were performed using three freshwater invertebrate species (the oligochaete Lumbriculus variegatus, the fingernail clam Sphaerium corneum and the larvae Chironomus riparius) exposed separately to a variety of 14C radiolabelled contaminants. The aim of this work was to investigate if the chemicals remained as parent compounds after the treatments. Chemicals used were 2,4-dichlorophenol; 2,4,5-trichlorophenol; pentachlorophenol; pyrene; Fenpropidin, and Trifluralin. Homogenates of the whole body tissue of each organism were prepared and total radioactivity was measured. Contaminants were then extracted into organic solvents and analysed by high-pressure liquid chromatography techniques. Chromatograms showed that most of the substances extracted were present as parent compounds in S. corneum and in L. variegatus. In contrast, for C. riparius a low proportion of the chemicals was recovered as parent compounds. These results suggest that different metabolic processes could take place in the different species.

Vaccination of mice with a cocktail DNA vaccine induces a Th1-type immune response and partial protection against Schistosoma japonicum infection

Several defined vaccine candidate antigens of Schistosoma japonicum have shown promise in large animal vaccination experiments. However, vaccination of mice in the laboratory with either single recombinant antigens or DNA encoding forms of the individual antigens has so far failed to induce significant protection against S. japonicum cercarial challenge infection as judged by worm reduction, although specific antibodies were generated. This is in contrast to the results achieved using radiation-attenuated vaccines which are highly protective. Even in large animal vaccination experiments, the protection levels obtained with single defined antigens were far below those achieved using the attenuated vaccines. One possible interpretation is that the immune responses induced by single antigen vaccination may not be strong enough to combat the challenging infection. We, therefore, carried out mouse vaccination experiments using a cocktail DNA vaccine comprising four DNA plasmids encoding four different S. japonicum antigens, Sj62, Sj28, Sj23 and Sj14-3-3, respectively. We, also investigated whether co-injection of the mouse IL-12 encoding plasmid with the cocktail DNA vaccine was able to enhance the Th1 responses and hence the protective immunity. Three intramuscular injections of the cocktail DNA vaccine induced a significant Th1-type cellular response with high level of IFN-gamma production by splenocytes upon in vitro stimulation with recombinant antigens. Importantly, significant IgG antibody responses were also induced against crude worm antigens. In two out of three experiments, significant resistance (34-37 and 44-45%, respectively) was demonstrated while another experiment did not show any protection against S. japonicum cercarial challenge infection. Co-injection of the IL-12 encoding DNA did not further enhance these responses, nor the level of resistance, compared with the cocktail DNA alone.

Modeling pentachlorophenol bioavailability and bioaccumulation by the freshwater fingernail clam Sphaerium corneum using artificial particles and humic acids

The uptake of anthropogenic chemicals by benthic bivalves may occur through the water phase and also by the ingestion of particles from both the suspended matter and bottom sediments. Many chemicals sorb to sediments and, subsequently, are released in the digestive tract of animals. The assessment of sediment-bound chemicals has been difficult because of the complexity of the association between these chemicals and natural particles. To simplify this complexity, we previously devised a test system using artificial particles with known chemical structures. In the present work, we improved this experimental design by adding humic materials as a source of organic matter. Bioassays were conducted by exposing the fingernail clam Sphaerium corneum to sublethal levels of pentachlorophenol (PCP) in the presence or absence of the artificial particles, treated with or without a commercial preparation of humic acids. The results showed that the bioavailability and bioaccumulation could be explained on the basis of the interactions of PCP with the active groups and/or the backbone of the resins, both in systems with or without humic acids. This model may constitute a useful approach to modeling and predicting the uptake and accumulation of chemicals bound to natural sediments.

