Biomedical subjects

H K Song

Publications and source records attributed to H K Song.

At least 73 records · Page 4Linked to original sources

PubMed1998

Changing presentation and management of neutropenic enterocolitis.

OBJECTIVE: To characterize the current clinical presentation and management of neutropenic enterocolitis. DESIGN: Retrospective review of records of oncology unit patients requiring general surgical consultation for abdominal complaints in a 1-year period. SETTING: Oncology unit of a tertiary care, university teaching hospital. PATIENTS AND INTERVENTIONS: Fourteen patients diagnosed as having neutropenic enterocolitis were managed conservatively with operation reserved for failure of conservative therapy. MAIN OUTCOME MEASURES: Clinical data from patients at the time of presentation and during treatment for neutropenic enterocolitis. RESULTS: All 14 patients diagnosed as having neutropenic enterocolitis were receiving chemotherapy for solid tumors or leukemias. Seven patients were undergoing stem cell or autologous bone marrow transplantation. Presenting symptoms and physical examination findings were nonspecific. All patients except one had neutropenia at the time of diagnosis. Computed tomographic scans of the abdomen were the most useful confirmatory study for the diagnosis of neutropenic enterocolitis. All patients except one had resolution of neutropenic enterocolitis with conservative therapy. One patient whose course of conservative management failed had protracted neutropenia and required operation for resection of bowel with full-thickness necrosis. CONCLUSIONS: Neutropenic enterocolitis has evolved from a complication of patients with leukemia to a disease of patients receiving high-dose chemotherapy for many malignancies, solid as well as hematologic. Diagnosis of neutropenic enterocolitis continues to be a challenge, as patients typically present with nonspecific gastrointestinal tract symptoms. Neutropenia and computed tomographic scan findings are useful adjuncts in diagnosing neutropenic enterocolitis. Timely conservative treatment frequently allows resolution of neutropenic enterocolitis without operation.

Adult↗

PubMed1998

Variable TE gradient and spin echo sequences for in vivo MR microscopy of short T2 species.

Collagen-rich tissues such as skin or fibrous cartilage have very short T2 and thus, in order to be visible, demand a commensurate reduction in echo time. Whereas short echo time for imaging of humans is straightforward at large fields of view with currently available whole body gradient hardware, the problem is more challenging in the microscopic resolution regime (<100 microm). In this work a simple approach consisting of shortening the echo time dynamically toward the lower spatial frequencies is described for three-dimensional partial flip-angle gradient and spin-echo sequences. Microimages obtained in vivo at 50 microm resolution on a 1.5 T whole body scanner are shown to afford a signal-to-noise gain of over 100% in the dermis of the human skin. A point-spread function analysis indicates that the variable echo time gradient-echo sequence produces a unique not previously reported off-resonance artifact in the phase-encoding direction. The artifact results from the phase modulation occurring during the variable echo time and can manifest as both blurring and intensity fluctuations, as well as shifts of boundaries in the phase-encoding direction. However, for the on-resonance condition, the images are free from these artifacts and exhibit significantly improved signal-to-noise ratio.

Artifacts↗

PubMed1998

Measurement of R'2 in the presence of multiple spectral components using reference spectrum deconvolution.

A method is described for measuring R'2, the RF reversible contribution to the effective transverse relaxation rate in yellow trabecular marrow, as a means to evaluate trabecular bone structure and density. The method exploits the similarity in spectral composition of the marrow and fat in subcutaneous tissue. Under these conditions the gradient echo envelope of the marrow signal can be regarded as a convolution of a function describing the bone marrow intravoxel line broadening (R'2) with a function expressing chemical shift modulation, which is obtained from the echo envelope of the subcutaneous fat signal in a reference region. Simple division of each of a series of echoes by the reference signal is shown to afford a smooth decay which can be fitted to a model to extract R'2. The method has been evaluated in the upper femur of test subjects and a strong correlation of the thus derived R'2 values with those obtained by the GESFIDE technique is demonstrated. The close correspondence in spectral composition of proximal femur marrow and subcutaneous fat is further illustrated by means of localized spectroscopy. The major potential error source is global inhomogeneity in the reference region which can lead to an underestimation of the demodulation-derived R'2.

Absorptiometry, Photon↗

PubMed1998

Absence of 185delAG mutation of the BRCA1 gene and 6174delT mutation of the BRCA2 gene in Ashkenazi Jewish men with prostate cancer.

