Preincubation Temperature Research Articles

Evaluation of the incubated plate count test for pasteurized milk

Factors were examined which may influence bacterial psychrotroph counts obtained by the European Community's directed preincubation test for pasteurized milk. Studies to determine the best protocol for sampling milk indicated that the least counting error was obtained by taking at least five consecutive samples of milk. Increasing the number of replicate plates or making subsamples did not decrease counting error. When milk samples from five commercial dairies were examined over an 11 month period there was a significant difference (p < 0·001) in counts obtained over the period, but this did not seem to be a seasonal effect. The counts between dairies were not significantly different nor was the position in the pasteurization run from which the samples were taken significant. The proportion of samples which failed the test standard was 9.7% over the period. The bacterial flora isolated from plate count agar were identified; Gram­negative rods were the most common isolates. The spiral plater system was compared with the pour plate method in the preincubation test and results were found to be in close agreement, suggesting that the spiral plater could be used to improve the current official methods. Varying the time and temperature of sample preincubation was found to give significantly different results in plate counts. This suggested that preincubation conditons were critical and that variation in conditions even within the specified ranges of the test could significantly alter the bacterial psychrotroph counts obtained. Because of these results, the validity of the statutory test was questioned.

Effect of pre-incubation temperature on the lag time of Aeromonas hydrophila

The effect of prior incubation temperature (5, 15, 25 and 35°C) on the lag times of two strains of Aeromonas hydrophila at the same four incubation temperatures was assessed. When grown at 5°C the type strain (ATCC 7966) showed a 28-fold difference in lag time depending on whether the inoculum had been incubated at 5 or 35°C. However, the corresponding factor for a food-derived strain was only 4. A similar effect was observed, to a lesser extent, under most of the conditions used. Prior incubation temperature had no effect on generation time.

Setting Response of Alaska Pollock Surimi Compared with Beef Myofibrils

ABSTRACTPhysicochemical properties of surimi after preincubation at 25–50°C and beef myofibrils at 25–60°C for up to 8 hr prior to cooking at 80°C for 20 min were evaluated by a torsion test and sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis. Shear stress and true shear strain of surimi were more sensitive to pH changes than beef myofibrils. Maximum gel strength was found at = pH 7 for surimi and pH 6 for beef myofibrils. The myofibrils showed no setting effect at any preincubation temperatures examined, while surimi showed an optimum setting effect at 25°C. Incorporation of beef myofibrils into surimi resulted in decrease of shear stress and true shear strain values.

The effect of environmental conditions on the annual dormancy pattern of seeds of Spergula arvensis

The effect of environmental factors on the germination of exhumed seeds of Spergula arvensis L. after variable periods of burial in soil was investigated. Seeds were buried in the field and exhumed at regular intervals after which germination was tested over a range of conditions. These tests showed clear seasonal changes in dormancy during 3 successive years. Dormancy was broken in spring and reinduced in autumn at rising and falling temperatures, respectively. In experiments in incubators, greater loss of dormancy occurred at 10 and 15 °C than at 2 and 6 °C. As in the field, induction of dormancy occurred when the preincubation temperature was lowered. The expression of the dormancy pattern was strongly influenced by the germination tests conditions. At 15 °C, seeds germinated during a longer period of the year than at 2 or 30 °C. Irradiation with red light, addition of nitrate, and desiccation of the seeds prior to the germination test strongly stimulated germination. All three factors enabled germination of exhumed seeds during a longer period of the year. When light, nitrate, and desiccation were combined, exhumed seeds could germinate in all seasons. The seasonal germination pattern was modelled with a descriptive model based on the dual effect of temperature, which regulates dormancy and also affects germination. This model closely simulated germination at field temperatures. Germination of exhumed seeds in the field was restricted to the period of overlap between the germination temperature range computed with the model and field temperature. The features of the model supported the hypothesis that dormancy of S. arvensis is regulated by the actual changes in temperature rather than the combined effects of a cold and heat sum. Key words: Spergula arvensis, dormancy pattern, germination, regression model, weed seeds.

Chaperonin cpn60 from Escherichia coli protects the mitochondrial enzyme rhodanese against heat inactivation and supports folding at elevated temperatures.

