Thermal Lability Research Articles

Reduction of CO2 Directed toward Carbon–Carbon Bond Formation

Abstract This paper describes electrochemical reduction of CO2 directed toward carbon–carbon bond formation via metal–CO2 adducts. An electrophilic attack of CO2 to penta-coordinated low valent polypyridyl Ru complexes affords a Ru–η1-CO2 adduct, which is easily converted to Ru–CO species either by an acid-base equilibrium in protic media and oxide transfer to CO2 under aprotic conditions. Two-electron reduction of resultant Ru–CO in protic solutions competitively causes a cleavage of the Ru–CO bond (CO evolution) and formation of a thermally labile Ru–CHO bond. Besides further reduction of the latter to Ru–CH2OH as precursors to CH3OH and HOOCCH2OH, Ru–CHO reacts with CO2 to afford HCOOH with regenerating Ru–CO as the precursor to CO. Thus, the difficulty of multi-electron reduction of CO2 in protic solutions is ascribed to the thermal lability and strong hydride donor character of Ru–CHO. On the other hand, two-electron reduction of Ru–CO in the presence of (CH3)4N+ or CH3I under aprotic conditions produces thermally stable R–C(O)CH3, which works as a precursor to CH3C(O)CH3. Two-electron reduction of M3(μ3-S)2 clusters (M = Co, Rh, Ir) causes an M–M bond cleavage and the nucleophilicity of the μ3-S ligand is also enhanced. As a result, two CO2 molecules reductively activated probably on μ3-S and metal sites undergo the coupling reaction to give oxalate selectively.

Thermometry and calorimetry in the neonate: Recent advances in monitoring and research

Due to its small body size, which in the case of prematurity is associated with increased skin permeability and incomplete brown fat development, the human neonate is highly prone to heat loss. Hence, thermal protection is mandatory to prevent neonatal hypothermia with its adverse metabolic and hemodynamic effects. This is usually attempted by the selection of “thermoneutral” ambient temperatures to maintain core temperature constant without regulatory metabolic increase. Since, however, core temperature decreases only after metabolic increase has failed to counteract heat loss, and metabolic increase in its turn is preceded by peripheral vasoconstriction, recording of thermal gradients between core and peripheral temperatures has now proven superior in early detection of thermal stress and maintenance of thermal comfort in the neonate. The long-lasting thermal lability of preterm babies partly results from the fact that an elevated basal metabolic rate, which in term neonates compensates for the small body size, is only achieved with delay. As this is correlated to the growth retardation typical of prematurity, the postnatal metabolic increase is usually considered to be a precondition for growth. However, a comparative calorimetric investigation has revealed that in a marsupial species normally born in a very immature state, a rapid weight increase occurs at a low metabolic rate. Obviously, these animals retain a growth efficiency which in humans is confined to intrauterine life and interrupted by preterm birth. Moreover, their low O 2 consumption rate is adaptive to restricted respiratory surface area and incomplete tissue vascularization and contributes to hypoxia tolerance. Therefore, although postnatal metabolic increase promotes thermal stability and weight increase in term and slightly preterm human neonates, metabolic reduction may be the more appropriate strategy in cases where O 2 and substrate supply are limited by extreme immaturity. As long as the factors mediating natural metabolic suppression are unknown, careful thermal protection seems to be one of the most promising ways to prevent uneconomic metabolic activation in highly preterm human neonates.

Labile polycarbonates containing azo units susceptible to thermolytic or acidolytic degradation

Co- and terpolycarbonates containing thermosensitive cycloallylic, benzylic or tertiary diols and, in addition, labile azo functionalities were synthesized in solution from bis(imidazole-carboxylate)s under phase-transfer conditions. The azo groups were introduced by using 2,2'azobis(2-methylpropanol) (1) and azobis(1-hydroxymethyl)cyclohexane (2) as diol components. All copolymers were obtained as amorphous, soft materials with glass transition temperatures below 30°C. Partial crystallinity, however, could be obtained in terpolycarbonates, leading to improved mechanical stability of the products. The polymers were obtained with molar masses Mn in the range 6000-12 900 g/mol. Depending on the structure, the polymers decomposed between 180 and 220°C in a clean, fast, and exothermic process, liberating mostly volatile products. The thermal lability of the azo moieties 1 and 2 was similar to that of the labile carbonate units. In the presence of acids, the thermal stability was drastically reduced and the decomposition started between 65 and 80°C. This allowed the lithographic imaging of these polymers in the presence of a photochemical acid generator. In addition, the imaging of these polymers by UV light in the absence of acid was possible, due to the moderate photolability of the azo group.

