• The Korean Journal of Zoology
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• v.32 no.2
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• pp.134-141
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• 1989

The present investigation aims at elucidating a possible mechanism of heat inactivation of SCK ceils by comparing the kinetics of cell lethality and protein degradation in the presence of heat protector or heat sensitizer. The effect of heat sensitizer and protector was exhibited in both cell survival and protein degradation kinetics, the magnitude of the effect being much profound for the protector compared to the sensitizer. A conclusion to he drawn from the present experiment is that there is no direct correlation between cell lethality and protein degradation. Rather, protein degradation, which might occur in the membrane, causes cell inactivation indirectly, possibly by altering the cellular environment. Accordingly, further studies are needed to get insight into the mechanism of cell inactivation by hyperthermia.

• BMB Reports
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• v.31 no.3
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• pp.258-263
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• 1998

Acetolactate synthase (ALS) is the common enzyme in the biosynthetic pathways leading to leucine, valine, and isoleucine. Tobacco ALS was expressed in E. coli and purified to homogeneity. The recombinant tobacco ALS was inactivated by thiol-specific reagents, N-ethylmaleimide (NEM) and 5,5'-dithio-bis-(2-nitrobenzoic acid) (DTNB). Inactivation of the ALS by NEM followed pseudo-first order kinetics and was first order with respect to the modifier. The substrate pyruvate protected the enzyme against the inactivation by NEM and DTNB. Extrapolation to complete inactivation of the enzyme by DTNB showed modification of approximately 2 out of 4 total cysteinyl residues (or 2 cysteinyl and 1 cysteinyl residues), with approximately 1 residue protected by pyruvate. The tobacco ALS was also inactivated by the tryptophanspecific reagent, N-bromosuccinimide (NBS), and was similarly protected by pyruvate. The kinetics of the inactivation was first-order with respect to NBS. The present data suggest that cysteinyl and tryptophanyl residues play a key role in the catalytic function of the enzyme.

• Microbiology and Biotechnology Letters
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• v.25 no.2
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• pp.173-177
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• 1997

Glycerol-3-phosphate cytidylyltransferase from Bacillus subtilis was modified with various chemical modifiers to determine the active sites of the enzyme. Treatment of the enzyme with group-specific reagents diethylpyrocarbonate, N-bromosuccinimide, or carbodiimide resulted in complete loss of enzyme activity, which shows histidine, tryptophan, and glutamic acid or aspartic acid residues are at or near the active site. In each case, inactivation followed pseudo first-order kinetics. Inclusion of glycerol-3-phosphate and/or CTP prevented the inactivation, indicating the presence of tryptophan and glutamic acid or aspartic acid residues at the substrate binding site. Analysis of kinetics of inactivation showed that the loss of enzyme activity was due to modification of a two histidine residues, single tryptophan residue, and two glutamic acid or aspartic acid residues.

• Journal of Korean Society of Water and Wastewater
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• v.33 no.5
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• pp.379-388
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• 2019

Chlorination and UV illumination are being widely applied to inactivate a number of pathogenic microbials in the environment. Here, we evaluated the inactivation efficiency of individual and combined treatments of chlorination and UV under various aqueous conditions. UV dosage was required higher in waste water than in phosphate buffer to achieve the similar disinfecting efficiency. Free chlorine generated by electrolysis of waste water was abundant enough to inactivate microbials. Based on these, hybrid system composed of sequential treatment of electrolysis-mediated chlorination and UV treatment was developed under waste water conditions. Compared to individual treatments, hybrid system inactivated bacteria (i.e., E. coli and S. typhimurium) and viruses (i.e., MS-2 bacteriophage, rotavirus, and norovirus) more efficiently. The hybrid system also mitigated the photo re-pair of UV-driven DNA damages of target bacteria. The combined results suggested the hybrid system would achieve high inactivation efficiency and safety on various pathogenic microbials in wastewater.

• Food Science of Animal Resources
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• v.29 no.3
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• pp.310-316
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• 2009

In this study, the influence of pressure assisted mild thermal inactivation (PAMTI) on E. coli ATCC 10536 was examined at 200 MPa and temperature range of $20-50^{\circ}C$. Inactivation rate significantly increased (p<0.05) as temperature and time increased at 200 MPa. The maximum inactivation (7.91 log reduction) was obtained at $50^{\circ}C$ for 30 min under 200 MPa, which meant the complete inactivation of E. coli ATCC 10536. Inactivation kinetics were evaluated with the first order inactivation rate (k), activation energy ($E_a$), thermal death time (TDT), and z value. Kinetic parameters were significantly (p<0.05) influenced by variation temperature of PAMTI. In this study, the synergistic effect of pressure and temperature were found in the inactivation of E. coli ATCC 10536 through PAMTI.

