Sequence comparison between the flavoprotein subunit of the fumarate reductase (complex II) of the anaerobic parasitic nematode, Ascaris suum and the succinate dehydrogenase of the aerobic, free-living nematode, Caenorhabditis elegans

Complex II in adult mitochondria of the parasitic nematode, Ascaris suum, exhibits high fumarate reductase activity and plays a key role in the anaerobic electron-transport observed in these organelles. In the present study, cDNAs for the flavoprotein (Fp) subunits of complex II have been isolated, cloned and sequenced from both A. suum and the aerobic, free-living nematode, Caenorhabditis elegans. Additional sequence at the 3' end of the mRNAs was determined by the Rapid Amplification of cDNA Ends (RACE). Nucleotide sequence analysis of the A. suum cDNAs revealed a 22-nucleotide trans-spliced leader sequence characteristic of many nematode mRNAs, an open reading frame of 1935 nucleotides and a 3' untranslated region of 616 nucleotides including a poly (A) tail from a polyadenylation signal (AATAAA). The open reading frame encoded a 645 amino acid sequence, including a 30 amino acid mitochondrial presequence. The amino acid sequences for the Fp subunits from both organisms were very similar, even though the ascarid enzyme functions physiologically as a fumarate reductase and the C. elegans enzyme a succinate dehydrogenase. The ascarid sequence was much less similar to the Escherichia coli fumarate reductase. The sensitivity of other Fp subunits to sulfhydryl reagents appears to reside in a cysteine immediately preceding a conserved arginine in the putative active site. In both nematode sequences, this cysteine is replaced by serine even though the succinate dehydrogenase activity of both enzymes is still sensitive to sulfhydryl inhibition. A cysteine six residues upstream of the serine may be involved in the sulfhydryl sensitivity of the nematode enzymes. Surprisingly, in contrast to succinate dehydrogenase activity, the fumarate reductase activity of the ascarid enzyme was not sensitive to sulfhydryl inhibition, suggesting that the mechanism of the two reactions involves separate catalytic processes.

[Postural sway in patients with hereditary ataxia]

Instability of erect stance in patients with autosomal dominant hereditary ataxia was investigated by posturography. Postural sway on a force-measuring platform was measured quantitatively and sway frequencies were analyzed. Thirty patients from 27 families (15 men and 15 women, mean age of 53.1 years (SD 11.1)) were divided into two clinical groups. Twelve patients (group A) had "pure" cerebellar signs with no somatosensory afferent symptoms. Eighteen patients (group B) had sensory disturbances or diminished reflexes of the lower limbs, and a delayed latency of scalp P37 in somatosensory evoked potentials subsequent to tibial nerve stimulation. Postural sway of the patients of both groups was larger than that of normal subjects. Group A patients had a high antero-posterior/lateral sway ratio. Group B patients had increased sway with eyes closed. With respect to sway frequencies, group A patients had a power spectrum peak around 3 Hz. Group B patients had a power spectrum peak around 1 Hz, and twelve of them had another 3 Hz component. Atrophy of the anterior lobe of the cerebellum shown by MRI was more prominent in patients who had the 3 Hz power spectrum peak than in patients lacking the 3 Hz peak. Quantitative posturography was useful to detect disturbances of the anterior lobe of the cerebellum and the spinal ascending system in patients with autosomal dominant hereditary ataxia.

Three novel subtilisin-trypsin inhibitors from Streptomyces: primary structures and inhibitory properties

Three novel proteinaceous inhibitors, which had been identified as "Streptomyces subtilisin inhibitor-like (SIL) proteins" and exhibited trypsin inhibition in addition to strong inhibition toward subtilisin BPN', were purified from the culture broth of three Streptomyces strains: SIL10 from S. thermotolerans, SIL13 from S. galbus, and SIL14 from S. azureus. Their primary structures were determined by sequence analysis of intact SIL inhibitors and peptides obtained by enzymatic digestions of S-pyridylethylated SIL inhibitors. These inhibitors were composed of about 110 amino acids and existed as dimer proteins. The reactive site was identified as Lys-Gln for all three inhibitors by sequence analysis of their modified forms in which the reactive-site peptide bond was specifically cleaved by subtilisin BPN' under acidic conditions. Thus, their inhibition toward trypsin and subtilisin BPN' was due to the presence of a Lys residue at the P1 site. Inhibitor constants toward subtilisin BPN' and trypsin were also determined. These inhibitors showed relatively high sequence homology to other SSI-family inhibitors possessing a Lys residue at the P1 site, with amino acid replacements on their molecular surface.

