Analysis of the effect of accumulation of amino acid replacements on activity of 3-isopropylmalate dehydrogenase from Thermus thermophilus

A newly selected cold-adapted mutant 3-isopropylmalate dehydrogenase (IPMDH) from a random mutant library was a double mutant containing the mutations I11V and S92F that were found in cold-adapted mutant IPMDHs previously isolated. To elucidate the effect of each mutation on enzymatic activity, I11V and six multiple mutant IPMDHs were constructed and analyzed. All of the multiple mutant IPMDHs were found to be improved in catalytic activity at moderate temperatures by increasing the k(cat) with a simultaneous increase of K(m) for the coenzyme NAD(+). k(cat) was improved by a decrease in the activation enthalpy, DeltaH( not equal). The multiple mutants did not show large reduction in thermal stability, and one of them showed enhanced thermal stability. Mutation from I11 to V was revealed to have a stabilizing effect. Mutants showed increased thermal stability when the mutation I11V was combined. This indicates that it is possible to construct mutants with enhanced thermal stability by combining stabilizing mutation. No additivity was observed for the thermodynamic properties of catalytic reaction in the multiple mutant IPMDHs, implying that the structural changes induced by the mutations were interacting with each other. This indicates that careful and detailed tuning is required for enhancing activity in contrast to thermal stability.

Glucocorticoids and IL-10, but not 6-MP, 5-ASA or sulfasalazine block endothelial expression of MAdCAM-1: implications for inflammatory bowel disease therapy

BACKGROUND

Enhanced MAdCAM-1 (mucosal addressin cell adhesion molecule-1) expression is associated with the aetiology of inflammatory bowel disease, but little is known about MAdCAM-1: regulation, or how inflammatory bowel disease therapies modulate MAdCAM-1.

AIM

To examine how agents currently used to treat inflammatory bowel disease affect MAdCAM-1: induced by tnf-alpha in an in vitro model of inflammatory bowel disease.

METHODS

Endothelial monolayers were pretreated with dexamethasone (DEX): 5-aminosalicylic acid (5-ASA), 6-mercaptopurine (6-MP), sulfasalazine or interleukin-10: (IL-10: prior to TNF-alpha (20 ng/mL), and MAdCAM-1: measured by Western blotting, RT-PCR, EMSA and lymphocyte adhesion assays.

RESULTS

MAdCAM-1: was induced dose- and time-dependently by TNF-alpha on endothelial cells. Either dexamethasone or IL-10: reduced TNF-alpha-induced MAdCAM-1: protein, mRNA and lymphocyte adhesion. However, neither 5-ASA, sulfasalazine nor 6-MP blocked MAdCAM-1 induction.

CONCLUSIONS

Our data indicate that dexamethasone or IL-10 can exert therapeutic activity in inflammatory bowel disease through MAdCAM-1 inhibition. 5-ASA, sulfasalazine and 6-MP, while beneficial in inflammatory bowel disease, do not directly control MAdCAM-1, and are beneficial through inhibition of other inflammatory processes.

Role of nitric oxide in human gastric cancer cells treated with 5-fluorouracil

We examined whether 5-fluorouracil (5-FU) induces nitric oxide (NO) production and evaluated the role of NO in antitumor activity in human gastric cancer cells. MKN-1 gastric cancer cells were treated with the IC50 of 5-FU in the presence of interferon-gamma (IFN-gamma). In addition, s-methylisothiourea (an antagonist of inducible nitric oxide synthase) or anti-TNF-alpha antibody was added to the culture medium. Production of NO was measured by nitrite assay, TNF-alpha was measured by enzyme-linked immunoabsorbent assay, antitumor activity was evaluated by 3-[4,5-dimethylethiazol-2-yl]-2,5-dipheniltetrasolium bromide (MTT) assay. After 5-FU treatment in the presence of IFN-gamma, NO and TNF-alpha were produced and anti-tumor activity was enhanced. In contrast, s-methylisothiourea abolished the antitumor activity of 5-FU treatment. Anti-TNF-alpha antibody inhibited NO production and decreased the antitumor activity. 5-FU induces NO production by gastric cancer cells, and NO participates in antitumor activity in gastric cancer cells. These effects may be mediated by TNF-alpha production.