The chaperonin protein cpn60 from Escherichia coli protects the monomeric, mitochondrial enzyme rhodanese (thiosulfate:cyanide sulfurtransferase, EC 2.8.1.1) against heat inactivation. The thermal inactivation of rhodanese was studied for four different states of the enzyme: native, refolded, bound to cpn60 in the form of a binary complex formed from unfolded rhodanese, and a thermally perturbed state. Thermal stabilization is observed in a range of temperatures from 25 to 48 degrees C. Rhodanese that had been inactivated by incubation at 48 degrees C, in the presence of cpn60 can be reactivated at 25 degrees C, upon addition of cpn10, K+, and MgATP. A recovery of about 80% was achieved after 1 h of the addition of those components. Thus, the enzyme is protected against heat inactivation and kept in a reactivable form if inactivation is attempted using the binary complex formed between rhodanese folding intermediate(s) and cpn60. The chaperonin-assisted refolding of urea-denatured rhodanese is dependent on the temperature of the refolding reaction. However, optimal chaperonin assisted refolding of rhodanese observed at 25 degrees C, which is achieved upon addition of cpn10 and ATP to the cpn60-rhodanese complex, is independent of the temperature of preincubation of the complex, that was formed previously at low temperature. The results are in agreement with a model in which the chaperonin cpn60 interacts with partly folded intermediates by forming a binary complex which is stable to elevated temperatures. In addition, it appears that native rhodanese can be thermally perturbed to produce a state different from that achieved by denaturation that can interact with cpn60.

Species-Specific Responses of Membranes and the Na++ K+Pump to Temperature Change in the Kidney of Two Species of Freshwater Fish, Roach (Rutilus rutilus) and Arctic Char (Salvelinus alpinus)

A protocol has been developed for the separation of brush-border membrane (BBM) and basolateral membrane (BLM) fractions from the kidneys of the roach (Rutilus rutilus) and the Arctic char (Salvelinus alpinus), based on differential precipitation and differential centrifugation. Steady state polarization fluorescence was used to measure membrane fluidity in BBM and BLM from the kidneys of cold- and warm-acclimated fish. The homeoviscous response (%HR) in the BLM of cold-acclimated S. alpinus was about four fold higher (78.2%) than in the BLM of cold-acclimated R. rutilus. No %HR was shown by the BBM of R. rutilus, but a fairly strong one (54.3%) by the BBM of S. alpinus. Acclimation temperature had no effect on thermal stabilit, of the (Na⁺ + K⁺)-ATPase from kidney microsomes of S. alpinus, but the preincubation temperature that resulted in 50% inactivation $(LT_{50})$ of the same enzyme was significantly (> 2° C) lower in coldthan in warm-acclimated R. rutilus. No changes or only slight changes of ther...

チリマアジの肉糊のゲル形成と筋原線維タンパク質の変化に見られる特徴

It is already known as “setting phenomena” that the breaking strength of salt-ground meat from walleye pollack, pre-incubated at 30°C or below, increases remarkably when further heated at 90°C.On the other hand, the breaking strengths of salt-ground meat from jurel, preincubated at any given temperature between 20 and 60°C, hardly change upon heating at 90°C. It is also known that the increase in breaking strength of the heated gel from walleye pollack is strongly correlated with the formation of cross-linked myosin heavy chain in it. However, this is not the case in the heated gels through pre-incubation at any temperature of salt-ground meat from jurel. The water drip together with released protein isolated from the heated gel of walleye pollack, formed by preincubation at 30°C or below, is small in quantity, whereas those from the heated gels of jurel, formed at any preincubation temperature, are of relatively large quantity.

Rainbow trout liver activation systems with the ames mutagenicity test

AbstractA poikilothermic metabolic activation system developed from liver homogenate of rainbow trout (Oncorhynchus mykiss, formerly Salmo gairdneri) was used in the Ames Salmonella/Mammalian Microsome Mutagenicity Test. Postmitochondrial fractions (S9) mediated four model promutagens – 2‐aminoanthracene (2AA), 2‐aminofluorene (2AF), benzo[a]pyrene (BaP) and 3‐methylcholanthrene (3MC)–that require two different exogenous metabolic activation routes to form mutagens with Salmonella TA98 and TA100. The enzymatic activity of trout S9 was cytochrome P‐450‐like; it was heat labile and oxygen‐ and cofactor‐dependent. Preincubation temperature significantly influenced the sensitivity of the fish‐activated Ames test. Bacterial mutagenesis with trout activation significantly decreased as preincubation temperature increased; the optimum S9 activation temperature range for trout was 10 to 15°C compared with 37°C for the rat. The liquid‐preincubation test was best adapted to the trout poikilothermic activation system; it was significantly more sensitive than the plate‐incorporation test in detecting histidine revertants. The S9 activity of trout and rat was qualitatively similar in the Ames test: that is, both fractions metabolically activated 2AA, 2AF, BaP and 3MC to produce bacterial mutagenesis with Salmonella TA98 and TA100. The use of this ecologically relevant exogenous activation system in the short‐term predictive genotoxicity testing of freshwater ecosystems is helpful in the assessment of potential hazards of chemical contaminants on fishery resources.