Effects of chelating agents on tissue distribution and excretion of nickel in mice

N-Benzyl-D-glucaminedithiocarbamate (BGD), diethyldithiocarbamate (DDTC), di-hydroxyethyldithiocarbamate (DHED), trans-1,2-cyclohexanediamine N,N,N',N'-tetra-acetic acid (CDTA), and 2,3-dimercaptosuccinic acid (DMSA) were studied for their relative efficacies in the distribution and excretion of nickel in mice exposed to nickel. Mice were injected intraperitoneally with NiCl2 (5mgNi/kg) and 30 min or 24 hr later, they were injected intraperitoneally with chelating agents (400 mumol/kg). At 30 min after treatment with nickel, these chelating agents all significantly enhanced the fecal excretion of nickel, and DMSA significantly increased the urinary excretion of the metal. At 24 hr after nickel treatment, BGD, DDTC, and DHED significantly increased the fecal excretion of nickel and BGD was the most effective on the fecal excretion of nickel. CDTA and DMSA significantly enhanced the urinary excretion of the metal. At 30 min after nickel treatment, chelating agents other than CDTA effectively depressed nickel concentration in the kidney, lung, and testes. BGD, CDTA, and DMSA significantly reduced the nickel concentration in the liver. However, DDTC and DHED caused the redistribution of nickel to the brain. At 24 hr after nickel treatment, these chelating agents were effective in mobilizing nickel from the kidney, and chelating agents other than DHED were effective in mobilizing nickel from the liver, lung, and testes. These results indicate that the injection of BGD or DMSA at both 30 min and 24 hr after treatment with nickel can remove nickel from the body without redistribution of nickel to other tissues, such as brain, more effectively than DDTC, DHED, and CDTA. Furthermore, the pattern of excretion of nickel after treatment with the chelating agents was related to the partition coefficients of the nickel-chelating agent complexes.

[Necessity of cerebral angiography in thunderclap headache patients who show no evidence of subarachnoid hemorrhage: investigation of 350 cases]

PURPOSE

The necessity of cerebral angiography was assessed in patients with thunderclap headache in whom subarachnoid hemorrhage had been ruled out on CT findings and the color of cerebrospinal fluid (CSF).

SUBJECTS AND METHODS

The subjects of this study were 350 patients with thunderclap headache in whom subarachnoid hemorrhage was ruled out at our clinic based on CT findings and the color of CSF. The time span from the onset of thunderclap headache to the first visit to our clinic ranged from 1 to 9 days (mean: 2.5 days). The ages of the patients ranged from 22 to 64 years. 147 were male and 203 female. All patients underwent CT angiography. Percutaneous cerebral angiography was also performed in cases in which cerebral aneurysms were suspected on CT angiography or the CSF cell count was elevated (over 10/3mm3 on white blood cells).

RESULTS

(1) Of the 350 patients, 162 were suspected to have cerebral aneurysms when examined by CT angiography. When these 162 patients were examined by percutaneous cerebral angiography, cerebral aneurysms were found in 34 patients (9.7%). (2) Four patients had an elevated CSF cell count. Cerebral aneurysms were found in all these patients. (3) Of the 34 patients with cerebral aneurysms, 31 consented to and underwent direct surgery. Localized subarachnoid hemorrhage around their aneurysms was found in seven (22.6%) of these 31 patients intraoperatively. Elevation in CSF cell count was shown in three of these patients.

CONCLUSION

Even when CT and CSF studies reveal no abnormalities in the early stage after the onset of thunderclap headache, subarachnoid hemorrhage can not be ruled out. Therefore, cerebral angiography is recommended in patients with thunderclap headache.