Laboratory and field evaluation of Schistosoma japonicum DNA vaccines in sheep and water buffalo in China

Vaccines are needed to control zoonotic Schistosoma japonicum infection and several vaccine candidates have now been identified. Two of these (Sj28GST and Sj23) have shown particular promise in sheep when injected with Freund's adjuvants. The objective of the present work was to find a vaccine formulation which may have potential for widespread use in the field. DNA vaccine formulations of these antigens were produced and tested first in sheep under laboratory conditions and then in both the laboratory and the field in water buffalo. In both host species partial protection as evidenced by a reduction in parasite counts in vaccinated compared with control animals was induced by both vaccines, and in water buffalo the vaccines were shown to be partially protective in the field as well as in the laboratory. These results suggest that the two DNA vaccines tested here may have potential for large-scale field use.

Higher northern latitude normalized difference vegetation index and growing season trends from 1982 to 1999

Normalized difference vegetation index data from the polar-orbiting National Oceanic and Atmospheric Administration meteorological satellites from 1982 to 1999 show significant variations in photosynthetic activity and growing season length at latitudes above 35 degrees N. Two distinct periods of increasing plant growth are apparent: 1982-1991 and 1992-1999, separated by a reduction from 1991 to 1992 associated with global cooling resulting from the volcanic eruption of Mt. Pinatubo in June 1991. The average May to September normalized difference vegetation index from 45 degrees N to 75 degrees N increased by 9% from 1982 to 1991, decreased by 5% from 1991 to 1992, and increased by 8% from 1992 to 1999. Variations in the normalized difference vegetation index were associated with variations in the start of the growing season of -5.6, +3.9, and -1.7 days respectively, for the three time periods. Our results support surface temperature increases within the same period at higher northern latitudes where temperature limits plant growth.

Members of the tomato LeEIL (EIN3-like) gene family are functionally redundant and regulate ethylene responses throughout plant development

The plant hormone ethylene regulates many aspects of growth, development and responses to the environment. The Arabidopsis ETHYLENE INSENSITIVE3 (EIN3) protein is a nuclear-localized component of the ethylene signal-transduction pathway with DNA-binding activity. Loss-of-function mutations in this protein result in ethylene insensitivity in Arabidopsis. To gain a better understanding of the ethylene signal-transduction pathway in tomato, we have identified three homologs of the Arabidopsis EIN3 gene (LeEILs). Each of these genes complemented the ein3-1 mutation in transgenic Arabidopsis, indicating that all are involved in ethylene signal transduction. Transgenic tomato plants with reduced expression of a single LeEIL gene did not exhibit significant changes in ethylene response; reduced expression of multiple tomato LeEIL genes was necessary to reduce ethylene sensitivity significantly. Reduced LeEIL expression affected all ethylene responses examined, including leaf epinasty, flower abscission, flower senescence and fruit ripening. Our results indicate that the LeEILs are functionally redundant and positive regulators of multiple ethylene responses throughout plant development.

Trace element speciation at cell membranes: aqueous, solid and lipid phase effects

Biological interest in trace element speciation has tended to be polarised in very different ways according to the concerns of the investigators. Much of the ecological interest has centred on the effects of metal ions in the external environment with the "free metal ion model" dominating discussions of potential toxicity. By way of contrast biochemists have been much more concerned with the stereochemical and kinetic aspects of specificity in metal protein interactions in the cytoplasm. Separating these two sets of interests are the membrane biophysicists whose studies have concentrated on the channel concept. All three groups have tended to ignore speciation onto the solid phase. In the overall biological context, trace element speciation in the cell is more concerned with kinetics and the evolution of specificity of interaction between diverse ligands than with the conditions for equilibrium.

The use of sediment analogues to study the uptake of pollutants by chironomid larvae

A technique is described that uses artificial resin beads with known surface properties to investigate the factors influencing the bioaccumulation of pollutants from sediments. One advantage of this technique is that it provides a standard procedure against which it is possible to calibrate natural sediments with their diverse properties. The method has been used on third instar larvae of the midge Chironomus riparius and the results are compared with previous studies on the worm Lumbriculus variegatus. The use of a standard test using resin beads as a substitute for natural sediment allows comparisons to be made between species and substrates. Thus, the bioaccumulation factors for the midge larvae are much smaller than those of the worm and this correlates with the ability of the insect larva to detoxify many pollutants. It is also possible to use the test to identify if ingestion of the sediment increases the bioaccumulation of contaminants and whether this involves the release of pollutants by digestive processes or not.

