Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “PAPAIN”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 73 records · Page 4Linked to original sources
PubMed2004

Effect of water-soluble phospholipid polymers conjugated with papain on the enzymatic stability.

To maintain enzymatic activity during long-term storage by conjugation with water-soluble 2-methacryloyloxyethyl phosphorylcholine (MPC) polymers (PMPC-COOH) having various molecular weights with a carboxylic group on the terminal, such compounds were synthesized as a polymer modifier using a photoinduced living radical polymerization technique. A poly(ethylene oxide) with a carboxyl group (PEO-COOH) was used as the control. The PMPC-COOHs were reacted with the amino groups of the enzyme, papain, via amide bonds. With an increase in the molecular weight in the range between 5 and 20K of the PMPC-COOH, the modification degree and alpha-helix content of the conjugated papain slightly decreased, but the remaining enzymatic activity did not depend on the molecular weight of the PMPC-COOH. However, when a much higher molecular weight PMPC-COOH (40K) was conjugated with a reduction in the modification degree, alpha-helix content was higher compared with the other PMPC-conjugated papain. Modification with PEO-COOH showed little reduction of the alpha-helix content of papain. The time dependence of the remaining enzymatic activity of the polymer-conjugated papains was evaluated during storage at 40 degrees C. The native papain diminished activity within one week. PEO-conjugated papain had decreased activity with time, but after one week it had half its initial level. The same tendency was observed when papain was modified with PMPC-COOHs 5 and 40K, that is, the enzymatic activity did not decrease even when they were stored for 4 weeks. We concluded that the PMPC chain could stabilize the enzyme by control of the molecular weight of the PMPC and modification degree to the enzyme.

Biocompatible Materials↗
PubMed1993

Alterations of proteoglycan synthesis in rabbit articular cartilage induced by intra-articular injection of papain.

In order to investigate the biochemical alteration of proteoglycan (PG) synthesis during cartilage repair, reversible destruction was induced by injecting papain into the knee joint cavity of rabbits. The PG synthesis in the cartilage was examined using Na2 35SO4 and high performance liquid chromatography (HPLC). PGs labeled with 35SO4(2-) (35S-PGs) were extracted from normal and papain-treated cartilage, and the amount of synthesis, ability to aggregate with hyaluronan (HA), and the composition of glycosaminoglycan and chondroitin sulfate isomer labeled with 35SO4(2-) (35S-GAG and 35S-CS isomer) were analyzed. Synthesis of 35S-PGs, especially those that were unable to aggregate with HA (nonaggregating 35S-PGs), increased in papain-treated cartilage compared with that in normal cartilage. The acceleration and qualitative change in PG synthesis in the papain-treated cartilage are considered to be responses to the supplementation of the loss of cartilage PGs induced by papain. The compositions of 35S-GAG and 35S-CS isomer of the nonaggregating 35S-PGs differed from those of 35S-PGs which were able to aggregate with HA (aggregating 35S-PGs) in the papain-treated cartilage as well as in the normal cartilage. However, the compositions of both nonaggregating and aggregating 35S-PGs in the papain-treated and normal cartilage were similar. These results indicate that most of the nonaggregating 35S-PGs in papain-treated cartilage have properties similar to those in normal cartilage and are not simple degradation products of aggregating 35S-PGs; they also suggest that the supplementary reaction for PG content in the cartilage during its repair process is not simple acceleration in PG turn-over but the enhancement of PG synthesis accompanied by alterations in aggregating ability and the compositions of GAG and CS isomer.

Animals↗
PubMed2002

High-performance affinity chromatography for characterization of human immunoglobulin G digestion with papain.

Reactive continuous rods of macroporous poly(glycidyl methacrylate-co-ethylene dimethacrylate) were prepared within the confines of a stainless steel column. Then papain was immobilized on these monoliths either directly or linked by a spacer arm. In a further step, a protein A affinity column was used for the characterization of the digestion products of human immunoglobulin G (IgG) by papain. The results showed that papain immobilized on the monolithic rod through a spacer arm exhibits higher activity for the digestion of human IgG than that without a spacer arm. The apparent Michaelis-Menten kinetic constants of free and immobilized papain, K(m) and V(max), were determined. The digestion conditions of human IgG with free and immobilized papain were optimized. Comparison of the thermal stability of free and immobilized papain showed that the immobilized papain exhibited higher thermal stability than the free enzyme. The half-time of immobilized papain reaches about a week under optimum pH and temperature conditions.