Effects of adhesins from mannose-resistant Escherichia coli on mediator release from human lymphocytes, monocytes, and basophils and from polymorphonuclear granulocytes

We investigated the role of Escherichia coli expressing mannose-resistant hemagglutination and adhesins with regard to the induction of leukotrienes from a suspension of human lymphocytes, monocytes, and basophils (LMBs) compared with human polymorphonuclear granulocytes (PMNs). Genetically cloned E. coli strains expressing various types of mannose-resistant hemagglutination (MRH+) were phagocytosed to a higher degree by monocytes than the nonadherent E. coli strain. The various strains differed in their capacity to induce a chemiluminescence response, which showed the same pattern for LMBs and PMNs. Stimulation of LMBs with bacteria alone, unlike granulocytes, did not activate the cells for the release of leukotrienes. However, preincubation of LMBs with bacteria decreased subsequent leukotriene formation when the cells were stimulated with calcium ionophore. The inhibitory effect was dependent on the concentration of bacteria used for preincubation as well as on the preincubation temperature. The various bacterial strains differed in inhibitory potency for mediator release. Preincubation of LMBs with zymosan, opsonized zymosan, the bacterial peptide FMLP, and peptidoglycan had no inhibitory effect or even increased subsequent leukotriene formation. Opsonized bacteria were far less inhibitory than nonopsonized bacteria. In contrast to human LMBs, preincubation of human PMNs with mannose-resistant bacteria led to increased leukotriene B4 generation and reduced w-oxidation of leukotriene B4. Our data suggest that phagocytes (neutrophils, monocytes) respond in a different way for leukotriene formation after interaction with mannose-resistant E. coli.

Effect of Preincubation Temperature on in Vitro Light Saturated Photosystem I Activity in Thylakoids Isolated from Cold Hardened and Nonhardened Rye

Thylakoids isolated from winter rye (Secale cereale L. cv Muskateer) grown at 5 degrees C or 20 degrees C were compared with respect to their capacity to exhibit an increase in light saturated rates of photosystem I (PSI) electron transport (ascorbate/dichlorophenolindophenol --> methylviologen) after dark preincubation at temperatures between 0 and 60 degrees C. Thylakoids isolated in the presence or absence of Na(+)/Mg(2+) from 20 degrees C grown rye exhibited transient, 40 to 60% increases in light saturated rates of PSI activity at all preincubation temperatures between 5 and 60 degrees C. This increase in PSI activity appeared to occur independently of the electron donor employed. The capacity to exhibit this in vitro induced increase in PSI activity was examined during biogenesis of rye thylakoids under intermittent light conditions at 20 degrees C. Only after exposure to 48 cycles (1 cycle = 118 minutes dark + 2 min light) of intermittent light did rye thylakoids exhibit an increase in light saturated rates of PSI activity even though PSI activity could be detected after 24 cycles. In contrast to thylakoids from 20 degrees C grown rye, thylakoids isolated from 5 degrees C grown rye in the presence of Na(+)/Mg(2+) exhibited no increase in light saturated PSI activity after preincubation at any temperature between 0 and 60 degrees C. This was not due to damage to PSI electron transport in thylakoids isolated from 5 degrees C grown plants since light saturated PSI activity was 60% higher in 5 degrees C thylakoids than 20 degrees C thylakoids prior to in vitro dark preincubation. However, a two-fold increase in light saturated PSI activity of 5 degrees C thylakoids could be observed after dark preincubation only when 5 degrees C thylakoids were initially isolated in the absence of Na(+)/Mg(2+). We suggest that 5 degrees C rye thylakoids, isolated in the presence of these cations, exhibit light saturated PSI electron transport which may be closer to the maximum rate attainable in vitro than 20 degrees C thylakoids and hence cannot be increased further by dark preincubation.

