粘虫飞行过程中四种相关酶的活性变化

对3日龄粘虫雌蛾吊飞过程中4种相关酶3-羟酰辅酶A脱氢酶(HOAD)、3-磷酸甘油醛脱氢酶(GAPDH)、3-磷酸甘油脱氢酶(GDH)和乳酸脱氢酶(LDH)的研究结果表明,在室内条件下,粘虫在吊飞过程中其能量代谢有以下特点： 在吊飞的初始5 min,所有与糖代谢和脂肪代谢相关的酶活性都快速升高,这段时期脂肪代谢的酶活性也完全被活化,HOAD活性明显增强;但在随后的5～60 min持续吊飞期间与能量代谢有关的酶活性都有所下降,表明此时飞行活性趋于平稳。飞行中的粘虫具有极高的有氧代谢能力,也具备一定的无氧代谢能力。吊飞过程中HOAD∶GAPDH大于1,说明粘虫飞行过程中能源物质利用属于混合型,但动用脂肪比糖类要多。     

Xenobiotica-metabolizing enzymes in Drosophila melanogaster: activities of epoxide hydratase and glutathione S-transferase compared with similar activities in rat liver.

Activities of epoxide hydratase and glutathione (GSH) S-transferase were investigated in subcellular fractions of Drosophila melanogaster, and these activities were compared with analogous enzymic activities in extracts from rat liver. Microsomes of Drosophila were active in the hydratation of styrene oxide catalyzed by epoxide hydratase. The post-microsomal supernatant of Drosophila catalyzed the conjugation of GSH with 1-chloro-2,4-dinitrobenzene. However, GSH S-transferase activity with styrene oxide as the electrophilic substrate was not measurable. The respective specific activities of epoxide hydratase (per mg microsomal protein) and GSH S-transferase (per mg cytosolic protein) were factors of 5- and 10-fold lower than the corresponding activities in rat liver. However, when expressed per gram body weight, activities of both epoxide hydratase and GSH S-transferase were 3 times higher for Drosophila enzymes. The apparent Km values for the two Drosophila enzymes were higher, whereas the apparent Km values were lower, than the values found for the rat-liver enzymes. Among 3 different Drosophila strains (a wild-type, a white eye-color carrying mutant strain and a DDT-resistant strain), preliminary experiments showed no differences as far as these two enzymic activities were concerned. It is concluded that the results obtained in genetic toxicology testing with Drosophila are probably relevant to effects to be expected in mammalian systems with compounds requiring metabolic processes involving the enzymes investigated here.     

Effects of maternal thiamine deficiency on the development of thiamine-dependent enzymes in regions of the rat brain

Previous studies suggest that developing rat brain is susceptible to reduced thiamine intake. In order to assess the metabolic basis for this susceptibility, activities of three thiamine-dependent enzymes (pyruvate dehydrogenase complex, -ketoglutarate dehydrogenase and transketolase) were measured in homogenates of brain tissue from the offspring of thiamine-deficient mothers. Control groups of animals were pair-fed to equal food consumption with the thiamine-deficient animals. The study revealed region-selective delays in the establishment of adult activities of thiamine-dependent enzymes as a result of maternal thiamine deficiency. Pyruvate dehydrogenase complex activities in cerebral cortex were significantly reduced (by 20% P < 0.05); -ketoglutarate dehydrogenase activities were also reduced in cerebral cortex (by 30% P < 0.05). In the case of transketolase, enzyme activities were significantly reduced in cerebral cortex, cerebellum and brainstem. Following thiamine replenishment, defective enzyme activities were restored to normal in all cases. However, since thiamine-dependent enzymes are important for the establishment of adult patterns of cerebral energy metabolism and also in myelin synthesis, maternal thiamine deficiency resulting in reductions of thiamine-dependent enzymes at a vulnerable period in brain development could have serious metabolic consequences leading to permanent neurological sequellae in the offspring.     

Effects of prolactin and androgens on enzymes of carbohydrate metabolism in prostate of castrated bonnet monkeys Macaca radiata (Geoffroy).