Intracellular calcium transients in potentiated contractions induced by multiple extrasystolic beats in isolated perfused rat hearts

Mechanisms underlying contractile potentiation induced by multiple extrasystolic contractions (ESC) were evaluated with surface fluorometry in isolated perfused rat hearts loaded with Indo-1/AM. After baseline pacing with a 400 ms interval, 1-25 ESC were interposed with a regular 160 ms interval followed by the postextrasystolic beat with a 400 ms interval. With an increase in the ESC number, left ventricular developed pressure and peak positive dP/dt increased in an exponential manner, reaching a plateau, that was the same for 3 extracellular Ca2+ ([Ca2+]o; 0.55 (n = 9), 1.25 (n = 11) and 2.75 mM (n = 7). Increased [Ca2+]o shifted this relationship left and upward, and with 2.75 mM [Ca2+]o developed pressure and dP/dt decreased after the maximum potentiation was obtained. The relationship between the ESC number and the amplitude of the Indo-1 fluorescence (F400/F510; an index of intracellular Ca2+ ([Ca2+]i)) was also exponential and was shifted left and upward by high [Ca2+]o; however, it lacked the declining phase. Thus, the relationship between the amplitude of F400/F510 and developed pressure or dP/dt consisted of a positively linear part until the maximum potentiation was obtained and a negatively linear part with a further increase in the amplitude of F400/F510. This observation suggests that although contractile potentiation is mediated by increased [Ca2+]i transients, the maximum response might be determined by the responsiveness of the sarcomere.

Antioxidative activity of benzylideneascorbate and its effect on adriamycin-induced cardiotoxicity

The in vitro antioxidative activity of benzylideneascorbate (SBA) and the in vivo effect on adriamycin (ADR)-induced cardiotoxicity in a mouse model were investigated. The radical-scavenging activity of SBA was assayed in terms of reduction of chemiluminescence induced by O2-, generated in xanthine/xanthine oxidase and macrophage/phorbol myristate acetate reaction systems. SBA showed a strong antioxidative activity (IC50 = 3 to 4 microM) in both assay systems, though its activity was weaker than that of ascorbic acid (Asc). In the assay of the antioxidative activity against auto-oxidation of linolenic acid, SBA was stable and retained its potency for a long period of time in comparison with Asc, 6-palmitoylascorbic acid (6-P-Asc) and cysteamine (CysNH2). Electron spin resonance examination indicated that SBA strongly scavenged both superoxide anion and hydroxy radical. The in vivo protective effect of SBA against ADR-induced cardiotoxicity, in which active oxygen radicals play a role, was examined. The serum creatine phosphokinase activity, a parameter of cardiotoxicity, was remarkably increased from the 3rd day until the 4th day after ADR treatment. This elevation was significantly suppressed by SBA treatment, whereas Asc, 6-P-Asc and CysNH2 were ineffective. SBA could have clinical potential for the treatment of diabetes and other disorders in which active oxygen species play a pathogenic role.

Renaturation of the mature subtilisin BPN' immobilized on agarose beads

We report here another example of renaturation of subtilisin BPN'(Sbtl) by using an immobilized preparation instead of applying a digestible mutant of Streptomyces subtilisin inhibitor (SSI), a proteinaceous inhibitor of Sbtl [M. Matsubara et al. (1994) FEBS Letters 342, 193-196]. The mature Sbtl was immobilized on agarose beads employing the amino group of the protein. After thorough washing, the immobilized Sbtl was subjected to denaturation in 6 M guanidine hydrochloride (GdnHCl) at pH 2.4 for 4 h, followed by renaturation in 2 M potassium acetate at pH 6.5 for 24 h. This denaturation/renaturation cycle was repeated five times. The recovered activity of the renatured immobilized Sbtl settled at a constant level after the third denaturation/renaturation cycle, demonstrating that almost 100% renaturation was attained by use of the immobilized Sbtl. This immobilized Sbtl preparation could well be utilized for the mechanistic study of protein folding. We then found that 2 M potassium acetate was superior to 2 M potassium chloride as a refolding medium and that the ability of SSI to induce the correct shape of the mature Sbtl was lacking in several refolding media in both thermodynamic and kinetic criteria. Thus the main cause for the increase of refolding yield of Sbtl by coexistence of SSI was prevention of the autolysis of Sbtl.