Effects of angiotensin-(1-7) on forearm circulation in normotensive subjects and patients with essential hypertension

Previous animal studies have shown that angiotensin (Ang)-(1-7) is a biologically active component of the renin-angiotensin system, acting as a vasoactive agent, and may play a role in the blood pressure regulation. There is little information, however, on the effect of Ang-(1-7) on human circulation or the mechanism of its action. To investigate the effect of Ang-(1-7) on forearm circulation and to determine whether this effect is altered in patients with essential hypertension, we measured change in forearm blood flow using venous occlusion plethysmography in response to intra-arterial infusion of Ang-(1-7) (10(-10), 10(-9), and 10(-8) mol/min; for 5 minutes) in normotensive control subjects (n=8) and patients with essential hypertension (n=8). Infusion of Ang-(1-7) significantly increased the forearm blood flow response in a dose-dependent manner in both normotensive control subjects (28.7+/-9.7%, at 10(-8) mol/min; P<0.05) and hypertensive patients (31.8+/-15.2%, at 10(-8) mol/min; P<0.05). The vasodilatory effect of Ang-(1-7) was similar in the two groups. Intra-arterial infusion of N(G)-monomethyl-L-arginine, a nitric oxide synthesis inhibitor, did not alter the forearm blood flow response to Ang-(1-7) in either group. These findings suggest that Ang-(1-7) causes vasodilation in forearm circulation of normotensive subjects and patients with essential hypertension through a pathway that is independent of nitric oxide synthesis.

Vitamin D receptor gene polymorphism is associated with serum total and ionized calcium concentration

Restriction fragment length polymorphisms of the vitamin D receptor gene have recently been reported to be associated with changes in bone mineral density. Alterations in systemic calcium balance and Ca-regulating hormones such as 1,25(OH)2 vitamin D3 and parathyroid hormone have been demonstrated in essential hypertension. We investigated the relationship between polymorphisms of the vitamin D receptor gene and systemic Ca metabolism in patients with essential hypertension and in normotensives. We compared 147 subjects with essential hypertension and 100 normotensive control subjects. The genotype distribution and derived allele frequencies for the vitamin D receptor gene were similar in the two groups (genotype bb/Bb/BB and allele B/b: 60.1/32.6/7.2 and 0.24/0.76 in hypertensives vs. 56.0/36.0/8.0 and 0.26/0.74 in normotensive subjects). Serum concentrations of total Ca in the bb, Bb, and BB groups were, respectively, 4.5+/-0.3 vs. 4.5+/-0.4 vs. 4.4+/-0.5 mmol/l in normotensives and 4.6+/-0.3 vs. 4.6+/-0.4 vs. 4.4+/-0.5 mmol/l in hypertensives. Ionized Ca levels were 1.17+/-0.04 vs. 1.16+/-0.04 vs. 1.15+/-0.04 mmol/l in normotensives and 1.16+/-0.04 vs. 1.16+/-0.04 vs. 1.14+/-0.05 mmol/l in hypertensives, respectively. These results indicate that the BB genotype of the vitamin D receptor gene is associated with lower serum Ca levels but is not a useful predictive marker for the development of essential hypertension in Japanese subjects.