Can adsorption isotherms predict sediment bioavailability?

The adsorption and desorption of 2,4-dichlorophenol (DCP) and pentachlorophenol (PCP) were studied for a range of synthetic particles, a dimethylditallowammonium exchanged clay and a natural sediment. The synthetic particles were Dowex 1X8400, Toyopearl Phenyl 650M and Toyopearl SP 650M. The bioaccumulation of the DCP and PCP from these particles was then studied using the oligochaete, Lumbriculus variegatus. There is a correlation between contaminant-particle interactions, as determined from adsorption and desorption isotherms, and bioaccumulation. Bioaccumulation by L. variegatus was found to be highest from the systems where differences in the classification of adsorption and desorption isotherms were observed.

Cloning of Schistosoma japonicum 14-3-3 epsilon (Sj14-3-3 epsilon), a new member of the 14-3-3 family of proteins from schistosomes

A new member of the 14-3-3 protein family from Schistosoma japonicum has been identified. Phylogenetic analysis showed that this member belongs to the epsilon subfamily of the 14-3-3 proteins, and it is therefore named Sj14-3-3 epsilon. Consistent with the findings for the previously reported S. japonicum 14-3-3 protein (Sj14-3-3), Southern analysis suggested the presence of more than one gene, and/or introns or allelic polymorphism in this epsilon isoform. By RT-PCR, Sj14-3-3 epsilon was shown to be stage-specifically transcribed, being abundant in adults, present in sporocysts but absent in cercariae. Furthermore, mRNA of the epsilon isoform seemed to be much less abundant in the sporocyst stage, compared with Sj14-3-3. This suggests varying requirements of the different 14-3-3 isoforms at different stages of the life cycle.

The tomato ethylene receptors NR and LeETR4 are negative regulators of ethylene response and exhibit functional compensation within a multigene family

The plant hormone ethylene is involved in many developmental processes, including fruit ripening, abscission, senescence, and leaf epinasty. Tomato contains a family of ethylene receptors, designated LeETR1, LeETR2, NR, LeETR4, and LeETR5, with homology to the Arabidopsis ETR1 ethylene receptor. Transgenic plants with reduced LeETR4 gene expression display multiple symptoms of extreme ethylene sensitivity, including severe epinasty, enhanced flower senescence, and accelerated fruit ripening. Therefore, LeETR4 is a negative regulator of ethylene responses. Reduced expression of this single gene affects multiple developmental processes in tomato, whereas in Arabidopsis multiple ethylene receptors must be inactivated to increase ethylene response. Transgenic lines with reduced NR mRNA levels exhibit normal ethylene sensitivity but elevated levels of LeETR4 mRNA, indicating a functional compensation of LeETR4 for reduced NR expression. Overexpression of NR in lines with lowered LeETR4 gene expression eliminates the ethylene-sensitive phenotype, indicating that despite marked differences in structure these ethylene receptors are functionally redundant.

Immunogenicity of plasmid DNA encoding the 62 kDa fragment of Schistosoma japonicum myosin