Chromatography, Affinity↗
PubMed1991

Importance of hydrogen-bonding interactions involving the side chain of Asp158 in the catalytic mechanism of papain.

In a previous study, it was shown that replacing Asp158 in papain by Asn had little effect on activity and that the negatively charged carboxylate of Asp158 does not significantly stabilize the active site thiolate-imidazolium ion pair of papain (Ménard et al., 1990). In this paper, we report the kinetic characterization of three more mutants at this position: Asp158Gly, Asp158Ala, and Asp158Glu. From the pH-activity profiles of these and other mutants of papain, it has been possible to develop a model that enables us to dissect out the contribution of the various mutations toward (i) intrinsic activity, (ii) ion pair stability, and (iii) the electrostatic potential at the active site. Results obtained with mutants that place either Gly or Ala at position 158 indicate that the hydrogen bonds involving the side chain of Asp158 in wild-type papain are indirectly important for enzyme activity. When CBZ-Phe-Arg-MCA is used as a substrate, the (kcat/KM)obs values at pH 6.5 are 3650 and 494 M-1 s-1 for Asp158Gly and Asp158Ala, respectively, as compared to 119,000 M-1 s-1 for papain. Results with the Asp158Glu mutant suggest that the side chain of Glu moves closer to the active site and cannot form hydrogen bonds similar to those involving Asp158 in papain. From the four mutations introduced at position 158 in papain, we can conclude that it is not the charge but the hydrogen-bonding interactions involving the side chain of Asp158 that contribute the most to the stabilization of the thiolate-imidazolium ion pair in papain. However, the charge and the hydrogen bonds of Asp158 both contribute to the intrinsic activity of the enzyme.

Aspartic Acid↗
PubMed1978

Characterization of the papain active centre by using two-protonic-state electrophiles as reactivity probes. Evidence for nucleophilic reactivity in the un-interrupted cysteine-25-histidine-159 interactive system.

1.2,2'-Dipyridyl disulphide (2-Py-S-S-2-Py) and n-propyl 2-pyridyl disulphide (propyl-S-S-2-Py) were used as two-protonic-state reactivity probes to investigate the active centre of papain (EC 3.4.22.2).2. The existence of a striking rate optimum at pH approx. 4 in the reaction of papain not only with the symmetrical probe but also with the unsymmetrical probe is shown to constitute compelling evidence that the thiolate ion component of the cysteine-25-histidine-159 interactive system of papain possesses appreciable nucleophilic character. It is not a necessary requirement that the probe reagent should engage the imidazolium ion of histidine-159 in hydrogen-bonding for the sulphur atom of the interactive system to display nucleophilic character. The single proton-binding site of propyl-S-S-2-Py cannot simultaneously interrupt the active-centre ion pair and provide for rate enhancement as the pH is lowered towards 4. The possible implication of this for the mechanism of papain-catalysed hydrolysis is discussed. 3. The suspected difference in the active centres of papain and ficin (EC 3.4.22.3), which could be a lack in ficin of a carboxy group conformationally equivalent to that of aspartic acid-158 of papain is confirmed. The reactivity of the papain thiol group towards both probe reagents is controlled by two ionizations with pKa close to 4 that are positively co-operative. 4. In the reaction of papain with 2-Py-S-S-2-Py. the reactivity appears to be controlled also by an addition ionization with pKa approx. 5. Possible origins of this additional ionization are discussed. K. The spectral and ionization characteristics of propyl-S-S-2-Py are reported. 6. The reagent reacts rapidly with thiol groups at the sulphur atom distal from the pyridyl ring to provide, at pH values below 9, stoicheiometric release of 2-thiopyridone. This property, together with the ability of the reagent markedly to increase its electrophilicity consequent on protonation, suggests alkyl-2-pyridyl disulphides in general as valuable two-protonic-state reactivity probes with exceptional specificity for thiol groups.

2,2'-Dipyridyl↗
PubMed2000

Treatment of passively transferred experimental autoimmune myasthenia gravis using papain.