A new protocol and criteria for quantitative determination of sensitization potencies of chemicals by guinea pig maximization test

This paper presents precise sensitization test data of 15 chemicals with a wide spectrum of sensitization potencies, and proposes a new protocol and criteria for quantitative evaluation of sensitization potencies of chemicals. The tests were performed according to the design of Magnusson and Kligman, changing the application concentrations for induction as well as for challenge phases. 3-dimensional relationships between mean response (or sensitization rate), induction and challenge concentrations were found in all chemicals tested. The following 2 values are proposed as a quantitative measure of sensitization potency: (a) the minimum induction concentration that induces a positive response; (b) the challenge concentration that induces a mean response approximately equal to 1.0 among the animals applied with the highest concentration for induction. Both values coincided with each other within the range of 1 order of magnitude in every compound except 2. The values varied by 5 orders or more of magnitude among the compounds, showing a wide variation of sensitization potencies among chemicals. A good correlation was found for every chemical between the value of sensitization potency thus obtained and the residual levels in causative products in human cases of allergic contact dermatitis. A new experimental protocol for obtaining values (a) and (b) is proposed.

[Involuntary movements caused by thalamic lesion]

We described two types of involuntary movement accompanied with a well-located thalmaic lesion shown by MR imaging in five patients. All patients had the involuntary movements of an upper limb contralateral to the thalamic lesion. Two patients (1 and 2) had choreoathetosis that became most prominent when their index finger approached their nose, where irregular and dysynchronous oscillation occasionally superimposed. This choreoathetosis was differentiated from pseudoathetosis caused by disturbance of proprioceptive sensations. The MRI lesion was located at the middle level of thalamus including nucleus centromedianus. The other three patients (3, 4 and 5) had a regular and rhythmic oscillation in their forearm. The oscillation began to appear after their index finger reached their nose on finger-to-nose test. We considered the oscillation as a postural tremor based on its rhythmicity and regularity. Patient 4 had additional tremor in movement. Their postural tremor continued while the arm kept the position. Surface electromyogram showed the reciprocal discharges between the forearm extensor and flexor muscles with a frequency of 3 to 4 Hz. This tremor was not accentuated during limb movement toward the nose nor was coarse, and was distinguished from intention tremor described by Charcot and Dejerine. This tremor was also different from hyperkinesis volitionnelle and movement oppositionist. The "rubral tremor" differed from the tremor shown in our cases for a lack of resting tremor. The responsible lesion shown by MRI located at caudal posterior thalamus including pulvinar in patient 3, or located at the upper level of thalamus in patient 4 and case 5 that was more rostral than the lesion of the choreoathetosis cases. In cases of cerebrovascular accidents, both types of involuntary movement appeared after several months from the stroke. This delayed appearance suggests that these involuntary movements were the result not only of functional disturbance of thalamus, but of secondary repairing mechanism occurring at the lesion.

Effect of terbium on protease activity in pancreas of mice

The effect of terbium (Tb) on the protease activity in pancreas of mice was studied. Administration of Tb at doses of 20 and 200 mumol/kg increased the activities of trypsin and carboxypeptidase A, but did not affect the activities of chymotrypsin and carboxypeptidase B. High Tb concentrations were found in the liver and spleen compared to the kidney and pancreas. Increases in Ca concentrations in the pancreas, kidney, and spleen after Tb administration were observed. The pancreatic slice experiments showed the increase in trypsin activity after Tb treatment and increases in trypsin and carboxypeptidase A after Ca treatment. Tb inhibited strongly the activities of authentic chymotrypsin and carboxypeptidase A. These results suggest that the increase in trypsin activity in the pancreas after Tb administration results from the activation of trypsinogen by Tb and Ca ions and that the increase in carboxypeptidase A activity is due to the activation of procarboxypeptidase A by trypsin and Ca ion, which increased after Tb administration.

Primary structure and inhibitory properties of a proteinase inhibitor produced by Streptomyces cacaoi

Protein proteinase inhibitors showing sequence homology with Streptomyces subtilisin inhibitor (SSI) have been found to be distributed widely in Streptomyces species, and accordingly have been named SSI-like (SIL) proteins. SIL1 from S. cacaoi was the first of these proteins to be isolated and to be given a serial number. To study the structure-function relationship of SIL proteins, we determined the primary structure of SIL1 and measured its inhibitory activities. It was found to be composed of 110 amino acids and to exist in dimer form. The amino-acid sequence of SIL1 was unique among other characterized SIL proteins in having a one-residue deletion in two regions and a three-residue insertion in the flexible loop region. Sequence comparison indicated that SIL1 was distantly related to other members of the SSI family, and that amino-acid replacements had occurred not only on the surface of the SIL1 molecule but also in the beta-sheet region. The reactive site of SIL1 was considered to be Arg70-Glu71 from sequence alignment with other SSI-family inhibitors. SIL1 inhibited subtilisin BPN' strongly with an inhibitor constant (Ki) of 2.8 x 10(-11) M, like other members of the SSI family possessing an Arg residue at the P1 site. In contrast, SIL1 exhibited weak inhibition toward trypsin with a Ki value of 5.5 x 10(-8) M, possibly as a consequence of insertion of the three residues in the flexible loop region near the reactive site. This contrast seems to be due to the difference in the subsite structure of the two proteinases.