Effects of prolactin (PRL), bromocriptine (Br), testosterone propionate (TP), dihydrotestosterone (DHT) and the combinations of these androgens with PRL/Br on the specific activities of caudal and cranial prostatic cellular enzymes involved in carbohydrate metabolism in castrated mature bonnet monkeys have been studied. Castration decreased all the enzymes studied such as hexokinase (HK), 6-phosphofructokinase (6-PFK), glyceraldehyde-3-phosphate dehydrogenase (G-3-PD), pyruvate kinase (PK), glucose-6-phosphate dehydrogenase (G-6-PD) and 6-phosphogluconate dehydrogenase (6-PGD) in the cranial and caudal prostates. PRL elevated the activities of all the enzymes above normal except G-3-PD of cranial lobe. In the caudal lobe, PRL brought back the activities of HK, PFK, PK, G-6-PD to normal and 6-PGD above normal except G-3-PD. TP/DHT treatment increased all the enzymes in both the lobes. PRL given along with TP/DHT further enhanced the androgen action with regard to HK, PK, G-6-PD and 6-PGD of cranial and PFK, G-3-PD, PK, G-6-PD and 6-PGD of caudal lobe. Br treatment did not produce any alteration of these enzymes in both the lobes. In the cranial lobe, during Br+TP/DHT treatment, the stimulating effects of androgen were unaffected on all the enzymes except PK. On the other hand in the caudal, the stimulatory effects of androgens were affected and the activities of HK, PFK, PK and 6-PGD were significantly decreased. The present results suggest that PRL has a direct as well as a synergistic action with androgens on enzymes of EMP and HMP shunt in the prostates of monkeys.     

The pentose phosphate pathway of glucose metabolism. Hormonal and dietary control of the oxidative and non-oxidative reactions and related enzymes of the cycle in adipose tissue

1. Measurements were made of the activities of the enzymes of the pentose phosphate pathway concerned in both the oxidative (glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase) and the non-oxidative (ribose 5-phosphate isomerase, ribulose 5-phosphate epimerase, transketolase and transaldolase) reactions of this pathway, together with hexokinase and phosphoglucose isomerase, in adipose tissue in a variety of nutritional and hormonal conditions. 2. Starvation for 2 days caused a significant decrease in the activities of all the enzymes of the pentose phosphate pathway, with the exception of glucose 6-phosphate dehydrogenase, when expressed as activity/2 fat-pads; only the activities of ribose 5-phosphate isomerase and ribulose 5-phosphate epimerase were significantly decreased on the basis of activity/mg. of protein. Re-feeding with a high-carbohydrate or high-fat diet for 3 days restored the activity of all the enzymes of the pentose phosphate pathway to the range of the control values, with the exception of transketolase, which showed a marked ;overshoot' in rats re-fed with carbohydrate. Starvation for 3 days caused a marked decrease in the activities of glucose 6-phosphate dehydrogenase and transketolase. 3. On the basis of activity/two fat-pads, alloxan-diabetes caused a marked decrease, to about half the control value, in the activities of all the enzymes concerned in the pentose phosphate pathway, transketolase showing the smallest decrease; hexokinase and phosphoglucose isomerase activities were also decreased. Treatment with insulin for 3 and 7 days raised the activities to normal or supranormal values, transketolase showing the most marked ;overshoot' effect. On the basis of activity/mg. of protein the activity of none of the enzymes was significantly decreased in alloxan-diabetes; transketolase and transaldolase activities were raised above the control values. With insulin treatment for 3 or 7 days the activities of all the enzymes were significantly increased, except that of ribulose 5-phosphate epimerase at the shorter time-interval. Glucagon treatment did not alter any of the enzyme activities expressed on either basis. 4. Thyroidectomy caused a decrease of 30-40% in the activities of enzymes of the pentose phosphate pathway, except for transketolase activity, which fell to 50% of the control value. Little change occurred in adipose-tissue weight or protein content. 5. Adrenalectomy caused a decrease of 40% in the activity of glucose 6-phosphate dehydrogenase and of 20-30% in the activities of the remaining enzymes of the pentose phosphate pathway; hexokinase activity was also decreased. Treatment with cortisone for 3 days did not significantly raise the activity from that found in adrenalectomized rats. Treatment of normal rats with high doses of cortisone had no significant effect on the activities of the enzymes of the pentose phosphate pathway in adipose tissue. 6. The changes in enzyme activities are discussed in relation to: (a) the concept of constant-proportion groups of enzymes; (b) the known changes in the flux of glucose through alternative metabolic pathways; (c) the pattern of change found in liver with similar hormonal and dietary conditions.     