Effect of Varying the Preincubation and Incubation Temperature on the Reaction Pattern for Myosin ATPase in Rat Skeletal Muscle

The temperature of the preincubation and incubation medium influences the staining pattern and intensity of the reverse myofibrillar ATPase in rat skeletal muscle. The activity in some fibers was raised and in others depressed by varying the temperature of the preincubation and incubation medium between 4 and 37 degrees C. This indicates the presence of reverse ATPase isoenzymes with different temperature sensitivities.

In-vitro induction of capacitation of fresh and frozen spermatozoa of the Siberian tiger (Panthera tigris).

Electroejaculates from 5 tigers were split and half of each was assayed fresh while the remainder was frozen and thawed before being assayed. Preincubation time, temperature and removal of seminal plasma were evaluated for their effect on in-vitro capacitation. Ability of spermatozoa to penetrate oocytes, as measured by the zona-free hamster egg-sperm penetration assay (SPA), was used as verification of capacitation. Results of the experiments with fresh semen indicate that: (1) preincubation time affects the fertilizability of tiger spermatozoa with 2 h appearing optimal, (2) a preincubation temperature of 37 degrees C results in significantly higher penetration rates than does a 22 degrees C treatment, and (3) tiger seminal plasma does not appear to contain decapacitation factors, as has been reported for several other species. Frozen semen experiments indicate that (1) frozen-thawed tiger spermatozoa must be removed from the environment of the semen extender before capacitation can take place, and (2) the freeze-thaw procedure results in a shortening of the required capacitation time.

Protection of Pyruvate,Pi Dikinase from Maize against Cold Lability by Compatible Solutes

Most C(4) species are chilling sensitive and certain enzymes like pyruvate,Pi dikinase of the C(4) pathway are also cold labile. The ability of cations and compatible solutes to protect maize (Zea mays) dikinase against cold lability was examined. The enzyme in desalted extracts at pH 8 from preilluminated leaves could be protected against cold lability (at 0 degrees C) by the divalent cations Mn(2+), Mg(2+), and Ca(2+). There was substantial protection by sulfate based salts but little protection by chloride based salts of potassium or ammonium (concentration 250 millimolar). The degree of protection against cold lability under limiting MgCl(2) (5 millimolar) was pH sensitive (maximum protection at pH 8), but independent of ionic strength (up to 250 millimolar by addition of KCl). In catalysis Mg(2+) is required and Mn(2+) could not substitute as a cofactor. Several compatible solutes reduced or prevented the cold inactivation of dikinase (in desalted extracts and the partially purified enzyme), including glycerol, proline, glycinebetaine and trimethylamine-N-oxide (TMAO). TMAO and Mg(2+) had an additive effect in protecting dikinase against cold inactivation. TMAO could largely substitute for the divalent cation and addition of TMAO during cold treatment prevented further inactivation. Cold inactivation was partially reversed by incubation at room temperature; with addition of TMAO reversal was complete. The temperature dependence of inactivation at pH 8 and 3 millimolar MgCl(2) was evaluated by incubation at 2 to 17 degrees C for 45 minutes, followed by assay at room temperature. At preincubation temperatures below 11 degrees C there was a progressive inactivation which could be prevented by TMAO (450 millimolar). The results are discussed relative to possible effects of the solutes on the quaternary structure of this enzyme, which is known to dissociate at low temperatures.

Ligand-specific cross-inhibition of monocyte phagocytosis.

Human monocytes exposed to particles reacting with receptors of one specific type demonstrate a markedly reduced phagocytosis of particles reacting with receptors of another type. The phagocytosis of yeast particles (Saccharomyces cerevisiae) coated with C3 fragments and of uncoated ones by monocytes can inhibit the subsequent endocytosis of sheep erythrocytes sensitized with IgG antibody and vice versa. The erythrocytes were labelled with 51Cr and the yeast particles with 125I. The dependence of the receptor-ligand reaction on temperature and time of preincubation, as well as on ratio of cell and particle, suggests that this cross-inhibition may be associated with plasma membrane modulations beginning with the attachment of ligands to a receptor and followed by their endocytosis. The differences between the functions of temperature, time, and concentration in inhibition caused by different receptor-ligand reactions suggest that these membrane modulations are probably ligand-specific processes.