Apoptosis is not increased in myocardium overexpressing type 2 angiotensin II receptor in transgenic mice

To determine whether angiotensin type 2 (AT(2)) receptor stimulation induces apoptosis in cardiomyocytes in vivo, we developed transgenic mice overexpressing the AT(2) receptor in a cardiac-specific manner, using the alpha-myosin heavy-chain promoter. Ten- to 12-week-old male homozygous transgenic mice (n=44) and wild-type mice (n=44) were used. Both transgenic and wild-type mice were given either saline (control), a subpressor dose of angiotensin II (100 ng. kg(-1). min(-1)), a pressor dose of angiotensin II (1000 ng. kg(-1). min(-1)) for 14 days, a pressor dose of angiotensin II for 28 days to investigate the effects of stimulation on both angiotensin type 1 (AT(1)) and AT(2) receptors, the AT(1) antagonist L158809 alone, or a combination of angiotensin II (1000 ng. kg(-1). min(-1)) and L158809 for 14 days to investigate the effects of selective AT(2) receptor stimulation. Apoptosis was analyzed in paraffin-embedded ventricular sections by the terminal deoxynucleotidyl-transferase-mediated dUTP nick-end labeling (TUNEL) technique. In both transgenic and wild-type mice, administration of a subpressor dose of angiotensin II, L158809, or a combination of angiotensin II and L158809 did not significantly affect the tail-cuff blood pressure or heart-to-body weight ratio, whereas administration of a pressor dose of angiotensin II for 14 or 28 days significantly increased blood pressure and the heart-to-body weight ratio. However, there was no statistical difference between the effects of angiotensin II in transgenic and wild-type mice. The number of TUNEL-positive nuclei was approximately 0 to 10 per 100 000 cardiomyocytes, with no difference between transgenic and wild-type mice, regardless of saline infusion or any stimulation. In infarcted canine myocardial tissue sections for positive control, the number of TUNEL-positive nuclei was increased by 13.8 to 19.1 times compared with those in the noninfarcted myocardium. In conclusion, angiotensin II infusion for a period of 28 days failed to induce cardiomyocyte apoptosis regardless of the presence or absence of cardiac AT(2) receptor overexpression. It is unlikely that in mice the AT(2) receptor is a strong signal to induce cardiomyocyte apoptosis in vivo.

Poly ADP ribose-polymerase inhibitors prevent the upregulation of ICAM-1 and E-selectin in response to Th1 cytokine stimulation

We studied the role of poly-ADP-ribose polymerase (PARP) in the mobilization of ICAM-1, VCAM-1, and E-selectin by TNF-alpha and IL-1beta in cultured human endothelial cells. Enzyme linked immunosorbent analysis (ELISA) was used to assess if ICAM-1, VCAM-1, and E-selectin were expressed at the cell surface, and if PARP inhibition (using the selective PARP inhibitor GPI 6150) blocked the induced expression. Endothelial cell adhesion molecule expression was evaluated at 4 and at 24 h after cytokine stimulation. At 4 h ICAM-1 and E-selectin, but not VACM-1, were stimulated by both IL-1beta and TNF-alpha. Blocking PARP via GPI 6150 only affected TNF-alpha induced E-selectin expression at 4 hours. ICAM-1, VCAM-1, and E-selectin expression were all stimulated by both IL-1beta and TNF-alpha in the 24 h assays. PARP inhibition with GPI 6150 blocked the IL-1beta mediated stimulation of both ICAM-1 and E-selectin expression, and blocked TNF-alpha stimulation of ICAM-1 expression at 24 h. These experiments suggest that specific PARP inhibition may provide a novel method of controlling leukocyte dependent inflammation through the reduction of ICAM-1 and E-selectin expression in endothelial cells in response to cytokines.

Non-dipper phenomenon in essential hypertension is related to blunted nocturnal rise and fall of sympatho-vagal nervous activity and progress in retinopathy