The recombinant Schistosoma mansoni 62 kDa myosin fragment, rIrV-5, is highly protective in experimental animals, however, vaccination of mice and rats with the recombinant Schistosoma japonicum homologue, rSj62, did not induce significant resistance against S. japonicum infection. To explore alternative ways of presenting this antigen, we further constructed a plasmid (VRSj62) which encodes Sj62 using the VR1020 vector and tested it in vaccination experiments. Four immunisations with 10 microg VRSj62 DNA alone were sufficient to induce high and progressively increasing levels of IgG antibodies against rSj62 with increasing numbers of injections in CBA/Ca mice (IgG titre > or =1:25000), and three injections with 50 microg VRSj62 DNA alone induced significant IgG responses in C57Bl/6 mice (IgG titre, 1:1600). However, vaccination with plasmid DNA entrapped in cationic liposomes or together with pUC19 DNA as a source of CpG motifs, both of which have been reported to enhance immune responses, did not enhance specific antibody production. In spite of the stimulation of specific antibodies against rSj62 with the naked DNA construct no resistance to challenge was demonstrated.

Orthodontists' perceptions of the impact of phase 1 treatment for Class II malocclusion on phase 2 needs

The most appropriate timing for the treatment of Class II malocclusions is controversial. Some clinicians advocate starting a first phase in the mixed dentition, followed by a phase 2 in the permanent dentition. Others see no clear advantage to that approach and recommend that the entire treatment be done in the late mixed or early permanent dentition. This study examines how orthodontists, blinded to treatment approach, perceive the impact of phase 1 treatment on phase 2 needs. The sample consisted of 242 Class II subjects, aged 10 to 15, who had completed phase 1 or observation in a randomized clinical trial (RCT). For each subject, video orthodontic records, a questionnaire, a fact sheet, and a cephalometric tracing were sent to five randomly selected reviewing orthodontists blinded to subject group and study purpose. Reviewing orthodontists were asked to assess treatment need, general approach, need for extractions, priority, difficulty, and determinants. Orthodontists agreed highly on treatment need (95%) and moderately on treatment approach (84%) and extraction need (80%). They did not perceive differences in need, approach, or extractions between treated and control groups. Treated subjects were judged as less difficult (p = 0.0001) and to have a lower treatment priority (p = 0.0001) than controls. In ranking problems that affect treatment decisions, the orthodontists ranked dental Class II (p = 0.005) and skeletal relationships (p = 0.004) more highly in control than in treated patients. These data indicate that orthodontists do not perceive phase 1 treatment for Class II as preventing the need for a second phase or as offering any particular advantage with respect to preventing the need for extractions or other skeletal treatments in that second phase. They do view early Class II treatment as an effective means of reducing the difficulty of and priority for phase 2.

Molecular cloning and characterization of a novel Schistosoma japonicum "irradiated vaccine-specific" antigen, Sj14-3-3

A Schistosoma japonicum cDNA coding for a full length S. japonicum 14-3-3 protein was obtained by antibody screening of an adult worm cDNA library using sera taken from mice vaccinated with UV-attenuated cercariae, which are capable of transferring high levels of passive immunity to this parasite. The deduced amino acid sequence consists of 254 amino acids and is highly homologous with 14-3-3 family of proteins from a variety of species (55-69% identity). The recombinant S. japonicun 14-3-3 protein (rSj14-3-3) was expressed and purified in pGEX/E. coli, and in Western blotting was strongly recognised by sera from mice, rats and bovines vaccinated with irradiated S. japonicum cercariae. Analysis of mRNA showed that Sj14-3-3 is expressed in sporocysts and adult worms, but not in cercariae, however mouse antisera against rSj14-3-3 recognised a 29 kDa native antigen in antigen preparations made from eggs, cercariae, schistosomula and adult worms of S. japonicum indicating that this antigen is present in all life-cycle stages. The presence of the native antigen in detergent extracts of intact schistosomula suggests that it is also present in the schistosomular tegument which is the most vulnerable target for immune attack. However, antisera against rSj14-3-3 did not recognise a similar band in S. mansoni or S. haematobium antigens, indicating that, like the UV-attenuated vaccines, this protein induced species-specific immune responses. Southern blot analysis suggested that there may exist more than one gene copy and/or polymorphism for Sj14-3-3. Immunoelectron microscopy confirmed that the native antigen is present throughout the body of adult worms including the tegument, but is less abundant in the muscles. The potential of rSj14-3-3 as a vaccine is now under further investigation.