Cowpea inhibition of human and bovine protease activities and the effects of processing

The inhibition of human and bovine pancreatic trypsin, chymotrypsin and total proteolytic activity of extracts from the red cowpea was studied. The thermal lability of the inhibitors was also assessed. The raw cowpea samples used had a trypsin inhibitor activity (TIA) level of 14.3 mg trypsin inhibited/g sample. Inhibition of proteolytic activity was influenced by the type and source of pancreatic enzymes. At all levels of raw cowpea extract concentration, bovine trypsin was inhibited to a significantly greater extent ( P < 0.05) than was human trypsin. The most drastic inhibitory effects of raw cowpea was, however, observed in hydrolytic systems containing human chymotrypsin. The action of cowpea inhibitors was less pronounced (maximum of 50% inhibition) on total proteolytic activity compared to individual inhibitions of trypsin and chymotrypsin. With regards to processing effects, almost complete inactivation of inhibitors was achieved by cooking whole cowpea seeds after soaking and dehulling, while only partial inactivation occurred when raw cowpea was milled into flour before cooking. Effective control of the inhibitory activities in cowpea for maximum nutritional benefits can therefore be achieved by soaking, dehulling and cooking whole cowpea seeds.

Electrospray Mass Spectrometric Characterization of Six Therapeutic Oximes: HI-6, HS-6, Obidoxime, 2-PAM, TMB-4 and HLö-7

Pyridinium and bis-pyridinium oxime salts are currently in use or under development for treatment of patients exposed to organophosphorus nerve agents. The low volatility and thermal lability of these compounds limits the number of mass spectrometric approaches that may be used to characterize them. Electrospray mass spectrometry (ESI-MS), a relatively new ionization approach, was investigated as a possible technique for the characterization and identification of these oximes and their degradation products. Six therapeutic oxime salts, the bis-pyridinium oximes, HI-6, HS-6, obidoxime, TMB-4 and HLo-7, and the pyridinium oxime, 2-PAM, were analysed by ESI-MS, making use of collisionally-activated dissociation (CAD) in the ESI interface. The CAD mass spectrum of each oxime was acquired with two different sampling cone voltage settings and the quadrupole mass analyser associated with a hybrid tandem mass spectrometer was utilized for tandem mass spectrometry (MS/MS) and CAD-MS/MS applications including the reliable differentiation of similar bis-pyridinium oximes and the identification of a HI-6 decomposition product.

Isohemagglutinins and xenoreactive antibodies: Members of a distinct family of natural antibodies

Just as anti-blood group A and anti-blood group B antibodies pose a strong humoral barrier to the transplantation of allogeneic organs or blood, xenoreactive natural antibodies directed against Galα1–3Gal pose a barrier to the transplantation of xenogeneic organs or blood. We tested the idea that, although “natural” iso-hemagglutinins and xenoreactive natural antibodies recognize distinct structures, they have a similar origin and function. Anti-A antibodies, anti-B antibodies, and xenoreactive natural antibodies were present in serum at similar concentrations and varied with age, gender, and the concentration of total IgM in serum in a similar manner. Anti-A antibodies, anti-B antibodies, and xenoreactive natural antibodies, unlike some elicited antibodies, had a high degree of thermal lability and bound more avidly at lower temperatures. The natural antibodies manifest remarkable homogeneity and high functional avidity for determinants on a cell surface but only a weak affinity for monovalent ligands. These findings suggest that anti-A antibodies, anti-B antibodies, and xenoreactive natural antibodies specific for Galα1–3Gal have a common origin and function and, given similar antigen density on target cells, provide similar humoral barriers to transplantation or transfusion and that these antibodies may be members of a common “family” of antibodies.

Alkaline Phosphatase Activity in Penicillium roqueforti and in Blue-Veined Cheeses

The Penicillium roqueforti mold exhibits alkaline phosphatase activity. Therefore, blue mold-ripened cheeses made from properly pasteurized milk test positive for phosphatase. Because microbial phosphatases are considered to be more resistant to heat than is milk phosphatase, a statutory control test recommends the repasteurization of cheese at 66°C fir 30min to inactivate selectively the native milk enzyme. However, because of thermal lability of Penicillium roqueforti phosphatase, this control test leads to confusion of the fungal enzyme with native milk alkaline phosphatase and does not confirm whether the milk used to make cheese has been pasteurized.