Although the relation between the blunted nocturnal decline in blood pressure and target organ damages is well established, the mechanism underlying these results has not been clarified. We investigated the relationship among heart rate variability, nocturnal change in blood pressure and the severity of cardiac and extracardiac target organ damages caused by essential hypertension. We studied 52 Japanese inpatients with essential hypertension (24 men and 28 women; mean age, 49+/-3 years). After a stabilization period of 1 week, ambulatory blood pressure monitoring (ABPM) and 24-h ECG monitoring were performed and analyzed. The non-dipper subjects were defined as those whose nocturnal decrease of mean BP was < 10% of daytime blood pressure (BP). The sex, age, body mass index. duration of hypertension, and 24-h BP were similar in dipper (n = 34) and non-dipper (n = 18) patients. The left ventricular mass index (LVMI) was significantly higher and the degree of hypertensive retinopathy was significantly worse in the non-dipper patients than that of the dipper patients. In the non-dipper patients, indexes of time-domain analysis such as the sum of differences between adjacent RR intervals (NNDrms), the number of pairs of adjacent RR intervals differing by more than 50 ms in the entire recording (RR 50) were significantly lower than that of the dipper patients. Additionally, as for spectral analysis, daytime low frequency/high frequency (LF/HF) was higher and nighttime high frequency (HF) was lower than that of the dipper patients. Independent predictors were the 24-h mean blood pressure (MBP) for left ventricular hypertrophy (LVH), nighttime systric BP (SBP) for progress in retinopathy and duration of hypertension for proteinuria. In conclusion, decrease in parasympathetic nervous function and increase in sympathetic nervous function may contribute to occurrence of non-dipper phenomenon, as well as progress in retinopathy.

Ancestral residues stabilizing 3-isopropylmalate dehydrogenase of an extreme thermophile: experimental evidence supporting the thermophilic common ancestor hypothesis

Ancestral amino acid residues were inferred for 3-isopropylmalate dehydrogenase (IPMDH), and were introduced into the enzyme of an extreme thermophile, Sulfolobus sp. strain 7. The thermostability of the mutant enzymes was compared with that of the wild type enzyme. At least five of the seven mutants tested showed higher thermal stability than the wild type IPMDH. The results are compatible with the hyperthermophilic universal ancestor hypothesis. The results also provide a new method for designing thermostable enzymes. The method only relies on the first dimensional structures of homologous enzymes that can be obtained from genetic databases.

Expression of connexin 30 in the developing mouse cochlea

Mutations in the GJB6 gene encoding connexin 30 (Cx30) can cause dominant forms of nonsyndromic deafness. By studying immunohistochemical localization of Cx30 in the mouse cochlea at different ages from 0 to 30 days after birth, we found that the expression of Cx30 is nearly the same as that of Cx26. These findings suggest that as well as Cx26, Cx30 may also contribute to the generation and maturation of endocochlear potential.

Expression of the voltage-dependent chloride channel ClC-3 in human nasal tissue

In the present study, ClC-3, one of the voltage-dependent chloride channels, was identified in human nasal tissue. In situ hybridization and immunohistochemical investigations demonstrated the localization of ClC-3 in the serous acini and ductal portions of submucosal nasal glands, which are the primary source of nasal secretion. Our data suggest that this channel contributes to nasal secretion via chloride transport. Its dysfunction might lead to abnormal nasal secretion in such pathological states as sinusitis.

Effect of the angiotensin-converting enzyme inhibitor imidapril on reactive hyperemia in patients with essential hypertension: relationship between treatment periods and resistance artery endothelial function

OBJECTIVES

The purpose of this study was to evaluate the effects of the angiotensin-converting enzyme (ACE) inhibitor imidapril and the calcium antagonist amlodipine on endothelial function before and after 2, 4, 8, 12, 24 and 48 weeks of treatment.

BACKGROUND

There are limited data on whether and how long endothelial function is improved after initiation of ACE inhibitor treatment and how the grade of endothelial function further progresses after improvement of endothelial dysfunction in patients with essential hypertension.

METHODS

The forearm blood flow (FBF) was measured in 25 patients with essential hypertension and in 25 normotensive subjects by using strain-gauge plethysmography during reactive hyperemia (RH) (280 mm Hg for 5 min) and after sublingual administration of nitroglycerin (NTG, 0.3 mg).