Urea cycle disorder in C3H-H-2 degree mice with juvenile steatosis of viscera

We determined the activities of urea cycle enzymes in the liver of C3H-H-2 degree-jsv mice. The activities of all urea cycle enzymes decreased in the latter period of lactation. The activities of carbamylphosphate synthetase and ornithine transcarbamylase in some affected mice were undetectable. On the other hand, the activities of enzymes other than urea cycle enzymes were normal. We consider that the decrease in the urea cycle enzymes is caused by an abnormality in the mechanism of gene expression.     

Longterm stability of phase I and phase II enzymes of porcine liver cells in flat membrane bioreactors

Recently, researchers have focused on the use of bioartificial liver devices to support patients with fulminant hepatic failure. Our team developed a cell-based flat membrane bioreactor (FMB). In this, porcine liver cells were maintained in 3D-coculture between two gel layers in a sandwich configuration for 3 weeks to study the influence of this bioreactor technique on the preservation of basic, not induced activities of phase I and phase II enzymes. First, the time and substrate dependencies of the following enzymes were measured: ethoxyresorufin-O-deethylase (EROD, CYP 1A1/1A2) and ethoxycoumarin-O-deethylase (ECOD, CYP 2B6) as phase I enzymes, and glutathione-S-transferase (GST), UDP-glucuronosyltransferase (UGT) and sulfotransferase (ST) as phase II enzymes. To find optimal test conditions Michaelis-Menten kinetics were calculated. Next, different potential inducers were tested to find out the most effective compounds. Based on these results, the basic, not induced levels of the different enzymes were determined in the flat membrane bioreactor. Furthermore, the response of these enzyme activities to the chosen inducers was investigated to examine whether the cells keep their ability for drug-drug interactions. Basic, not induced activities of both phase I enzymes and the phase II enzymes GST and UGT were maintained at nearly the initial levels during the complete period of study. In addition, it was possible to induce these enzymes twice or three times in a weekly interval. In contrast, the basic, not induced activity of ST increased during the first 10 days of culture. It stabilized then and was maintained steady. As in short-term investigations, no reaction of the ST-activity towards any inducer could be obtained. These results prove that porcine liver cells preserve their phase I and phase II activities and respond to inducing drugs over 3 weeks in culture. Therefore, the flat membrane bioreactor is not only suitable for investigating drug metabolism, drug-drug interactions, and enzyme induction but also for supporting liver functions.     

Further serum related alterations in the activities of some membrane marker enzymes in normal and virus transformed cells

The activities of membrane marker enzymes in normal (3T3) and simian virus transformed mouse cells (SV3T3) are affected not only by densities of cultures but also by the sera types used in the growth media. We have assayed the levels of 5'nucleotidase, monoamine oxidase and rotenone insensitive NADH ferricyanide reductase in these cells grown to sparse and confluent cultures in medium supplemented with 10% newborn calf serum (n.c.s.) or in medium supplemented with 10% foetal bovine serum (f.b.s.). It was found that in 3T3 cells grown in 10% f.b.s. the transition from sparse to confluent cultures was associated with a reduction in the activities of the marker enzymes while in those grown in 10% n.c.s., the activities of these enzymes increased. In the SV3T3 cells, the activities of all the enzymes except for monoamine oxidase decreased from sparse to confluent culture densities in cells grown in 10% n.c.s. whereas in those grown in 10% f.b.s. there were no significant change in the activities of the enzymes over the same culture densities. The results suggest that the marker enzymes are affected by sera types and culture densities.     

Enzymes of glucose metabolism in Frankia sp.