• BMB Reports
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• v.30 no.2
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• pp.113-118
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• 1997

Aspartase from Hafnia alvei was inactivated by N-ethylmaleimide (NEM) and 5,5' -Dithiobis-(2-znitrobenzoic acid) (DTNB) following pseudo-first order kinetics. Their apparent reaction orders were 0.83 and 0.50 for NEM and DTNB modifications, respectively, indicating that inactivation was due to a sulfhydryl group in the active site of aspartase and participation of the sulfhydryl group in an essential step in the catalytic reaction. When aspartase was modified by DTNB, the enzyme activity was restored by dithiothreitol treatment, indicating that cysteine residuetsl islarel possibly at or near the active site. The pH-dependence of the inactivation rate by NEM suggested that an amino acid residue having pK value of 8.3 was involved in the inactivation. When aspartase was incubated with NEM and L-aspartate together, L-aspartate markedly protected the enzyme from inactivation by NEM, but the other reagents used did not.

• Applied Microscopy
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• v.11 no.1
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• pp.29-38
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• 1981

Bacteriophage f2 were treated with ozone at various concentrations for 20 minutes. The inactivation kinetics of f2 phage were examined during ozonation. In order to study the mode of action of ozone on the phage f2, absorption of the phage to the host pili was meassured by utilyzing radioactivity of tritium incorporated into the phage RNA. Sucrose density gradient analysis and electron microscopy were also used to prove the mechanism of ozone inactivation of the phage. Strucural proteins of the phage were broken by ozonation into many protein subunits. The extent of phage breakage was proportional to ozone concentration and reaction time. Percent decrease of the phage absorption to the host pili was coincident with the rate of ozone inactivation of the phage. Ozone inactivation of bacteriophage f2 was shown to be caused by the breakage of the structural protein and blockage of the phage absorption to the host pili.

• The Korean Journal of Food And Nutrition
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• v.34 no.1
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• pp.26-35
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• 2021

Myrosinases (thioglucosidases) catalyze the hydrolysis of a class of compounds called glucosinolates, of which the aglycones show various biological functions. It is often necessary to minimize the loss of myrosinase activity during thermal processing of cruciferous vegetables. Myrosinase was isolated from a popular spice, white mustard (Sinapis alba), and its thermal inactivation kinetics was investigated. The enzyme was extracted from white mustard seeds and purified by a sequential processes of ammonium sulfate fractionation, Concanavalin A-Sepharose column chromatography, and gel permeation chromatography. At least three isozymes were revealed by Concanavalin A-Sepharose column chromatography. The purity of the major myrosinase was examined by native polyacrylamide gel electrophoresis and on-gel activity staining with methyl red. The molecular weight of the major enzyme was estimated to be 171 kDa. When the consecutive step model was used for the thermal inactivation of the major myrosinase, its inactivation energy was 44.388 kJ/mol for the early stage of destruction and 32.019 kJ/mol for the late stage of destruction. When the distinct two enzymes model was used, the inactivation energy was 77.772 kJ/mol for the labile enzyme and 95.145 kJ/mol for the stable enzyme. The thermal inactivation energies lie within energy range causing nutrient destruction on heating.

• Food Engineering Progress
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• v.13 no.2
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• pp.122-129
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• 2009

Ultraviolet (UV) is widely used as a sterilizing agent in restaurants and catering facilities in Korea. Efficacy of UV sterilizers (UVS) was investigated against E. coli on the inner bottom of stainless steel cups. UV intensity on the bottom of cups varied widely with the locations of cups in UVS, showing higher values at center while lower values at outskirts. The deviations in UV intensity were remarkable on top shelf, but alleviated as proceeded to middle and bottom shelves. Inactivation of E. coli was proportional to the UV intensity and treatment time, consequently to UV dose, and showed a pseudo-first-order kinetics with tailing. Initial inactivation rate constants ($K_{1}$) deviated with the locations of the cups, while final inactivation rate constants ($K_{2}$) showed comparable values. An equation for the calculation of the proposed UV treatment time was suggested.

• Food Engineering Progress
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• v.14 no.3
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• pp.202-207
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• 2010

Low-pressure plasmas (LPPs) were generated with different gases such as air, oxygen and nitrogen, and their inactivation effects against Escherichia coli were compared in order to evaluate the potential as a non-thermal microbial disinfection technology. Homogeneous plasmas were generated under low pressure below 1 Torr at gas flow rate of 350 mL/min regardless the types of gases. Temperature increases by LPPs were not detrimental showing less than ${10^{\circ}C}$ and ${25^{\circ}C}$ increases after 5 and 10 min treatments, respectively. The smallest temperature increase was observed with air LPP, and followed by oxygen and nitrogen LPPs. More than 5 log reduction in E. coli was achieved by 5 min LPP treatment but the destruction effect was retarded afterward. The LPP inactivation was represented by a iphasic first order reaction kinetics. The highest inactivation rate constant was achieved in air LPP and followed by oxygen and nitrogen LPPs. The small D-values of the LPP also supported its potentialities as a non-thermal food surface disinfection technology in addition to the substantial microbial reduction of more than 5 logs.