Epidemiological studies have demonstrated a clustering of breast and prostate cancers in some families. Moreover, there is an increase in the number of cases of prostate cancer in families with inherited mutations of the breast cancer susceptibility gene BRCA1. We assessed the role of BRCA1 and BRCA2 in prostate cancer. We tested for the BRCA1 185delAG frameshift mutation, found in 0.9% of Ashkenazi Jews, and the BRCA2 6174delT mutation, found in 1% of Ashkenazi Jews, in Ashkenazi Jewish men with prostate cancer. We studied 60 Ashkenazi men with prostate cancer. A family history was obtained by interview or a self-report questionnaire. Histological confirmation of diagnosis was obtained for all subjects. Ethnic background was confirmed for all subjects by self-report or interview. Mutations of BRCA1 and BRCA2 were detected by amplification of lymphocyte DNA from peripheral blood according to standard polymerase chain reaction (PCR) and dot blot procedures. Patients' ages ranged from 55 to 80 years (mean +/- s.d. 70 +/- 5.25). There were six men with a family history of prostate cancer; three of these had a father with prostate cancer. Five of the men had a family history of breast cancer, in a mother, a sister or an aunt. None of the men had a family history of both breast and prostate cancer. None of the 60 men carried the 185delAG BRCA1 or 6174delT BRCA2 mutations. Of 268 Ashkenazi Jewish women with sporadic breast cancer, tested in an unrelated study, 16 carried either the 185delAG mutation of BRCA1 or the 6174delT mutation of BRCA2. There was a significant difference in the incidence of the BRCA1 and BRCA2 mutations in the breast and prostate cancer cases (P = 0.05, two-tailed Fisher's exact test). The contribution of germline BRCA1 and BRCA2 mutations to prostate cancer incidence is probably small and could be limited to specific subgroups.

Aged↗

PubMed1998

Effects of acanthoic acid on TNF-alpha gene expression and haptoglobin synthesis.

Tumour necrosis factor-alpha (TNF-alpha) is a major pro-inflammatory cytokine inducing the synthesis and release of many inflammatory mediators. It is involved in immune regulation, autoimmune diseases, and inflammation. Our previous study demonstrated that acanthoic acid, (-)-pimara-9(11), 15-dien-19-oic acid, a pimaradiene diterpene isolated from Acanthopanax koreanum, inhibited TNF-alpha production. To extend our understanding of inhibitory effects of acanthoic acid on TNF-alpha production, its effects on TNF-alpha gene expression was tested. Based on the results from RT-PCR and promoter analysis of TNF-alpha, it was found that acanthoic acid suppressed TNF-alpha gene expression. But the same concentration of acanthoic acid had no effect on IL-6 gene expression. Haptoglobin is an acute phase protein which is induced by TNF-alpha. When liver cells were treated with acanthoic acid, haptoglobin synthesis was blocked by acanthoic acid. These data confirmed that acanthoic acid inhibited gene expression and biological function of TNF-alpha.

Anti-Inflammatory Agents, Non-Steroidal↗

PubMed1998

Effects of intrathecal neostigmine, bupivacaine, and their combination on sympathetic nerve activity in rats.

BACKGROUND: Intrathecal injection of local anesthetic agents is associated frequently with hypotension. Conversely, intrathecal administration of neostigmine increases blood pressure by enhancing the accumulation of acetylcholine in the spinal cord. The current study examined directly the interaction of intrathecal injection of bupivacaine and neostigmine on splanchnic sympathetic efferent nerve activity. METHODS: Experiments were performed in rats with intrathecal catheters implanted for the long-term. Rats were anesthetized with ketamine (40 mg/kg, intramuscularly) and alpha-chloralose (60 mg/kg, intraperitoneally). The skin incision sites were infiltrated with 1% lidocaine. Sympathetic efferent activity was recorded from the left greater splanchnic nerve. Sympathetic nerve activity was measured continuously before and after intrathecal injection of saline, 430 nmol (140 microg) of bupivacaine, 25 nmol (7.6 microg) of neostigmine, and a combination of bupivacaine and neostigmine all in volumes of 5 microl. Each group consisted of six animals. RESULTS: Compared with baseline nerve activity, intrathecal injection of neostigmine increased splanchnic sympathetic nerve activity significantly by (mean +/- SEM) 112 +/- 29% after an onset latency of 6.8 +/- 0.9 min. In contrast, bupivacaine decreased splanchnic nerve activity significantly (-65 +/- 13%) after a latency of 3.3 +/- 0.5 min after intrathecal administration. Similar to the effect of saline, intrathecal coadministration of bupivacaine and neostigmine did not alter the splanchnic sympathetic nerve activity significantly. CONCLUSIONS: The current study provides electrophysiologic evidence that intrathecal injection of neostigmine increases whereas bupivacaine decreases sympathetic nerve activity. Further, addition of neostigmine effectively counteracts the inhibitory effect of spinal bupivacaine on the sympathetic nerve activity.