Stereoselective sulfoxidation of the pesticide methiocarb by flavin-containing monooxygenase and cytochrome P450-dependent monooxygenases of rat liver microsomes. Anticholinesterase activity of the two sulfoxide enantiomers.

Evidence based on thermal lability and enzyme inhibition data suggests that the sulfoxidation of methiocarb (an N-methylcarbamate insecticide) by rat liver microsomes is catalyzed by flavin-containing monooxygenase(s) (FMO) and by cytochrome(s) P450 (P450). In control rats, the relative proportion is ca. 50% P450:50% FMO. Stereoselective formation of methiocarb sulfoxide from the corresponding sulfide has also been examined to compare the enantioselectivity of the two different enzyme systems. Only the FMO-dependent sulfoxidation presents a high stereoselectivity with an enantiomeric excess of 88% in favor of the (A)-enantiomer. Pretreatment of rats with different P450 inducers such as phenobarbital, 3-methylcholanthrene, dexamethasone, and pyrazole did not affect, or decreased, the rate of methiocarb sulfoxidation. Stereoselectivity of the reaction was modified, mainly because of changes in the relative involvement of FMO and P450 in sulfoxidase activity in pretreated animals. The acetylcholinesterase inhibition properties of methiocarb and its main metabolites were also investigated. Racemic methiocarb sulfoxide was slightly less inhibitory (Ki = 0.216 microM-1.min-1) than methiocarb, but a 10-fold difference was observed between the bimolecular rate constants found for the two sulfoxides produced (0.054 and 0.502 microM-1.min-1 for the (A) and (B) enantiomers, respectively).

Mitochondrial NADH [Rightwards Arrow] NAD Transhydrogenation in Adult Hymenolepis diminuta

Adult Hymenolepis diminuta mitochondria catalyze a transhydrogenation reaction between NADPH and NAD and between NADH and NAD. The NADPH-->NAD reaction is catalyzed by an inner membrane-associated pyridine nucleotide transhydrogenase, whereas the NADH-->NAD reaction is ostensibly catalyzed by another system(s). The source(s) of NADH-->NAD activity was evaluated by assessments of its intramitochondrial distribution and thermal lability and by comparisons with the distribution/thermal lability of NADH dehydrogenase, lipoamide dehydrogenase, and NADPH-->NAD transhydrogenase. The occurrence of NADH and lipoamide dehydrogenase components was readily demonstrable. Like NADPH-->NAD transhydrogenase, NADH dehydrogenase was essentially membrane bound. Lipoamide dehydrogenase and NADH-->NAD activities were, at different levels, in the membrane and soluble fractions. Based on thermal profiles, NADH and lipoamide dehydrogenase differed from each other and from NADPH-->NAD transhydrogenase. Although the NADH-->NAD profile closely paralleled that for lipoamide dehydrogenase, it also was similar to the NADH dehydrogenase profile. Collectively, these data are consistent with the supposition that the H. diminuta mitochondrial NADH-->NAD transhydrogenation reaction is catalyzed by lipoamide dehydrogenase and possibly by NADH dehydrogenase rather than by an independent transhydrogenase system.

Drosophila Glutathione S-Transferase D27: Functional Analysis of Two Consecutive Tyrosines near the N-Terminus

The Drosophila glutathione S-transferase D27 (GST D27) has been purified and characterized after direct expression of the intronless gstD27 gene in E. coil. The GST D27 has both conjugation activity against the common substrate 1-chloro-2,4-dinitrobenzene and peroxidase activity against cumene hydroperoxide. Its pH optimum is 8.5 in 0.125 M bis-tris propane buffer at 22°C. It is more thermal labile than the human GST121. The GST D27 has two tyrosines at positions 3 and 4. Both of them appear to be important but neither of them is essential for the enzyme activity. Thus, other residues may also participate in catalysis. The two tyrosines of GST D27 could also be important in binding to GSH or S-hexyl GSH. Results from in vitro biochemical analyses were confirmed by the in vivo activity-based CDNB growth inhibition analyses. Our results clearly indicate that the Drosophila GST D isozymes are different from any of the known mammalian GSTs.