Enzymes of glucose metabolism were assayed in crude cell extracts of Frankia strains HFPArI3 and HFPCcI2 as well as in isolated vesicle clusters from Alnus rubra root nodules. Activities of the Embden-Meyerhof-Parnas pathway enzymes glucokinase, phosphofructokinase, and pyruvate kinase were found in Frankia strain HFPArI3 and glucokinase and pyruvate kinase were found in Frankia strain HFPCcI2 and in the vesicle clusters. An NADP+-linked glucose 6-phosphate dehydrogenase and an NAD-linked 6-phosphogluconate dehydrogenase were found in all of the extracts, although the role of these enzymes is unclear. No NADP+-linked 6-phosphogluconate dehydrogenase was found. Both dehydrogenases were inhibited by adenosine 5-triphosphate, and the apparent Km's for glucose 6-phosphate and 6-phosphogluconate were 6.86 X 10(-4) and 7.0 X 10(-5) M, respectively. In addition to the enzymes mentioned above, an NADP+-linked malic enzyme was detected in the pure cultures but not in the vesicle clusters. In contrast, however, the vesicle clusters had activity of an NAD-linked malic enzyme. The possibility that this enzyme resulted from contamination from plant mitochondria trapped in the vesicle clusters could not be discounted. None of the extracts showed activities of the Entner-Doudoroff enzymes or the gluconate metabolism enzymes gluconate dehydrogenase or gluconokinase. Propionate- versus trehalose-grown cultures of strain HFPArI3 showed similar activities of most enzymes except malic enzyme, which was higher in the cultures grown on the organic acid. Nitrogen-fixing cultures of strain HFPArI3 showed higher specific activities of glucose 6-phosphate and 6-phosphogluconate dehydrogenases and phosphofructokinase than ammonia-grown cultures.     

低致死剂量氯虫苯甲酰胺对沟金针虫食物利用和相关生理生化指标的剂量和时间效应

【目的】明确氯虫苯甲酰胺对沟金针虫Pleonomus canaliculatus亚致死效应的生理生化机制,阐明氯虫苯甲酰胺低致死剂量对沟金针虫食物利用、能量物质含量以及体内消化酶、保护酶和解毒酶活力的影响。【方法】室内采用土壤混药法测定氯虫苯甲酰胺对沟金针虫3龄幼虫毒力,并测定了氯虫苯甲酰胺LC₁₀, LC₂₅和LC₄₀低致死剂量对沟金针虫3龄幼虫营养指标和体内能量物质含量的影响;采用酶动力学法检测了氯虫苯甲酰胺低致死剂量处理1, 6, 12, 24, 48和72 h后沟金针虫3龄幼虫体内消化酶(蛋白酶、α-淀粉酶、脂肪酶、海藻糖酶)、保护酶(CAT, POD和SOD)以及解毒酶(CarE, MFO和GST)活力的动态变化。【结果】氯虫苯甲酰胺对沟金针虫3龄幼虫有较高毒力,其LC₅₀值为1.2397 mg/kg。LC₁₀和LC₄₀剂量氯虫苯甲酰胺处理沟金针虫3龄幼虫后,平均相对生长率(MRGR)和近似消化率(AD)显著降低,严重干扰其对食物的利用;LC₁₀, LC₂₅和LC₄₀剂量处理后沟金针虫3龄幼虫体内主要的能量物质(蛋白质、脂质、碳水化合物、海藻糖)含量和消化酶活力均明显降低,而解毒酶和保护酶活力显著增加,最终延缓其生长发育。【结论】氯虫苯甲酰胺对沟金针虫幼虫具有很高的杀虫活性,低致死剂量氯虫苯甲酰胺处理沟金针虫幼虫后,通过抑制消化酶活性,使其对食物的利用能力降低和生长发育延缓,以及诱导解毒酶和保护酶活性来阻止外界毒物侵害。研究结果为阐明氯虫苯甲酰胺对沟金针虫的亚致死效应机制及作用机理提供了一定的理论基础。     

东北虎幼体消化系统蛋白水解酶的初步研究

蛋白水解酶在许多生命活动中是必需的物质(Vassalli and Pepper,1994)。蛋白质的酶解修饰(Xuet al.,1999)、细胞迁移、组织再生与修复、消化系统对蛋白质的消化等均与蛋白水解酶有关(Baimbridgeet al.,1992),且蛋白水解酶功能失调会导致许多疾病(Teichertet al.,1989)。东北虎(     