Anesthetics, Local↗

PubMed1998

Spinal nitric oxide mediates antinociception from intravenous morphine.

INTRODUCTION: Spinal nitric oxide (NO) is thought in many circumstances to play a pronociceptive role, because spinal injection of NO synthase inhibitors block hypersensitivity after nerve injury and enhance antinociception from spinal opioids. Conversely, intravenous injection of morphine has been demonstrated to activate descending noradrenergic pathways and to increase spinal synthesis of NO. This study examined the role of spinal NO in antinociception produced by intravenously administered morphine. METHODS: Polyethylene catheters were inserted with tips in the lumbar intrathecal space and in a jugular vein in male rats. Antinociception in response to intravenous injection of morphine was determined by latency to withdrawal of the hind paw from a heat source. Animals received an intrathecal injection of saline, an alpha2-adrenergic antagonist (idazoxan), a muscarinic antagonist (atropine), two NO synthase inhibitors, or an NO scavenger after intravenously administered morphine. RESULTS: Intravenously administered morphine produced dose-dependent antinociception, which was stable for 45 min and unaffected by intrathecally administered saline or atropine injection. In contrast, idazoxan, each of the NO synthase inhibitors, and the NO scavenger produced dose-dependent attenuation of intravenously administered morphine-induced antinociception. DISCUSSION: These results confirm a spinal alpha2-adrenergic mechanism of antinociception from intravenously administered morphine, consistent with morphine's activation of descending noradrenergic pathways. Further, these data suggest that spinal NO mediates antinociception produced by intravenous morphine.

Adrenergic alpha-Antagonists↗

PubMed1998

Cancellous bone volume and structure in the forearm: noninvasive assessment with MR microimaging and image processing.

PURPOSE: To develop and apply a method for the derivation of cancellous bone architectural parameters from in vivo magnetic resonance (MR) images of the distal radius and to evaluate these parameters as predictors of vertebral fracture status in osteopenia. MATERIALS AND METHODS: MR images (137 x 137 x 500-micron3 voxel size) were acquired with a three-dimensional partial flip-angle spin-echo pulse sequence in the distal radius of 36 women. Subjects were classified as healthy or with osteoporosis on the basis of vertebral deformity and bone mineral density (BMD). Images rated as of adequate quality in 20 subjects were processed with a method that is applicable in the limited spatial resolution regime. The method relies on histogram deconvolution to obviate binary segmentation. Cancellous bone structure was treated as a quasi-regular lattice and analyzed with spatial autocorrelation, yielding parameters that quantify intertrabecular spacing, contiguity, and a measure of longitudinal alignment called tubularity. RESULTS: Whereas neither BMD nor any of the structural parameters individually correlated significantly with vertebral deformity fraction, a simple function that involved tubularity and longitudinal spacing predicted deformity fraction well (r = .78, P < .005). CONCLUSION: Histomorphometric parameters characterizing cancellous bone in the distal radius can be derived from in vivo MR microimages and are predictive of vertebral deformity.

Absorptiometry, Photon↗

PubMed1998

A traumatic pseudoaneurysm of the superficial temporal artery.

Pseudoaneurysm arising from the superficial temporal artery (STA) is very rare and is most commonly caused by blunt trauma. Most pseudoaneurysms of the STA usually present as a painless pulsating mass, with concomitant symptoms according to location, and their size may rapidly increase. The treatment of choice is ligation and resection. We present a case of pseudoaneurysm arising from STA after a penetrating injury caused by broken glass. We describe the history, findings of physical examination, Doppler sonography, angiography, histopathology, and the outcome of treatment. We also include a brief review of this condition.

Aneurysm, False↗

PubMed1998

New architectural parameters derived from micro-MRI for the prediction of trabecular bone strength.