Spectroscopic characterization of some unstable ortho-semiquinone and ortho-quinone complexes of Mn(I) by variable-temperature thin-layer spectroelectrochemistry at optically transparent electrodes

Four carbonyl complexes of Mn I containing 3,5-di-tert.butyl-1,2-semiquinone (DBSQ) and 3,5-di-tert.butyl-1,2-benzoquinone (DBQ) ligands, the radicals [Mn(CO) 3(L)(DBSQ)] and the cationic complexes [Mn(CO) 3(L)(DBQ)] + (L = H 2O, PPh 3), have been characterized for the first time by UV-Vis spectroscopy. These compounds possess limited stability at room temperature with the exception of [Mn(CO) 3(PPh 3)(DBSQ)] which thermally decomposes only in the presence of an excess of PPh 3. The o-(semi quinone complexes under study were electrogenerated inside a recently developed low-temperature optically transparent thin-layer electrochemical (LT OTTLE) cell. The cell is ideally suited for UV-Vis and IR transmission spectroelectrochemical experiments at variable temperatures and allows the study of secondary reactions of the redox products. At T=223 K, the CO disproportionation reaction of the complexes containing the H 2O ligand, decomposition of the tricarbonyl DBQ complexes, and even substitution of the axial CO ligand in [Mn(CO) 3(PPh 3)(DBSQ)] by PPh 3 were fully inhibited. The UV-Vis spectra indicate that the observed thermal lability of the o-quinone complexes [Mn(CO) 4− n (L) n (DBQ)] + ( n=0, 1; L = H 2O, PPh 3 ) most likely originates from a considerably weaker π-acceptor character of the DBQ ligand in these species than imposed in the stable, delocalized complex [Mn(CO) 2(PPh 3) 2(DBQ)] +.

Gold Nanocomposites Prepared by Reactive Sputtering

AbstractReactive sputtering of gold and selected gold alloys in oxygen and nitrogen plasmas generated in a DC glow discharge was studied. Gold alloys examined were various compositions with gallium, aluminum and silicon. Gold is transported unreacted from a gold target to the substrate in a nitrogen plasma to form polycrystalline films, but gold alloys produce fine dispersions of gold in the corresponding ceramic nitride matrix which was crystalline for gallium and amorphous for silicon and aluminum. This contrasts with the behavior in an oxygen plasma which produces pure gold oxide, Au2O3, from a gold target and gold oxide-silicon oxide nanocomposites from Au/Si alloys. Gold oxide is thermally labile and reverts to the elements at 350 °C. Stress in gold oxide films was detected in the decomposition profile, volatile evolution versus temperature, as an event occurring at a lower temperature. The thermal lability of gold oxide was utilized to generate gold nanocomposites in silica with different metal loading through pyrolysis of the corresponding precursor gold oxide-silica films. The properties of gold oxide and gold nanocomposites are described.

Stability of adriamycin-induced DNA adducts and interstrand crosslinks.

The stability of adriamycin-induced DNA adducts and interstrand crosslinks was measured at 37 degrees C by three independent procedures. The loss of [14C]-labelled adducts was described by two first-order decays with half-lives of 7.4 h (60% amplitude) and 39 h (40%). The loss of the drug chromophore also exhibited a biphasic character, with half-lives of 6 h (65%) and approximately 150 h (35%). The decay of transcriptional blockages at an isolated, apparent interstrand GpC crosslinking site was described by two first-order processes, with half-lives of 3 h (65%) and 40 h (35%), whereas the decay of transcriptional blockages at an isolated guanine residue (apparent site of monoadduct) was completely described by a first-order decay with a half-life of 5.3 h. The loss of interstrand crosslinks was measured using a gel electrophoresis assay, and the decay was characterised by a single first-order process with a half-life of 4.7 h. Collectively, these values serve to define a model of the interstrand crosslink with unstable sites of attachment at both ends of the crosslink, with half-lives at either end being approximately 5 and 40 h. The adducts exhibited increasing lability with increasing pH, and were particularly unstable at pH 12, with a half-life of approximately 0.5 h. The adducts were also heat labile, with an overall melting temperature of 67 degrees C (10 min exposure) and this was also the thermal lability measured at three individual adduct sites probed by lambda exonuclease.