RESULTS

The FBF of patients with essential hypertension during RH was significantly less than that of normotensive subjects. The increase in FBF after sublingual NTG was similar in both groups. Both imidapril (n = 13) and amlodipine (n = 12) significantly reduced systolic blood pressure and diastolic after eight weeks of treatment from the pretreatment values. Forearm vascular resistance was significantly decreased after two weeks of treatment. Imidapril significantly augmented RH after 12 weeks of treatment from the pretreatment values (31.6 +/- 5.7 to 38.2 +/- 6.0 m/min per 100 ml tissue, p < 0.05), whereas amlodipine did not alter RH for each treatment period. The ability of imidapril to improve RH was maintained throughout the 48-week treatment period. There was no significant difference in RH at 12, 24 and 48 weeks. The increase in FBF after sublingual administration of NTG was similar in all treatment periods for the two groups. The infusion of NG-monomethyl-L-arginine, a nitric oxide (NO) synthase inhibitor, abolished the enhancement of RH in hypertensive patients treated with imidapril.

CONCLUSIONS

These findings suggest that the ACE inhibitor imidapril augments RH after 12 weeks of treatment in patients with essential hypertension and that this ACE inhibitor-induced augmentation of RH may be due to an increase in NO.

The expression of apoptosis-related proteins in the aged cochlea of Mongolian gerbils

OBJECTIVE

Apoptotic changes have been reported in the aged gerbil cochlea and are speculated to be one of the principal causes of presbyacusis. The objective of the study was to determine the underlying mechanism of apoptotic change in the aged gerbil cochlea.

STUDY DESIGN

Prospective controlled animal study.

METHODS

We examined the tissue distribution of bcl-2, bax, caspase-3p20, and caspase-3p32 using immunohistochemical techniques in the young and aged gerbil cochlea, together with the measurement of the distortion product of otoacoustic emission (DPOAE).

RESULTS

Aged gerbils showed a significant reduction of the DPOAE amplitude as compared with that of the young gerbils, suggesting a disturbance of the auditory function in the aged cochlea. There was a significant decrease in the number of bcl-2-positive cells in the aged gerbils. The expression of bax in the aged group was slightly increased but did not significantly differ from that in the young gerbils. A significantly increased number of caspase-3p20-positive cells was observed in the organ of Corti, spiral ganglion, and lateral wall of cochlea in the aged gerbils as compared with those of the young gerbils. There was no significant difference in the expression levels of caspase-3p32 between the young and aged groups. In the aged cochlea, the degree of deterioration of DPOAE responses was compatible with those of both the reduction of bcl-2 and the activation of caspase-3p20.

CONCLUSION

These data suggest that the suppression of bcl-2 protein expression may lead to apoptosis-induced presbyacusis through activation of caspase-3 in the aged gerbil cochlea.

Influence of natural and synthetic compounds on cell surface expression of cell adhesion molecules, ICAM-1 and VCAM-1

Various natural and synthetic compounds including alkaloids, terpenoids and phenolics were tested for inhibition of the cell surface expression of intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1), both of which are crucial in the regulation of immune response and inflammation. Of 40 compounds tested, two compounds significantly downregulated the expression of VCAM-1 on murine endothelial cells (F-2) and ten compounds that of ICAM-1 on mouse myeloid leukemia cells (M1). Sanguinarine chloride (5) and isoliquiritigenin (13) were capable of lowering the levels of both ICAM-1 and VCAM-1. The structure-activity relationships study on chalcone and flavone derivatives related to 13 suggested that the inhibitory activity of the chalcone derivatives is attributable to the 4-hydroxy group as well as the possible coplanarity between the phenyl ring and the adjacent conjugated ketone.