This article reviews recent progress in magnetic resonance microimaging of cancellous bone in vitro and in vivo from the perspective of the authors' laboratory. It is shown that in particular in vivo the key technical prerequisites to satisfy are: (i) achieving sufficient signal-to-noise ratio (SNR) to allow for adequate spatial resolution; (ii) the image processing algorithms have to be robust enough to provide accurate structural information in the limited spatial resolution regime, i.e., in the presence of inevitable partial volume blurring and noise. The practical lower limit of voxel size in vivo was found to be about 6 x 10(-3) mm3 in the radius, and about 10(-4) mm3 for small specimens in vitro with state-of-the-art equipment and scan times of 10 and 30 minutes, resp., and SNR approximately 10. Finally, data are presented highlighting the potential of these methods for predicting the bone's elastic modulus in vitro and fracture risk in vivo.

Algorithms↗

PubMed1997

Crystal structure of carboxylesterase from Pseudomonas fluorescens, an alpha/beta hydrolase with broad substrate specificity.

BACKGROUND: A group of esterases, classified as carboxylesterases, hydrolyze carboxylic ester bonds with relatively broad substrate specificity and are useful for stereospecific synthesis and hydrolysis of esters. One such carboxylesterase from Pseudomonas fluorescens is a homodimeric enzyme, consisting of 218-residue subunits. It shows a limited sequence similarity to some members of the alpha/beta hydrolase superfamily. Although crystal structures of a number of serine esterases and lipases have been reported, structural information on carboxylesterases is very limited. This study was undertaken in order to provide such information and to understand a structural basis for the substrate specificity of this carboxylesterase. RESULTS: In this study, the crystal structure of carboxylesterase from P. fluorescens has been determined by the isomorphous replacement method and refined to 1.8 A resolution. Each subunit consists of a central seven-stranded beta sheet flanked by six alpha helices. The structure reveals the catalytic triad as Ser 114-His 199-Asp 168. The structure of the enzyme in complex with the inhibitor phenylmethylsulfonyl fluoride has also been determined and refined to 2.5 . The inhibitor is covalently attached to Ser 114 of both subunits, with the aromatic ring occupying a hydrophobic site defined by the aliphatic sidechains of Leu23, Ile58, Ile70, Met73 and Val170. No large structural changes are observed between the free and inhibitor-bound structures. CONCLUSIONS: Carboxylesterase from P. fluorescens has the alpha/beta hydrolase fold and the Ser-His-Asp catalytic triad. The active-site cleft in each subunit is formed by the six loops covering the catalytic serine residue. Three of the active-site loops in each subunit are involved in a head-to-head subunit interaction to form a dimer; it may be these extra structural elements, not seen in other esterases, that account for the inability of carboxylesterase to hydrolyze long chain fatty acids. As a result of dimerization, the active-site clefts from the two subunits merge to form holes in the dimer. The active-site clefts are relatively open and thus the catalytic residues are exposed to the solvent. An oxyanion hole, formed by nitrogen atoms of Leu23 and Gln115, is present in both the free and inhibitor-bound structures. An open active site, as well as a large binding pocket for the acid part of substrates, in P. fluorescens carboxylesterase may contribute to its relatively broad substrate specificity.

Anions↗

PubMed1997

Crystal structure of thermostable alpha-amylase from Bacillus licheniformis refined at 1.7 A resolution.

alpha-Amylases (alpha-1,4-glucan-4-glucanohydrolase, E.C.3.2.1.1) catalyze the cleavage of alpha-1, 4-glucosidic linkages of starch components, glycogen, and various oligosaccharides. Thermostable alpha-amylases from Bacillus species are of great industrial importance in the production of corn syrup or dextrose. Thermostable alpha-amylase from Bacillus licheniformis, a monomeric enzyme with molecular mass of 55,200 Da (483 amino acid residues), shows a remarkable heat stability. This enzyme provides an attractive model for investigating the structural basis for thermostability of proteins. The three-dimensional structure of thermostable alpha-amylase from Bacillus licheniformis has been determined by the multiple isomorphous replacement method of X-ray crystallography. The structure has been refined to a crystallographic R-factor of 19.9% for 58,601 independent reflections with F0 > 2 sigma F0 between 8.0 and 1.7 A resolution, with root mean square deviations of 0.013 A from ideal bond lengths and 1.72 degrees from ideal bond angles. The final model consists of 469 amino acid residues and 294 water molecules. Missing from the model are the N- and C-termini and the segment between Trp182 and Asn192. Like other alpha-amylases, the polypeptide chain folds into three distinct domains. The first domain (domain A), consisting of 291 residues (from residue 3 to 103 and 207 to 396), forms a (beta/alpha)8-barrel structure. The second domain (domain B), consisting of residues 104 to 206, is inserted between the third beta-strand and the third alpha-helix of domain A. The third C-terminal domain (domain C), consisting of residues 397 to 482, folds into an eight-stranded antiparallel beta-barrel. Neither calcium ion nor chloride ion is located near the active site. This study reveals the architecture of the thermostable alpha-amylase from Bacillus licheniformis. By homology with other alpha-amylases, important active site residues can be identified as Asp231, Glu261, and Asp328, which are all located at the C-terminal end of the central (beta/alpha)8-barrel. Since many of the stabilizing and destabilizing mutations obtained so far fall in domain B or at its border, this region of the enzyme appears to be important for thermostability. The factors responsible for the remarkable thermostability of this enzyme may be increased ionic interactions, reduced surface area, and increased packing interactions in the interior.