Organic geochemistry of freshwater and alkaline lacustrine sediments in the Green River Formation of the Washakie Basin, Wyoming, U.S.A.

Two members of the Green River Formation in the Washakie Basin have been analysed by organic geochemical and organic petrographic techniques and the results placed in a sequence stratigraphic framework. One of these members, the Laney Shale, was deposited in a hydrologically closed, alkaline lake under an arid climate and was characterized by high concentrations of alginite-rich organic matter whereas the other, the Luman Tongue, was deposited in a hydrologically open, freshwater lake under a humid climate and consisted of organic-poor profundal lake mudstones and coaly lake margin sediments. Potential source rocks in both lake types have the potential for generating high-wax oil at high subsurface temperatures (150–175°C at a heating rate of 5 K/Ma) but the alkaline system is clearly more prolific. The most abundant biological marker hydrocarbons were the 4-methylsteranes in both lake types, though dinosteranes were found only in the Laney Shale. Oleanane was absent from the Luman Tongue despite an abundance of angiosperm palynomorphs. Intraformational heterogeneities were best documented for the Laney Shale where molecular differences in kerogen type occur at the parasequence level, with early transgression-, maximum transgression- and rejuvenation stages of lake history having its own kerogen type and distinctive high-wax oil fingerprint. Thermal lability was shown to be linked to kerogen structure, in particular the presence of alicyclic and oxygen-containing moieties, and these in turn are correlated with total organic carbon content and thence productivity/degree of preservation. Some kerogen components appear to have originated via selective preservation whereas others may have been formed by diagenetic condensation reactions.

Escherichia coli expresses a copper- and zinc-containing superoxide dismutase.

A mutant of Escherichia coli, unable to produce manganese- or iron-containing superoxide dismutase (SOD), was found to contain modest levels of an SOD that was judged to be a copper- and zinc-containing SOD on the basis of inhibition by cyanide and inactivation by either H2O2 or diethyldithiocarbamate. Moreover, the diethyldithiocarbamate-inactivated enzyme could be reactivated with Cu(II), and this reconstituted enzyme, like the native enzyme, was unaffected by EDTA and was inhibited by cyanide. This enzyme was, furthermore, selectively released by osmotic shock, in keeping with a periplasmic localization, and it was strongly induced during aerobic growth. This enzyme was also present in the SOD-competent parental strain. Failure to detect it previously can be attributed to its periplasmic localization, thermal lability, sensitivity to pH, and to its relative paucity. It will now be interesting to explore the phenotypic consequences imposed by the absence of this SOD.

Decomposition of Clozapine N-Oxide in the Qualitative and Quantitative Analysis of Clozapine and its Metabolites

Pooled plasma from healthy volunteers was spiked with pure, synthetic clozapine or clozapineN-oxide and then made alkaline with either sodium hydroxide or sodium carbonate. The alkalized samples were allowed to stand at room temperature for various time intervals before extraction with organic solvent and then analyzed by highperformance liquid chromatography. It was found that clozapineN-oxide was reduced to clozapine in plasma made alkaline with sodium hydroxide, but such reduction was negligible in the plasma made alkaline with sodium carbonate. The amount of clozapine produced from clozapineN-oxide depended upon both the strength of the alkali added to the plasma and the duration of exposure of the plasma proteins plus clozapineN-oxide to the alkali. The reduction appears to take place through reducing equivalents generated by the action of strong alkali on plasma proteins. The thermal lability of clozapineN-oxide during gas chromatography–mass spectrometric analysis was also investigated. It was found that clozapineN-oxide was quantitatively decomposed to clozapine during gas chromatography–mass spectrometric analysis.

Thermal degradation products of poly(styrenesulfides) investigated by direct pyrolysis—mass spectrometry and flash pyrolysis—gas chromatography/mass spectrometry

The thermal degradation products of two sulfur polymers, poly(styrenedisulfide) (PSD) and poly(styrenetetrasulfide) (PST), were investigated in parallel by direct pyrolysis—mass spectrometry (DPMS) and by flash pyrolysis-GC/MS (Py—GC/MS). The time-scale of the two pyrolysis techniques is quite different, and therefore they were able to detect significantly different products in the pyrolysis of PSD and PST because of the thermal lability of sulfur-containing compounds. However, the results obtained are not contradictory, and satisfactory mechanisms for the thermal degradation of PSD and PST have been derived from the overall evidence available. Pyrolysis compounds containing sulfur, styrene, and a number of cyclic styrene sulfides and diphenyldithianes have been observed by DPMS. However, in flash pyrolysis-GC/MS, styrene, sulfur, only one cyclic styrene sulfide, and two isomers of diphenylthiophene have been detected. These thiophene derivatives were indeed absent among the compounds obtained by DPMS because they were the terminal (most thermally stable) species arising from further decomposition of the cyclic styrene sulfides formed in the primary thermal degradation processes of PSD and PST.