Evaluation of orthodontists' perception of treatment need and the peer assessment rating (PAR) index

This paper examines the relationship between orthodontists' subjective assessment of treatment need and objective measurements obtained during standardized intra- and extraoral examinations. Logistic regression modeling was used to develop predictive models of treatment need. Data were obtained from 1155 eighth-grade students by four orthodontists who used standardized examination forms to assess demographics, trauma, skeletal relationships, morphologic malocclusion traits, and mandibular function. At the conclusion of the examination, the orthodontist rated the subjective treatment need as none, elective, recommended, soon, or immediate. For some analyses, the categories were collapsed to represent no need and need. The peer assessment rating (PAR) index (American validated version) was computed from the clinical exam findings and scoring of dental models; PAR scores were used to document malocclusion severity and treatment difficulty. Spearman rank correlation coefficients quantified the relationship between PAR scores and need categories. Logistic regression analysis modeled treatment need using components of the PAR index as well as other variables. The components of these models, as well as sensitivity and specificity, were compared with malocclusion severity/treatment difficulty scores obtained from malocclusion assessments using the PAR index. The five subjective treatment need categories and the PAR index scores were significantly correlated (rho = 0.62, p<0.001). Significant differences were detected between the need and no need groups for all PAR components (p<0.001). PAR index scores and predicted probabilities from logistic regression models performed equally well for classification purposes (no need, need). The data suggest that the PAR index is highly correlated with orthodontists' subjective assessment of treatment need when that assessment is made in the absence of financial considerations and patient desires.

Vaccination of mice with gamma-irradiated Schistosoma japonicum cercariae

gamma-irradiated cercarial vaccines induce high levels of protection in mice against Schistosoma mansoni infection, however, the same has not been well established for S. japonicum. Here we describe vaccination studies in mice with gamma-irradiated S. japonicum cercariae testing the effectiveness of different irradiation doses, number of vaccinations, and mouse strains. In CBA/Ca mice, a single percutaneous exposure to 500 S. japonicum cercariae previously attenuated by 10, 20, 30, 40 or 50 krad gamma-irradiation induced significant, but comparable levels of protection (34-46%) against challenge infection. In a repeat experiment in C57Bl/6 mice, only groups vaccinated with 10 or 20 krad gamma-irradiated cercariae showed statistically significant, but lower levels of resistance (20-24%). Multiple vaccination of CBA/Ca mice with 500 20 krad gamma-irradiated cercariae did not improve the resistance level (40%). Analysis of IgG responses showed no clear correlation between antibody levels and levels of protection. Western blot analysis suggested that recognition of a 200-kDa antigen might be correlated with protection, that antigens of 42 and 50 kDa may be involved in the protection induced by single vaccination, but that different antigens might be protective in single vs multiple vaccinations. Sera from mice vaccinated with gamma-irradiated cercariae recognized many fewer antigens than more protective sera from mice vaccinated with UV-attenuated cercariae. These results suggest that the mouse may not be a suitable host for studies involving gamma-irradiated S. japonicum vaccines.

Schistosoma japonicum myosin: cloning, expression and vaccination studies with the homologue of the S. mansoni myosin fragment IrV-5