The absence of IgE antibody-mediated augmentation of immune responses in CD23-deficient mice

The CD23 antigen, a low-affinity receptor for IgE (Fc epsilon RII), is a type II membrane-bound glycoprotein expressed on various cells, particularly mature B cells. A number of functions have been ascribed to CD23, including specific regulation of IgE production, IgE-mediated cytotoxicity and release of mediators, IgE-dependent antigen focusing, promotion of B-cell growth, prevention of germinal center B cells from apoptosis, proliferation of myeloid precursors, and maturation of early thymocytes. It is not clear whether these activities represent in vivo functions. To explore in vivo functions of CD23, we have produced CD23-deficient mice. These mice displayed normal lymphocyte differentiation and could mount normal antibody responses, including IgE responses upon immunization with T-dependent antigens and infection with Nippostrongyrus brasiliensis. Germinal center formation after immunization and in vitro proliferative response of B cells were not affected in mutant mice. However, antigen-specific IgE-mediated enhancement of antibody responses was severely impaired.

Inhibition of carbon tetrachloride-induced hepatotoxicity by neopterins

We investigated the inhibitory effects of neopterin (NP) and its reduced form, 5,6,7,8-tetrahydroneopterin (NPH4), on carbon tetrachloride (CCl4)-induced hepatotoxicity. In in vivo experiments, intraperitoneal administration of NP or NPH4 significantly inhibited the elevation of plasma alanine aminotransferase activity induced by CCl4 in mice. In in vitro experiments using cultured rat hepatocytes, CCl4 induced in a manner which was both time- and dose-dependent lactate dehydrogenase release, and the addition of NP or NPH4 to the culture-medium significantly inhibited its release from cells. NPH4, but not NP, reacted directly with a stable radical, 1,1-diphenyl-2-picrylhydrazyl. These results suggest that NP and NPH4 inhibit CCl4-induced hepatotoxicity through different mechanisms.

Physical stability and protein stability of freeze-dried cakes during storage at elevated temperatures

The relationship between physical stability of freeze-dried cakes and protein stability during storage was studied using beta-galactosidase as a model protein and inositol as an excipient. Amorphous samples freeze-dried from solutions containing the enzyme and various concentrations of inositol in sodium phosphate buffer (50 mM, pH 7.4) were stored for 7 days over P2O5 at 40 to 70 degrees C. Structural collapse and inositol crystallization were observed in some of the samples, depending on the formulation and storage temperature. The physical stability of freeze-dried samples was also studied by differential scanning calorimeter (DSC). Inositol showed a protein-stabilizing effect when its amorphous form was retained during storage, regardless of structural collapse. However, crystallization of inositol during storage removed its stabilizing effect. Addition of water-soluble polymers such as dextran, Ficoll and carboxymethyl cellulose sodium salt (CMC-Na) preserved activity of the enzyme by preventing inositol crystallization.

Human complex II (succinate-ubiquinone oxidoreductase): cDNA cloning of the flavoprotein (Fp) subunit of liver mitochondria

Complex II (succinate-ubiquinone oxidoreductase) is an important enzyme complex in both the tricarboxylic acid cycle, and the aerobic respiratory chains of mitochondria in eukaryotic cells and prokaryotic organisms. In this study, homology probing with mixed primers for the polymerase chain reaction and subsequent sequence analysis were successfully applied to clone cDNA for the flavoprotein (Fp) subunit of human liver complex II. The isolated clone contains an open reading frame of 1,992 nucleotides and encodes a mature protein of 621 amino acids with a molecular weight of 68,011. The amino acid sequence was highly homologous with that of bovine heart Fp (93.2%) and was quite different from the partial sequence of human placental Fp reported previously [Malcovati et al. (1991) in Flavins and Flavoproteins 1990, pp. 727-730], which showed striking homology to that of Bacillus subtilis. To solve this discrepancy, the partial cDNA sequences of the stomach and placental Fp subunits of human complex II were determined in addition to the full length cDNA of liver. The sequence data, sensitivity to thiol reagents and antigenic properties indicated that the major from of FP subunit in human complex II is unique at least among the three tissues analyzed, and is more similar to the Fp subunit of bovine heart than to that of B. subtilis.