Antibody-mediated acetylcholine receptor (AChR) loss at the neuromuscular junction, the main cause of the symptoms of myasthenia gravis, is induced by bivalent or multivalent antibodies. Passive transfer of experimental autoimmune myasthenia gravis (EAMG) can be induced very efficiently in rats by administration of intact MoAbs directed against the main immunogenic region (MIR) of the AChR, but not by their monovalent Fab fragments. We tested whether papain, which has been used therapeutically in autoimmune and other diseases, is capable of preventing EAMG by in vivo cleavage of the circulating anti-AChR antibodies into Fab fragments. EAMG was induced in 4-week-old female Lewis rats by i.p. injection of anti-MIR mAb35. A total of 0.75 mg of papain was given as one or three injections 3-7 h after MoAb injection. The mAb35 + papain-treated animals developed mild weakness during the first 30 h and subsequently recovered, while all animals that received only mAb35 developed severe myasthenic symptoms and died within 24-30 h. Animals treated only with papain showed no apparent side effects for up to 2 months. Serum anti-AChR levels in mAb35 + papain-treated rats decreased within a few hours, whereas in non-papain-treated rats they remained high for at least 30 h. Muscle AChR in mAb35 + papain-treated animals was partially protected from antibody-mediated degradation. These results show that treatment of rats with papain can prevent passively transferred EAMG without any apparent harm to the animals, and suggest a potential therapeutic use for proteolytic enzymes in myasthenia gravis.

Animals↗
PubMedDate not supplied

Standardization of papain reagents by measurement of active sites using a synthetic inhibitor, E-64.

L-trans-epoxysuccinyl-leucylamido (4-guanidino) butane (E-64) reacts rapidly and irreversibly in a one-to-one ratio with the active site of papain, causing complete inhibition of the enzyme. After the addition of various concentrations of E-64 to a papain preparation, the residual enzyme activity can be measured using an azoprotein technique. The molarity of E-64 required to cause complete inhibition of papain activity is equal to the molarity of papain-active sites. Preparations of papain from various sources were assayed for protease activity by hydrolysis of azoalbumin using several variants of the basic technique and also by hydrolysis of azocasein. For each variant of azoprotein assay procedure, the active sites of the papain were measured using E-64. All variations of the azoprotein technique yielded similar estimates of the active site molarity of the papain preparations, whereas the azoprotein assay results alone showed wide variation. Quantitation of the active-site molarity of various papain preparations using E-64 correlated with serologic efficacy.

Azo Compounds↗
PubMed1995

[In vitro studies of the effect of papain on isolated chondrocytes: clinical relevance for correction of structural abnormalities of the ear].

A permanent change of shape of the auricle can be achieved by local application of papain to the elastic cartilage. To assess possible clinical use of papain, we investigated its effect on isolated and cultured chondrocytes derived from human cartilage of the auricle. We determined cellular vitality using the trypan blue method. The release of the cytokines IL-1 alpha and IL-6 measured by ELISA and HLA-DR antigen expression evaluated by histological procedures was used as a parameter of the state of activation of chondrocytes. Cell proliferation was also determined by the number of Ki-67 positive cells. A papain concentration above 160 micrograms/ml led to decreasing vitality and number of proliferating cells. A papain concentration above 160 micrograms/ml solvent led to expression of HLA-class-II-antigen on the surface of the chondrocytes. The release of IL-6 was reduced depending on the concentration of papain. However, IL-1 alpha was detected in low concentration with and without application of papain. These investigations show for the first time that papain not only leads to direct destruction of the matrix as described in literature, but also influences the integrity of the matrix by the function and state of activation of chondrocytes. A concentration of papain above 160 micrograms/ml should not be exceeded in clinical application.

Cartilage↗
PubMed1980

Fluorescence energy transfer studies on the active site of papain.

Measurements have been performed of the excited-state lifetimes and fluorescence yields of papain tryptophan units when acyl derivatives of Phe-glycinal are bound at the active site of the enzyme. The enhancement of tryptophan fluorescence in complexes of papain with the acetyl or benzyloxycarbonyl derivatives is not stereospecific with respect to the configuration of the phenylalanyl residue, and the L and D isomers are equally effective as active-site-directed inhibitors of papain action. Evidence is offered in favor of the conclusion that this enhancement is primarily a consequence of the interaction of the phenylalanyl side chain of the inhibitor with Trp-69 of the enzyme. This residue can exchange fluorescence energy with the other four tryptophans of papain (Trp-7, Trp-26, Trp-177, Trp-181) upon excitation near their absorption maxima, but such "homotransfer" is absent if they are excited at the long-wave edge of their absorption spectra. Crystallographic data indicate that Trp-26 is most favorably positioned for efficient energy exchange with Trp-69, and the fluorescence data have been used to calculate a distance of 11 A between the two residues; this value is in satisfactory agreement with that found by crystallography. When derivatives of Phe-glycinal bearing an amino-terminal mansyl [6-(N-methylanilino)-2-naphthalene sulfonyl] group are bound at the active site of papain, the tryptophan fluorescence is quenched, as compared with that of the complex of papain with acetyl-Phe-glycinal, indicating energy transfer from papain tryptophan (most probably via Trp-26) to the fluorescent probe group. Although the L and D isomers of mansyl-Phe-glycinal are equally effective as inhibitors of papain action, the fluorescence quenching by the two isomers is different.