A hyperthermia study of differential sensitivity and thermotolerance in AKR murine leukemia and normal bone marrow cells

It has been previously demonstrated that AKR leukemia (lymphoma) cells are more sensitive than normal bone marrow cells to hyperthermic killing at 41.8°C and 42.5°C in vitro. This differential heat sensitivity might be explained by a greater ability to induce thermotolerance (TT) in normal versus neoplastic hematopoetic cells. We tested this hypothesis using the spleen colony methodology in the AKR murine model. A greater heat sensitivity of leukemia in comparison to normal bone marrow cells was observed at 42.5°C; this observation agrees with previous reports. However, using a preincubation temperature of 40.0°C for 120 min did not result in the induction of TT in either normal bone marrow (AKR) cells or AKR leukemia cells. The rationale for the choice of preincubation temperatures and times, as well as the clinical implications of these results are discussed.

Synthesis of a novel acetylated neutral lipid related to platelet-activating factor by acyl-CoA:1-O-alkyl-2-acetyl-sn-glycerol acyltransferase in HL-60 cells.

Acyl-CoA:1-O-hexadecyl-2-acetyl-sn-glycerol acyl-transferase, a newly detected enzyme related to platelet-activating factor metabolism, has been characterized in microsomes of a human leukemia cell line (HL-60 cells). It has a sharp pH optimum of 6.8, does not require divalent metal ions, is stable at preincubation temperatures up to 45 degrees C, and among a variety of acyl-CoA thioesters (8:0-20:4) tested, linoleoyl-CoA is the best substrate. Km and Vmax values for 1-O-hexadecyl-2-acetyl-sn-glycerol acyltransferase are 8.5 microM and 1.7 nmol/min/mg of protein, respectively. For comparative purposes acyl-CoA:1,2-dioleoyl-sn-glycerol acyltransferase was also characterized in HL-60 microsomes. It has a relatively broad pH optimum of 6.1, is stimulated 1.4-fold by Mg2+, is relatively labile at preincubation temperatures higher than 25 degrees C, and among the various acyl-CoA thioesters tested, myristoyl-CoA is the best substrate. In substrate competition experiments, we found 1-O-hexadecyl-2-oleoyl-sn-glycerol is a competitive inhibitor (Ki = 32 microM). Our findings indicate acyl-CoA:1-O-hexadecyl-2-acetyl-sn-glycerol acyltransferase in HL-60 cells is distinctly different from acyl-CoA:1,2-dioleoyl-sn-glycerol acyltransferase. Our experimental results demonstrate that the unique enzyme activity characterized in this report also is expressed in intact HL-60 cells.

Lethal exposure times and preconditioning to upper temperature limits of some temperate North Atlantic red algae

Using the red algaPolyneura hilliae as an example, the minimum time taken for lethal temperature exposure, with no regeneration capacity left, was 2 weeks. Employing this exposure time, the upper temperature limits of the following 13 red algal species belonging to four biogeographical distribution groups were determined:Callophyllis lacinita, Polyneura hilliae, Hypoglossum hypoglossoides, Halurus equisetifolius, Lomentaria articulata, Cryptopleura ramosa, Calliblepharis ciliata (warm-temperate Mediterranean-Atlantic group);Callithamnion tetragonum, Lomentaria orcadensis (amphiatlantic-temperate group);Grinnellia americana, Lomentaria baileyana, Agardhiella subulata (northeast American tropical-temperate group),Solieria tenera (amphiatlantic tropical-temperature group). Pre-incubation temperatures of 10 and 20°C for one month (or 15 and 25°C for the two last-mentioned distribution groups) did not measurably affect the critical survival temperature.

Membrane fluidity regulates development of gonadotrope desensitization to GnRH

Development of GnRH-mediated gonadotrope desensitization was examined under conditions in which membrane fluidity was altered by temperature and/or chemical means. Cultured pituitary cells were preincubated at temperatures ranging from 4°C to 37°C for 3 h with a desensitizing concentration of GnRH (10 −9 M) or with vehicle alone. Cells were then rinsed and responsiveness assessed by a second 3 h incubation with GnRH at 37°C. As preincubation temperatures decreased from 37°C to 23°C, development of desensitization in gonadotropes was progressively reduced. At 23°C and below, gonadotropes failed to become desensitized to GnRH. Decreases in membrane fluidity occurred over the same temperature range as measured directly by fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene incorporated into plasma membrane. When membrane fluidity was increased by incubating cells with the membrane mobilizing agent 2-(2-methoxy-ethoxy)-ethyl-8-( cis-2- n-octylcyclopropyl)-octanoate (A 2C), low temperature blockade of GnRH-mediated gonadotrope desensitization was reversed. A 2C had no measurable effects on either GnRH receptor binding or number and caused no cytotoxic effects. These studies suggest that development of gonadotropine desensitization to GnRH can be regulated by the state of membrane fluidity.