Induction of drug metabolizing enzymes in the liver of diabetic mice

The effects of two classical inducers, phenobarbital and 3-methylcholanthrene, have been tested on some liver microsomal drug-metabolizing enzymes (monooxygenases and phase II enzymes) and on benzo(a)pyrene metabolism in genetically (ob/ob) and chemically (streptozotocin) diabetic mice. 1) In ob/ob mice, the basal activities and the inducibility of phase I and phase II enzymes, as well as the electrophoretic pattern of microsomal proteins, were not notably different from those of similarly treated lean mice. 2) A possibly common form of cytochrome P 450 present both in microsomes from steptozotocin-diabetic non-induced mice and in those from phenobarbital-treated non-diabetic mice could explain the increased "phenobarbital-like" enzyme activities in chemically diabetic animals. 3) The increase of monooxygenase activities produced by streptozotocin treatment is partially depressed by 3-methylcholanthrene, probably as a result of the dilution of "phenobarbital-like" cytochrome P 450 forms by 3-methylcholanthrene-induced cytochrome P 448. 4) The increased formation of the most carcinogenic metabolites of benzo(a)pyrene, and the slight decrease of phase II conjugation enzyme activities, may add their deleterious effects in 3-methylcholanthrene-induced streptozotocin-diabetic animals.     

Nitrogen metabolism-related enzymes in <Emphasis Type="Italic">Mesembryanthemum crystallinum</Emphasis> after <Emphasis Type="Italic">Botrytis cinerea</Emphasis> infection

We compared C₃ and CAM (crassulacean acid metabolism) states in Mesembryanthemum crystallinum, a facultative CAM species, with respect to the involvement of phosphoenolpyruvate carboxylase (PEPC) and nitrogen metabolismrelated enzymes in plant response to Botrytis cinerea infection. The enzyme activities were monitored both in pathogeninoculated 2^nd leaf pair and non-inoculated 3^rd leaf pair. The control activities of most studied enzymes were dependent on the mode of photosynthesis. Compared to C₃ plants, those performing CAM exhibited higher PEPC, nitrate reductase (NR), and deaminating glutamate dehydrogenase (NAD-GDH) activities but lower glutamine synthetase (GS) and alanine aminotransferase (ALT) activities. Regardless of the mode of photosynthetic carbon assimilation, the plants responded to infection with enhancement of PEPC and inhibition of NR activities in the inoculated leaves. Whereas the activity of GS remained unaffected, those of all glutamate-yielding enzymes, namely ferredoxin-dependent glutamate synthase (Fd-GOGAT), aspartate aminotransferase (AST), ALT, and aminating glutamate dehydrogenase (NADHGDH) were altered after infection. However, the time-course and extent of the observed changes differed in C₃ and CAM plants. In general, CAM plants responded to infection with an earlier increase in PEPC and Fd-GOGAT activities as well as later inhibition of NR activity. Contrary to C₃ plants, in those performing CAM the activities of PEPC, Fd-GOGAT, NADH-GDH, and AST in the non-inoculated 3^rd leaf pair were similarly influenced by infection as in leaves directly inoculated with the pathogen. This implies that the local infection induced an alteration of carbon/nitrogen status in healthy upper leaves. This reprogramming resulting from changes in PEPC and nitrogen metabolism-related enzymes was C₃- and CAM-specific.     

Development of Endopeptidase Activities in Maize (Zea mays L.) Endosperms

An activity stain was used after native polyacrylamide gel electrophoresis, and at least 17 different endopeptidase activities were detected in maize (Zea mays L.) endosperm extracts prepared during the first 6 d after imbibition. The enzymes detected were classified into four groups based on their time of appearance and on their mobility in polyacrylamide gels. The first group, which included two enzymes present in dry endosperms, disappeared soon after imbibition. The second group, comprising five activity bands, appeared during the first 2 to 3 d after imbibition and then disappeared. The third set of enzymes increased continuously throughout the experimental period. The fourth group appeared after d 3 and remained at a constant level after that time. The endopeptidase activities were characterized by the effect of specific inhibitors on their activities. The two enzymes of the first group are metalloendopeptidases based on their sensitivity to ethylenediaminetetracetate (EDTA). Enzymes of the second, third, and fourth groups are sulfhydryl-endopeptidases as judged by their sensitivity to antipain, chymostatin, leupeptin, and E-64 and by their requirement for 2-mercaptoethanol. Pepstatin, phenylmethylsulfonyl fluoride, or EDTA had no effect on these enzymes. Many of the second, third, and fourth group enzymes cleaved [alpha]-zein-rich proteins as well as such easily obtained proteins as gelatin (used in our standard assay) and hemoglobin. The second group had a high affinity for [gamma]-zein, whereas none of the bands in the fourth group of enzymes cleaved this type of zein. The two metalloenzymes of the first group cleaved neither [alpha]- nor [gamma]-zeins.     