Binding Sites↗
PubMed1986

Conformational changes of papain induced on interaction with thiol proteinase inhibitors from newborn rat epidermis.

The conformational changes of the papain molecular on interaction with two thiol proteinase inhibitors (TPI(1) and TPI(2] from newborn rat epidermis were studied by measuring circular dichroism (CD), the difference absorption spectrum, and the fluorescence spectrum due to tryptophan residues in papain. The far-ultraviolet CD band of papain between 210 and 230 nm was distinctly reduced on interaction with both inhibitors. Also, the near-ultraviolet CD spectrum of TPI(1)-bound papain changed between 285 and 320 nm as well as that of the TPI(2)-bound enzyme. The difference absorption spectrum for TPI(1)-bound papain exhibited two distinct peaks at 276.5 and 282 nm, indicating perturbation of aromatic amino acid residues. The fluorescence intensity of papain was significantly decreased on interaction with both inhibitors, which showed pH-dependency on an ionizable group, with pK values of 8.5 and 7.9 for TPI(1) and TPI(2), respectively. The complex formation of papain with both inhibitors caused a reduction of the susceptibility of a tryptophan residue, probably tryptophan-177, to chemical modification with N-bromosuccinimide. These results suggest that the active site involving histidine-159 in the papain molecule was much influenced by the alteration of the microenvironment of tryptophan-177 as a part of the interaction site for these two thiol proteinase inhibitors.

Animals↗
PubMed1982

[Enzyme activities of native non-enzymatically glucosylated trypsin, chymotrypsin and papain].

The proteases trypsin, alpha-chymotrypsin and papain were incubated with glucose for a period of 10 days at 37 degrees C and activity was tested in comparison to the enzymes incubated with the puffer solution only without glucose addition. Papain additionally was incubated for 10 days at 37 degrees C with the carbohydrates galactose, sucrose, lactose, glucosamine, galactosamine and mannosamine. While trypsin and chymotrypsin showed no change in enzymatic activity after incubation with glucose, the activity of papain was reduced by 70% to 90% (mean 84%). Incubation with galactose also inhibited papain activity but to a lesser extent (25% to 60%, mean 43%). Incubation with the other carbohydrates failed to inhibit papain activity. The mechanism inferred is nonenzymatic glucosylation of papain possibly as ketoamine linkage at the lysine residues situated close to the active site of papain causing steric or allosteric hindrance of the papain activity. The serine hydrolases trypsin and chymotrypsin without lysine residues near their active sites revealed unchanged activity after incubation with glucose.

Carbohydrate Metabolism↗
PubMed1975

Effect of papain on the interaction between human monocytes, erythrocytes, and IgG.

The mechanism by which papain detaches IgG-sensitized erythrocytes from the monocyte surface has been explored in an in vitro assay for the monocyte IgG receptor using red cells quantitatively sensitized with IgG anti-Rh D immunoglobulin. Papain treatment of IgG-sensitized erythrocytes diminished the ability of these cells to bind to the monocyte surface; however, treatment of erythrocytes with papain prior to sensitization with IgG did not inhibit binding, and at papain concentrations is greater than or equal to 38 mug/ml binding was enhanced. IgG receptor activity was not diminished by prior treatment of monolayer cells with papain and was enhanced with high concentrations of papain. These studies suggest that papain detaches erythrocytes from the monocyte surface by virtue of its proteolytic effect on IgG and not by an effect of papain on the D antigen of red cells or the IgG receptor on monocytes.

Animals↗
PubMed2006

Characterization of partially folded intermediates of papain in presence of cationic, anionic, and nonionic detergents at low pH.