Amino Acid Sequence↗

PubMed1997

The crystal structure of a triacylglycerol lipase from Pseudomonas cepacia reveals a highly open conformation in the absence of a bound inhibitor.

BACKGROUND: . Lipases, a family of enzymes which catalyze the hydrolysis of triglycerides, are widely distributed in many organisms. True lipases are distinguished from esterases by the characteristic interfacial activation they exhibit at an oil-water interface. Lipases are one of the most frequently used biocatalysts for organic reactions performed under mild conditions. Their biotechnological applications include food and oil processing and the preparation of chiral intermediates for the synthesis of enantiomerically pure pharmaceuticals. Recent structural studies on several lipases have provided some clues towards understanding the mechanisms of hydrolytic activity, interfacial activation, and stereoselectivity. This study was undertaken in order to provide structural information on bacterial lipases, which is relatively limited in comparison to that on the enzymes from other sources. RESULTS: . We have determined the crystal structure of a triacylglycerol lipase from Pseudomonas cepacia (PcL) in the absence of a bound inhibitor using X-ray crystallography. The structure shows the lipase to contain an alpha/beta-hydrolase fold and a catalytic triad comprising of residues Ser87, His286 and Asp264. The enzyme shares several structural features with homologous lipases from Pseudomonas glumae (PgL) and Chromobacterium viscosum (CvL), including a calcium-binding site. The present structure of PcL reveals a highly open conformation with a solvent-accessible active site. This is in contrast to the structures of PgL and PcL in which the active site is buried under a closed or partially opened 'lid', respectively. CONCLUSIONS: . PcL exhibits some structural features found in other lipases. The presence of the Ser-His-Asp catalytic triad, an oxyanion hole, and the opening of a helical lid suggest that this enzyme shares the same mechanisms of catalysis and interfacial activation as other lipases. The highly open conformation observed in this study is likely to reflect the activated form of the lipase at an oil-water interface. The structure suggests that the interfacial activation of bacterial lipases involves the reorganization of secondary structures and a large movement of the lid to expose the active site. This is similar to the mechanism described for other well characterized fungal and mammalian lipases.

Amino Acid Sequence↗

PubMed1997

In vivo MR microscopy of the human skin.

The requirements for imaging the skin are dictated by the organ's layered structure, which extends only a few millimeters from the surface and thus demands extremely high resolution in this direction. While less critical, resolution in the remaining two dimensions determines whether the skin's accessory structures can be resolved. The problem is compounded by short transverse relaxation times, in particular of the dermis, the structure of most clinical interest. In this work images of the normal human skin were obtained in vivo at voxel sizes as small as 19 x 78 x 800 microm3, by means of customized 3D gradient and partial flip-angle spin-echo pulse sequences and very small transmit/receive coils on a 1.5T clinical imager equipped with high-power whole-body gradients. Structures resolved include hair follicles and the sublayers of the dermis. The very short time constant for the major component (91%) for transverse relaxation in the dermis (T2* approximately 10 ms) suggests the potential of substantial gains in achievable signal-to-noise ratio by shortening the echo time.

Adipose Tissue↗

PubMed1997

A single-scan imaging technique for measurement of the relative concentrations of fat and water protons and their transverse relaxation times.