The association between salt sensitivity of blood pressure and some polymorphic factors

OBJECTIVE

To examine the association in Japanese subjects between the salt sensitivity of blood pressure and polymorphic factors.

DESIGN AND METHODS

One hundred and four patients with essential hypertension were classified as salt-sensitive or non-salt-sensitive depending on their blood pressure response to salt restriction. An insertion/deletion polymorphism of the angiotensin converting enzyme (ACE) gene was examined by detecting an alu sequence in intron 16. The ACE genotype was classified as II, ID or DD depending on whether each allele had this sequence. The haptoglobin phenotype was determined by the starch-gel electrophoresis method, and was classified as three phenotypes, 1-1, 2-1 or 2-2 form.

RESULTS

The response of plasma renin activity to salt restriction was greater in patients with the DD form than in those with other forms, although there were no significant differences in the ratio salt-sensitive: non-salt-sensitive patients among the three ACE genotype groups. However, the ratio was significantly larger in the haptoglobin 2-1 phenotype group than in the 2-2 group.

CONCLUSIONS

The salt sensitivity of blood pressure was associated with the haptoglobin phenotype, but was not associated with the ACE genotype. However, the response of plasma renin activity to salt restriction was different according to the ACE genotype.

[Outcome of treatment protocol 8704T for childhood T cell leukemia and lymphoma]

We reported the treatment outcome of Protocol 8704T, which included repeated L-asparaginase, for childhood T cell malignancies. Fifteen cases of acute lymphoblastic leukemia (T-ALL) and 11 cases of non-Hodgkin's lymphoma (T-NHL), aged 3 to 14 yrs (median 6 yrs), were enrolled. Twelve T-ALL had mediastinal mass. Murphy's stages of T-NHL were 6 with III and 5 with IV. Types of histology consisted of 8 lymphoblastic and 3 large cell. Treatment was performed for 2 years. Observation periods were from 14 months to 78 months (median 42 months). Twenty-three achieved remission and 6 of them were transplanted with bone marrow or peripheral stem cells in the first remission. The protocol was continued in 17 cases. Fourteen of them remain in first remission, but one died of measles and 2 died of relapse. The 5-year event-free survival was 76.1% for ALL and 65.5% for NHL. In terms of histology, it was 87.5% for lymphoblastic NHL and 33.3% for large cell NHL (p = 0.19). In terms of phenotypes in ALL, it was 88.7% for ALL positive to CD2, 5 and 7, while 2 ALL positive to CD7 alone both failed. Therefore, it was shown that this treatment protocol is very effective for T-lymphoblastic leukemia and lymphoma.

Secretory production of chicken ovomucoid domain 3 by Escherichia coli and alteration of inhibitory specificity toward proteases by substitution of the P1 site residue

Ovomucoids are commonly present in bird egg white and exhibit inhibitory activity toward various serine proteases. To investigate the structure-function relationship of ovomucoid domain 3, we established a secretory expression system for the chicken ovomucoid domain 3 (OMCHI3)-encoding gene in Escherichia coli by ligating it downstream from the tac promoter and signal peptide of E. coli alkaline phosphatase. E. coli JM105 was transformed with the resulting plasmid and induced with 1 mM isopropyl-beta-D-thiogalactopyranoside (IPTG). The mature OMCHI3 was detected in the culture supernatant, and was purified to homogeneity by three-step chromatography. Amino-acid sequence analysis showed that processing by the signal peptidase was carried out exactly at the expected site. Measurements of circular dichroism spectra and inhibitory activity indicated that OMCHI3 was produced in the properly folded form. Furthermore, site-specific replacement of the Ala residue at the P1 site with Met or Lys resulted in acquisition of inhibitory activity toward chymotrypsin or trypsin, respectively, indicating that the P1 site is the predominant determinant for inhibitory specificity.