Cold adaptation of the thermophilic enzyme 3-isopropylmalate dehydrogenase

We have performed random mutagenesis coupled with selection to isolate mutant enzymes with high catalytic activities at low temperature from thermophilic 3-isopropylmalate dehydrogenase (IPMDH) originally isolated from Thermus thermophilus. Five cold-adapted mutant IPMDHs with single-amino-acid substitutions were obtained and analyzed. Kinetic analysis revealed that there are two types of cold-adapted mutant IPMDH: k(cat)-improved (improved in k(cat)) and K(m)-improved (improved in k(cat)/K(m)) types. To determine the mechanisms of cold adaptation of these mutants, thermodynamic parameters were estimated and compared with those of the Escherichia coli wild-type IPMDH. The Delta G(m) values for Michaelis intermediate formation of the k(cat)-improved-type enzymes were larger than that of the T. thermophilus wild-type IPMDH and similar to that of the E. coli wild-type IPMDH. The Delta G(m) values of K(m)-improved-type enzymes were smaller than that of the T. thermophilus wild-type IPMDH. Fitting of NAD(+) binding was improved in the K(m)-improved-type enzymes. The two types of cold-adapted mutants employed one of the two strategies of E. coli wild-type IPMDH: relative destabilization of the Michaelis complex in k(cat)-improved-type, and destabilization of the rate-limiting step in K(m)-improved type mutants. Some cold-adapted mutant IPMDHs retained thermostability similar to that of the T. thermophilus wild-type IPMDH.

Occurrence of D-Amino Acids and a pyridoxal 5'-phosphate-dependent aspartate racemase in the acidothermophilic archaeon, Thermoplasma acidophilum

Free D-amino acid content in some archaea was investigated and D-forms of several amino acids were found in them. In the acidothermophilic archaeon, Thermoplasma acidophilum, the proportion of D-aspartate (D-Asp) to total Asp was as high as 39.7%. Crude extracts of Thermoplasma acidophilum had Asp-specific racemase activity that was pyridoxal 5'-phosphate (PLP)-dependent. The relative insensitivity to a SH-modifying reagent distinguished this activity from those of the PLP-independent Asp racemases found in other hyperthermophilic archaea (Matsumoto, M., et al., J. Bacteriol. 181, 6560-6563 1999). Thus, high levels of d-Asp should be produced by a new type(s) of Asp-specific racemase in Thermoplasma acidophilum, although the function of d-Asp in this archaeon remains unknown.

Thermostabilization of a chimeric enzyme by residue substitutions: four amino acid residues in loop regions are responsible for the thermostability of Thermus thermophilus isopropylmalate dehydrogenase

A chimeric 3-isopropylmalate dehydrogenase, named 2T2M6T, made of parts from an extreme thermophile, Thermus thermophilus, and a mesophile, Bacillus subtilis, was found to be considerably more labile than the T. thermophilus wild-type isopropylmalate dehydrogenase. In order to identify the molecular basis of the thermal stability of the T. thermophilus isopropylmalate dehydrogenase, 11 amino acid residues in the mesophilic portion of the chimera were substituted by the corresponding residues of the T. thermophilus enzyme, and the effects of the side chain substitutions were analyzed by comparing the reaction rate of irreversible heat denaturation and catalytic parameters of the mutant chimeras with those of the original chimera, 2T2M6T. Four single-site mutants were successfully stabilized without any loss of the catalytic function. All these four sites are located in loop regions of the enzyme. Our results strongly suggest the importance of these loop structures to the extreme stability of the T. thermophilus isopropylmalate dehydrogenase.

Quantitative assessment of the pharyngeal airway by dynamic magnetic resonance imaging in obstructive sleep apnea syndrome

Dynamic changes in the pharyngeal airway of patients with obstructive sleep apnea syndrome (OSAS) were evaluated by quantitating the findings of real-time imaging performed during wakefulness and spontaneous sleep by means of dynamic magnetic resonance imaging (MRI). Six patients with OSAS and 3 non-OSAS subjects, selected prospectively and randomly, underwent polysomnography and dynamic MRI. The cross-sectional areas of the soft palate and oropharynx and the anterior-posterior airway dimensions seen during wakefulness and spontaneous sleep were calculated by US National Institutes of Health imaging software. On the basis of a case control study, comparisons were made with age-matched and body mass index-matched obese non-OSAS snorers. Spontaneous sleep caused significant obstruction and narrowing of various sites of the pharyngeal airway in the OSAS patients, but not in the non-OSAS subjects. During wakefulness, the non-OSAS subjects showed no marked narrowing of the pharyngeal airways, whereas a transient but significant narrowing was observed in the OSAS patients. The mean values of both the cross-sectional area and the anterior-posterior diameter at the soft palate were significantly reduced by spontaneous sleep in the OSAS patients. Dynamic MRI in awake OSAS patients shows promise as a routine diagnostic tool for localizing the upper airway collapse for appropriate selection of surgical therapy.