A systematic investigation of the effects of detergents [Sodium dodecyl sulphate (SDS), hexa decyltrimethyl ammonium bromide (CTAB) and Tween-20] on the structure of acid-unfolded papain (EC.3.4.22.2) was made using circular dichroism (CD), intrinsic tryptophan fluorescence, and 1-anilino 8-sulfonic acid (ANS) binding. At pH 2, papain exhibits a substantial amount of secondary structure and is relatively less denatured compared with 6 M GdnHCl (guanidine hydrochloride) but loses the persistent tertiary contacts of the native state. Addition of detergents caused an induction of alpha-helical structure as evident from the increase in the mean residue ellipticity value at 208 and 222 nm. Near-UV CD spectra also showed the regain of native-like spectral features in the presence of 8 mM SDS and 3.5 mM CTAB. Induction of structure in acid-unfolded papain was greater in the presence SDS followed by CTAB and Tween-20. Intrinsic tryptophan fluorescence studies indicate the change in the environment of tryptophan residues upon addition of detergents to acid-unfolded papain. Addition of 8 mM SDS resulted in the loss of ANS binding sites exhibited by a decrease in ANS fluorescence intensity, suggesting the burial of hydrophobic patches. Maximum ANS binding was obtained in the presence of 0.1 mM Tween-20 followed by CTAB, indicating a compact "molten-globule"-like conformation with enhanced exposure of hydrophobic surface area. Acid-unfolded papain in the presence of detergents showed the partial recovery of enzymatic activity. These results suggest that papain at low pH and in the presence of SDS exists in a partially folded state characterized by native-like secondary structure and tertiary folds. While in the presence of Tween, acid-unfolded papain exists as a compact intermediate with molten-globule-like characteristics, viz. enhanced hydrophobic surface area and retention of secondary structure. While in the presence of CTAB it exists as a compact intermediate with regain of native-like secondary and partial tertiary structure as well as high ANS binding with the partially recovered enzymatic activity, i.e., a molten globule state with tertiary folds.

Biopolymers↗
PubMed1977

Preparation and properties of immobilized papain and lipase.

Papain and lipase were immobilized on derivatized Sepharose 4-B. The activated agarose had a binding capacity of 1.2 micronmol amino groups/ml packed agarose or 17 mg proteins/g dry agarose. The immobilized enzyme preparations were tested for the effects of pH of assay, temperature of assay, and substrate concentrations. The effect of 6M urea on the activity of papain was also determined. Soluble forms of the enzymes were used for comparison. Immobilization of the enzymes resulted in slightly different pH and temperature optima for activities. For immobilized papain Km(app) was similar to the one observed with soluble papain. Immobilization of lipase, however, cause a decrease in Km values. The immobilized enzyme preparations were stable when stored at 4 degrees C and pH 7.5 for periods up to eight months. The soluble enzymes lost their activity within 96 hr under similar storage conditions. Immobilized papain did not lose any activity after treatment with 6M urea for 270 min, whereas soluble papain lost 81% of its activity after the urea treatment, indicating that the immobilization of papain imparted structural and conformational stability to this enzyme.

Enzymes, Immobilized↗
PubMed1994

Stability and proteolytic activity of papain in reverse micellar and aqueous media: a kinetic and spectroscopic study.

The stability and proteolytic activity of papain were studied in reverse micellar systems, and in aqueous media. In reverse micelles the maximum activity obtained was 80% of the enzyme activity in aqueous solution. Higher papain stability was found in reverse micellar systems compared with that in aqueous solution with half-lives of 24 and 10 days respectively. Electron spin resonance (ESR) spectroscopy studies of aqueous and reverse micellar systems were performed in an attempt to explain the observed enzyme stability and activity profiles. For this purpose a spin label--TEMPOacetamide--was covalently linked to the Cys-25 residue of the papain active center. ESR spectra of labeled papain indicated that catalytic activity of papain could be related to the conformational rigidity near the reaction center. The lower activities obtained in reverse micelles could be a result of the greater degree of mobility and polarity observed in these systems, which can be attributed to papain unfolding. The greater stability found for papain in reverse micelles could be the result of the limited extent of this denaturing process owing to the organized surfactant molecules around the enzyme.

Benzoylarginine Nitroanilide↗
PubMed2001

Complex effects of papain on function and inhibitor sensitivity of the red cell anion exchanger AE1 suggest the presence of different transport subsites.