Axonal regeneration through heat pretreated muscle autografts: An immunohistochemical and electron microscopic study

We have compared the regeneration of axons through frozen-thawed or heated muscle autografts in the sciatic nerve of adult rats. Our results have shown that axons regenerate through muscle grafts which had been either frozen-thawed or heated to 60°C prior to transplantation. However, axons failed to regenerate through muscle grafts which had been pre-heated to 80°C. We speculate that this difference may be related to the thermal lability of components of muscle basal lamina, such as laminin and fibronectin, which are known to play an important role in axonal outgrowth.

Cooperative effects in π-ligand bridged dinuclear complexes: XV. Heterodinuclear FeCo complexes from mononuclear η 5-cyclooctatrienyl iron complexes

The reaction of CpFe(1-5-η-C 8H 8-8- exo-R) (R  CH(CO 2Et) 2: 2a; R  H: 2b) with CpCo(C 2H 4) 2 at T ≤ 40°C yields the diamagnetic heterodinuclear, cyclo-C 8 bridged FeCo complexes [(CpFe)(CpCo)μ-(η 7-C 8H 8R)] (R  CH(CO 2Et) 2: 3; R  H: 4a) which are thermally labile. For 3 the substituent R  CH(CO 2Et) 2 is thermally cleaved with increasing temperature yielding the paramagnetic ESR active 35 valence electron (ve) compound [(CpFe)(CPCo) μ-Cot] ( 5). The ESR data of 5 indicate a cobalt localized unpaired electron. 5 is easily oxidized by O 2, [Ph 3C]BF 4 or [FeCp 2]PF 6 yielding the stable diamagnetic 34 ve cation [(CpFe)(CpCo)μ-Cot] + ( 5 +). Crystal structure analysis of 5BF 4 establishes a synfacial η 5 : η 5 coordination with a very long FeCo distance of about 287(1) pm which is assumed to be too long for a FeCo single bond. The cyclic voltammetry stu 5/ 5 +, 5 +/ 5 2+ and one quasi-reversible redox couple 5 −/ 5. Evidence for the formation of the radical dication 5 2+ containing a Co-centred unpaired electron, can be got from in situ ESR measurements. The thermal lability of 4a leads irreversibly to the isomeric complex 4b at elevated temperature. ' The activation energy Δ E a of this molecular transformation was estimated by 1H NMR spectroscopy as 103 kJ/mol. Preliminary crystal structure determinations of the high temperature isomer 4b confirm a synfacial 1,2,6,7-η:3-5-η bonding mode for the cyclooctatrienyl ligand. The cyclooctatrienyl ligand of the low temperature isomer 4a is assumed to coordinate via a 1-η:6,7-η-bonding mode to the Co centre whereas the coordination mode of the cyclo-C 8 ligand to the Fe centre should occur in 2-5-η fashion. C s molecular symmetry for 4a, which can be deduced from the 1H NMR spectra, is explained by a low energy twitching motion of 4a.

Temperature dependence of growth, enzyme secretion and activity of psychrophilic Antarctic bacteria

Five psychrophilic Antarctic bacteria have been selected for their capacity to secrete exoenzymes into culture medium. These strains are able to grow from 0 to about 25° C. However, production of lipase fromMoraxella, α-amylase fromAlteromonas haloplanctis, β-lactamase fromPsychrobacter immobilis and protease fromBacillus is maximal at temperatures close to that of their environment (—2 to 4° C) and is strongly inhibited at higher temperatures. This thermal effect involves alterations in the secretory pathway in the upper range of temperatures, losses due to the enzyme thermal lability and in some cases to reduction in cell development. The apparent optimal activity temperature of these enzymes is between 30 and 40° C, i.e. about 20° C lower than that of their mesophilic counterparts.