Selection of stabilized 3-isopropylmalate dehydrogenase of Saccharomyces cerevisiae using the host-vector system of an extreme thermophile, Thermus thermophilus

A leuB strain of Thermus thermophilus TTY1, was transformed with a plasmid vector that directed expression of 3-isopropylmalate dehydrogenase (IPMDH) of Saccharomyces cerevisiae encoded by the LEU2 gene. The original strain could not grow at 50 degrees C without leucine, probably because of the low stability of S. cerevisiae IPMDH. The mutants that could grow without leucine were selected at 50 degrees, 60 degrees, 62 degrees, 65 degrees, 67 degrees, and 70 degrees C, step by step. All the mutant strains except for one isolated at 50 degrees C accumulated mutations. Mutations were serially accumulated: Glu255Val, Asn43Tyr, Ala62Thr, Asn110Lys, and Alal 12Val, respectively, at each step. The analyses of residual activity after heat treatment and the denaturation profile as monitored by circular dichroism showed that thermal stability was increased with accumulation of the mutations. The kinetic parameters of most mutant enzymes were similar to those of the wild type. However, some mutant enzymes showed a reverse correlation between stability and activity: the enzymes with a large increase in thermal stability showed lower activity. Although the wild-type enzyme is unstable in the absence of glycerol, the stabilizing effect of glycerol was not observed for all the mutant enzymes containing the Glu255Val substitution, which is assumed to be located at the hydrophobic interface between two subunits.

Quinone profiles of Thermoplasma acidophilum HO-62

Quinones of Thermoplasma acidophilum HO-62 were analyzed by high-performance liquid chromatography, mass spectrometry, and nuclear magnetic resonance. Menaquinone, methionaquinone, and 2-trans and 2-cis forms of thermoplasmaquinone were identified. The relative amount of thermoplasmaquinone increased under anaerobic conditions, and those of menaquinone and methionaquinone increased under aerobic conditions.

Adaptation of a thermophilic enzyme, 3-isopropylmalate dehydrogenase, to low temperatures

Random mutagenesis coupled with screening of the active enzyme at a low temperature was applied to isolate cold-adapted mutants of a thermophilic enzyme. Four mutant enzymes with enhanced specific activities (up to 4.1-fold at 40 degrees C) at a moderate temperature were isolated from randomly mutated Thermus thermophilus 3-isopropylmalate dehydrogenase. Kinetic analysis revealed two types of cold-adapted mutants, i.e. k(cat)-improved and K(m)-improved types. The k(cat)-improved mutants showed less temperature-dependent catalytic properties, resulting in improvement of k(cat) (up to 7.5-fold at 40 degrees C) at lower temperatures with increased K(m) values mainly for NAD. The K(m)-improved enzyme showed higher affinities toward the substrate and the coenzyme without significant change in k(cat) at the temperatures investigated (30-70 degrees C). In k(cat)-improved mutants, replacement of a residue was found near the binding pocket for the adenine portion of NAD. Two of the mutants retained thermal stability indistinguishable from the wild-type enzyme. Extreme thermal stability of the thermophilic enzyme is not necessarily decreased to improve the catalytic function at lower temperatures. The present strategy provides a powerful tool for obtaining active mutant enzymes at lower temperatures. The results also indicate that it is possible to obtain cold-adapted mutant enzymes with high thermal stability.

Laparoscopic surgery using a newly designed suction lifter

The authors describe a simple and available abdominal wall-lift technique for endoscopic surgery that involves a new suction lifter that they designed for laparoscopic surgery. Since July 1998, the authors have used this technique successfully in eight patients with appendicitis, in one patient with a perforated duodenal ulcer, and in one patient with an adenoma of the ascending colon.