Are Ca 2+-dependent proteases really responsible for Cl −-dependent and Ca 2+-stimulated binding of [ 3H]glutamate in rat brain?

The role of Ca 2+ ions in [ 3H]glutamate binding was re-examined using synaptic membranous preparations obtained from the rat brain. In vitro addition (0.1–5 mM) of calcium chloride exhibited a profound enhancement of the binding in a temperature-dependent manner, whereas that of calcium acetate had no significant effect on the binding independently of the incubation temperature. Calcium acetate elicited a significantly additional stimulation of the Cl −-induced and temperature-dependent facilitation of the binding. The augmentation by these two ions was invariably eliminated by the addition of an antagonist for the anion channels including picrotoxin as well as of inhibitors of anion transport such as ethacrynic acid and 4,4′-diisothiocyanatostilbene-2,2′-disulfonic acid. l-Aspartate exerted a more potent inhibitory action on the Cl −-dependent binding and Cl −-dependent and Ca 2+-stimulated binding, than d-asparate. The latter two bindings were selectively abolished by an agonist (quisqualic acid) and an antagonist ( dl-2-amino-4-phosphonobutyric acid) for central glutamate receptors, respectively. It was also found that pretreatment of the membranes with calcium acetate resulted in a complete abolishment of the Ca 2+-stimulated binding with a concomitant stimulation of the Cl −-dependent binding, which invariably occured independently of the preincubation temperature (2 or 30 °C). No significant alteration was detected in the basal binding following the latter pretreatment. None of various protease inhibitors such as leupeptin, antipain, chymostatin and pepstatin induced a significant alteration in the basal, Cl −-dependent, Ca 2+-stimulated and Na +-dependent bindings of [ 3H]glutamate, respectively. These results suggest that Ca 2+ ions may elicit their stimulatory action on the Cl −-dependent binding of [ 3H]glutamate even in the absence of Cl − ions added through the temperature-independent and apparently irreversible interaction with the anion transport carriers rather than the direct action on the binding sites of the ligand. The evidence presented here also suggests that the widely held view that Ca 2+-dependent proteases are responsible for the exbition of Cl −-dependent and Ca 2+-stimulated binding of [ 3H]glutamate may need to be re-evaluated.

Evidence for changes in the conformational status of rat liver microsomal glucose-6-phosphate:phosphohydrolase during detergent-dependent membrane modification. Effect of p-mercuribenzoate and organomercurial agarose gel on glucose-6-phosphatase of native and detergent-modified microsomes.

Comparative studies investigating influences of temperature and time of preincubation on the interactions of an organomercurial agarose gel and p-mercuribenzoate with glucose-6-phosphatase of native and Triton X-114-modified rat liver microsomes were carried out. The effect of p-mercuribenzoate on glucose 6-phosphate hydrolysis is a result of two processes, a moderate membrane perturbation connected with release of some latency and temperature- and time-dependent inhibition of the catalytic activity. Short-term preincubation with both organic mercurials at 37 degrees C is a necessary condition for the entire inhibition of the enzyme activity of native as well as of Triton X-114-modified microsomes. A binding site of the phosphohydrolase itself is accessible to p-mercuribenzoate and the phenyl mercury residue of the affinity gel from the cytoplasmic surface even in native microsomes. Kinetic analyses reveal a formally competitive mechanism of inhibition using native microsomes, but the kinetic picture changes to a noncompetitive pattern of Lineweaver-Burk plots when the inhibitor-loaded microsomes are modified optimally by Triton X-114. This behavior can be evaluated as the first convincing evidence for drastic changes of the conformational status of the phosphohydrolase during the membrane modification process. A combined conformational flexibility-substrate transport model characterizing the microsomal glucose-6-phosphatase as an integral channel-protein embedded within the hydrophobic interior of the membrane is proposed.