Band 3 (AE1), the anion exchanger of the human erythrocyte membrane, mediates not only fluxes of small hydrophilic anions (e.g., chloride, oxalate), but also the flip-flop of long-chain amphiphilic anions (e.g., dodecylsulfate). Treatment of erythrocytes with papain, long known to inhibit the transport of the former type of anions, accelerates the transport of the latter type. In an attempt to elucidate the basis of these opposite responses to papain, several small amphiphilic arylalkyl sulfonates and -sulfates were tested for the response of their transport, via AE1, to papain. Although all these probes are most likely transported by a flux and not by flip-flop, their transport was inhibited by papain only in some cases, but accelerated in others. Different responses to papain therefore most likely do not reflect differences between transport by flux or by flip. The transports of different species of anions also differed considerably in the changes of their sensitivity, to noncovalent and some covalent inhibitors, brought about by papain treatment. While oxalate transport remained as sensitive as in native cells, transports of small amphiphilic anions lost their sensitivity to a major extent, regardless of the inhibition or acceleration of their transport by papain. The results are discussed in the light of present concepts of the structural organisation of AE1, and interpreted in terms of a model of different transport subsites for different species of anions in this transporter.

Anion Exchange Protein 1, Erythrocyte↗
PubMed1998

X-ray crystal structure of papain complexed with cathepsin B-specific covalent-type inhibitor: substrate specificity and inhibitory activity.

The Ile-Pro sequence of CA074, potent covalent-type inhibitor, is necessary to exhibit the specificity for cathepsin B, but not for papain. In order to elucidate how its sequence binds to papain and why such binding does not exhibit the specificity for papain at the atomic level, two CA074-related compounds, 1 (N-(L-3-carboxyloxirane-2-carbonyl)-L-isoleucyl-L-proline) and 2 (N-(L-3-carboxyloxirane-2-carbonyl)-L-isoleucyl-diethylamide), were designed and their structure--inhibitory activity relationship was investigated by the X-ray crystal analyses of the complexes with papain. The Ile-Pro moiety of 1 was located at the S2 and S3 subsites consisting of Val-133, Val-157, and Asp-158 and of Tyr-61, Gly-66, and Tyr-67 residues of papain, respectively, which is in contrast with the binding of CA074 to S'n (n = 1 approximately 2) subsites in the complex with cathepsin B. Although 2 in the complex with papain showed the similar binding pattern to 1, its inhibitory activity was about two-fold higher than of 1, suggesting the importance of tight S3-P3 hydrophobic interaction for the activity. The difference of the substrate specificity between papain and cathepsin B has also been discussed based on the X-ray results of the present and cathepsin B-inhibitor complexes.

Cathepsin B↗
PubMed1992

Crystal structure of papain-succinyl-Gln-Val-Val-Ala-Ala-p-nitroanilide complex at 1.7-A resolution: noncovalent binding mode of a common sequence of endogenous thiol protease inhibitors.

Succinyl-Gln-Val-Val-Ala-Ala-p-nitroanilide corresponding to a common sequence of endogenous thiol protease inhibitors is a noncompetitive reversible inhibitor of papain. In order to elucidate the binding mode of the inhibitor at the atomic level, its complex with papain was crystallized at ca. pH 7.0 using the hanging drop method, and the crystal structure was analyzed at 1.7-A resolution. The crystal has space group P2(1)2(1)2(1), with a = 43.09, b = 102.32, c = 49.69 A, and Z = 4. A total of 47,215 observed reflections were collected on the imaging plates using the same single crystal, and 19,833 unique reflections with Fo > sigma (Fo) were used for structure determination and refinement. The papain structure was determined by use of the atomic coordinates of papain previously reported, and then refined by the X-PLOR program. The inhibitor molecule was located on a difference Fourier map and fitted into the electron density with the aid of computer graphics. The complex structure was finally refined to R = 19.6% including 118 solvent molecules. The X-ray analysis of the complex crystal shows that the inhibitor is located at the R-domain side, not in the center of the binding site created by the R- and L-domains of papain. Such a binding mode of the inhibitor explains well the biological behavior that the inhibitor exhibits against papain. Comparison with the structure of papain-stefin B complex indicates that the structure of the Gln-Val-Val-Ala-Gly sequence itself is not necessarily the essential requisite for inhibitory activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