The Schistosoma japonicum homologue of the 62 kDa fragment of S. mansoni myosin (SmIrV-5), which has proved highly protective against S. mansoni infection in mice and rats, has been cloned and expressed as the full length 62 kDa equivalent, Sj62, and a truncated 44 kDa version, Sj44. DNA sequencing showed the Sj62 sequence to be 88.4% identical at the nucleic acid level and 96% identical in deduced amino acid sequence to that of SmIrV-5. The recombinant proteins (rSj44 and rSj62) were strongly recognized in Western blotting by sera from mice multiply vaccinated with UV-irradiated S. japonicum cercariae and weakly recognized by S. japonicum chronic infection mouse sera. Unlike SmIrV-5, mouse antisera against the recombinant S. japonicum proteins did not give positive recognition in immunofluorescence assay with the surface of newly transformed schistosomula of the homologous species, S. japonicum, nor did they react with S. mansoni schistosomula. However, the anti-rSj62 sera clearly localized the native antigen to the subtegumental muscle layers in male adult worm sections by immunoelectron microscopy. Vaccination of several groups of mice and/or rats with rSj44 and rSj62 incorporated into different adjuvants induced high titres of specific IgG but in only one experimental group was there a significant reduction in worm burden (27%, P < 0.05). The possible reasons for the disparity between the vaccination results presented here and those demonstrated in experiments using rSm62 (IrV-5) are discussed.

Quantitative evaluation of the chicken lysozyme epitope in the HyHEL-10 Fab complex: free energies and kinetics

The hen (chicken) egg-white lysozyme (HEWL) epitope for the monoclonal antibody HyHEL-10 Fab (Fab-10) was investigated by alanine scan mutagenesis. The association rate constants (k(on)) for the HEWL Fab-10 complexes were obtained from the homogenous solution method described in the preceding paper (Taylor et al., 1998). A new method for determining the dissociation rate constant (k(off)) for the complex, by trapping nascent free antibody with an inactive HEWL mutant is described. The values of k(on) fall within a factor of 2 of the wild-type (WT) HEWL value (1.43+/-0.13 X 10(6)M(-1)s(-1)), while the increases in k(off)more nearly reflect the total change in free energies of the complex (deltadeltaG(D)). The dissociation constants (K(D)) were measured directly in those cases where satisfactory kinetic data could not be obtained. The Y20A, K96A, and K97A HEWL.Fab-10 complexes are destabilized by more than 4 kcal/mol compared to the WT complex. The R21A, L75A, and D101A antibody complexes are moderately destabilized (0.7 < deltadeltaG(D)< or = 1.0 kcal/mol). Additional mutations of the "hotspot" residues (Tyr20, Lys96, Lys97) were constructed to probe, more precisely, the nature of their contributions to complex formation. The results show that the entire hydrocarbon side chains of Tyr20 and Lys97, and only the epsilon-amino group of Lys96, contribute to the stability of the complex. The value of deltadeltaG(D) for the R21A mutant complex is a distinct outlier in the Arg21 replacement series demonstrating the importance of supplementing alanine scan mutagenesis with additional mutations.

Kinetic epitope mapping of the chicken lysozyme.HyHEL-10 Fab complex: delineation of docking trajectories

The rate constants, k(on), for the formation of hen (chicken) lysozyme (HEWL). Fab-10 complexes have been determined for wild-type (WT) and epitope-mutated lysozymes by a homogeneous solution method based on the 95% reduced enzymatic activity of the complex. The values fall within a narrow 10-fold range [(0.18 to 1.92) x 10(6) M(-1)s(-l)]. The affinity constants, K(D), cover a broader, 440-fold, range from 0.075 to 33 nM. Values of K(D) as high as 7 microM were obtained for the complexes prepared from some mutations at HEWL positions 96 and 97, but the associated kinetic constants could not be determined. The values of k(on) are negatively correlated with side-chain volume at position 101HEWL, but are essentially independent of this parameter for position 21HEWL substitutions. The multiple mutations made at positions 21HEWL and 101HEWL provide sufficient experimental data on complex formation to evaluate phi values [phi = (deltadeltaGon)/(deltadeltaG(D))] at these two positions to begin to define trajectories for protein-protein association. The data, when interpreted within the concept of a two-step association sequence embracing a metastable encounter complex intermediate, argue that the rate determining step at position 21HEWL (phiavg = 0.2) is encounter complex formation, but the larger phi(avg) value of 0.36 experienced for most position 101HEWL mutations indicates a larger contribution from the post-encounter annealing process at this site for these replacements.