A two-component chemical-shift-imaging technique is described from which fat and water images can be obtained in a single scan and in the presence of an inhomogeneous field. In addition, the method provides transverse relaxation rates R2 and R2' separately for each of the spectral components. The method is a combination and extension of the GESFIDE [gradient echo sampling of FID and echo, J. Ma and F. W. Wehrli, J. Magn. Reson. B 111, 61 (1996)] and the multipoint Dixon techniques. It is based on sampling the descending and ascending portions of a Hahn spin echo with a train of gradient echoes which are spaced at one-half of the chemical-shift modulation period. Processing of the complex echo data, involving an automated phase unwrapping algorithm, affords relative amplitudes and transverse relaxation rates of the two spectral components. An additional benefit of the method is its superior signal-to-noise ratio resulting from echo summation. Applications targeted and illustrated involve MRI osteodensitometry of trabecular bone in the presence of varying fractions of hematopoietic and fatty bone marrow.

Adult↗

PubMed1997

Effects of single and repeated administration of sulthiame on amygdaloid kindled seizures in rats.

In this study, we assessed the anti-convulsive effects of sulthiame (SUL) in amygdaloid (AM) kindled rats. Electrodes were implanted into the left AM of adult male Wistar rats. The animals were kindled at the after-discharge (AD) threshold. Upon completion of kindling, a generalized seizure triggering threshold was determined. The drugs were administered intraperitoneally in rats which reproducibly exhibited generalized convulsions at the near-threshold stimulation. Single administration of SUL (25-200 mg; n = 7-9) reduced the forelimb clonus (FCL) duration, but only the highest dose significantly regressed the secondarily generalized convulsion. During repeated administration of SUL, 50 mg/kg for 8 days, FCL duration was significantly alleviated until the fifth treatment day. With the dose of 200 mg/kg, significant suppression of secondary generalization was noted only until the second test day. On the other hand, significant reductions of FCL and AD duration were preserved afterwards. The anti-convulsive effects of SUL indicated in this study were not comparable to those of other standard anti-epileptic drugs reported from our laboratory.

Amygdala↗

PubMed1997

Acute Myelitis after hepatitis B vaccination.

We report a case of myelitis after plasma-derived hepatitis B vaccination. The patient was a 31-year-old man who presented with progressive sensory symptoms in extremities that developed 2 weeks after a third vaccination. MRI of the cervicothoracic region revealed swelling and T2 high signal at the level of C4 to C5 cord, and isolated enhancement in the posterior columns between C4 and C5 cord. The significance of MRI findings and HLA haplotype of the patient will be briefly discussed.

Acute Disease↗

PubMed1996

Refined structure of the chitinase from barley seeds at 2.0 a resolution.

Chitinase from barley seeds is a monomeric enzyme with 243 amino-acid residues and it plays a role as a defense protein. Its structure, previously determined at 2.8 A resolution by multiple isomorphous replacement method, is mainly alpha-helical [Hart, Monzingo, Ready, Ernst & Robertus, (1993). J. Mol. Biol. 229, 189-193]. The crystallization and preliminary X-ray data of the same enzyme in a different crystal form has been reported independently [Song, Hwang, Kim & Suh, (1993). Proteins, 17, 107-109}, the asymmetric unit of which contains two chitinase molecules. As a step toward understanding the general principles of catalysis, reported here is the structure of chitinase from barley seeds in this crystal form, as determined by molecular replacement and subsequently refined at 2.0 A resolution, with incorporation of partial data to 1.9 A (R factor of 18.9% for 31 038 unique reflections with F(o)> 2sigma(F) in the range 8.0-1.9 A). The r.m.s. deviations from ideal stereochemistry are 0.013 A for bond lengths and 1.32 degrees for bond angles. A superposition of the two independent molecules in the asymmetric unit gives an r.m.s. difference of 0.55 A for all protein atoms (0.43 and 0.74 A for main-chain and side-chain atoms, respectively). When the refined model of each chitinase molecule in the asymmetric unit is superposed with the starting model, the r.m.s. difference for all shared protein atoms is 0.99 A for molecule 1 and 0.85 A for molecule 2, respectively. Through a sequence comparison with homologous plant chitinases as well as a structural comparison with the active sites of other glycosidases, key catalytic residues have been identified and the active site has been located in the three-dimensional structure of the barley chitinase. The present structure, refined at an effective resolution of 2.0 A with incorporation of partial data to 1.9 A, represents a significant improvement in resolution compared to the previously reported model. The improved resolution has enabled the location of solvent atoms, including water molecules near the catalytic residues, in addition to the positioning of protein atoms with greater accuracy.

Journal Article↗