Steady-state enzyme kinetics of the pancreatic ribonucleases from five mannalian species.

The kinetic parameters Km, k+2 and k+2/Km of the pancreatic ribonucleases (EC 3.1.4.22) from cow, giraffe, horse, rat and lesser rorqual have been determined, using 2',3'-cyclic cytidine monophosphate and 2',3'-cuclic uridine monophosphate as substrates. No large differences were found between the activities of the five enzymes. The relative differences between the activities of the five enzymes are mainly due to differences in the rates of hydrolysis and not to differences in the affinities for the substrates.     

Lymphatic transport of cellular enzymes from muscle into the intravascular compartment.

In an experimental study, employing anaesthetized dogs, it was investigated whether cellular enzymes from peripheral skeletal muscle get into the circulating blood by diffusion across capillary membranes or by lymphatic transport. In the experimental group 1, the animals were anaesthetized only. The plasma activities of the four enzymes measured--lactate dehydrogenase, aspartate aminotransferase, alanine aminotransferase, creatine kinase--did not show any mentionable change during a time period of 6 h. In group 2 one hind limb of each animal was moved passively for 1 h. Alanine aminotransferase remained unchanged in plasma, the activities of the three other enzymes increased significantly. In group 3 one hind limb was made hypoxic by clamping the femoral blood vessels for 1 h. No activity changes were observed. When the period of hypoxia was followed by a 1-hour period of passive movement in group 4, the alterations in plasma activities were almost identical to those observed in group 2. In group 5 the experimental procedure was as in group 4, in addition the lymph from the thoracic duct was quantitatively withdrawn. The enzyme activities in plasma revealed a tendency to decrease rather than increase. Lymph flow increased significantly as well as the lymphatic activities of those enzymes which have high intracellular activities in muscle. The results prove, that enzymes from muscle are transported from the interstitial into the intravascular compartment mainly by lymphatic transport. Indications were found that the interruption of blood flow in one hind limb did not result in an enzyme release from muscle cells. It is discussed how changes in lymph flow, occurring during physical exercise for example, affect enzyme activities in plasma.     

Periodate-oxidized AMP as a substrate, an inhibitor and an affinity label of human placental alkaline phosphatase.

1. Addition of glucose induced an inactivation of mitochondrial enzymes in the yeast Saccharomyces cerevisiae containing normal mitochondrial particles. 2. The glucose-induced inactivation of mitochondrial enzymes was inhibited by the presence of cycloheximide. 3. Pepstatin also inhibited the inactivation, but phenylmethanesulphonyl fluoride accelerated the inactivation. 4. The specific activities of fructose 1,6-bisphosphatase and cytoplasmic malate dehydrogenase were decreased on the exposure to glucose, as well as those of the mitochondrial enzymes. However, the glucose-induced inactivation of cytoplasmic enzymes was not inhibited by the presence of pepstatin. 5. The specific activities of hexokinase and phosphofructokinase, which are cytoplasmic enzymes were increased by the addition of glucose, and this effect was not affected by pepstatin. 6. Addition of glucose resulted in an increase in the synthesis of proteins of the mitochondria and the cytosol, and simultaneously in degradation of these mitochondrial and cytoplasmic proteins.     

Enzymology of the beta-ketoadipate pathway in Trichosporon cutaneum.

Cell extracts were prepared from Trichosporon cutaneum grown with phenol or p-cresol, and activities were assayed for enzymes catalyzing conversion of these two carbon sources into 3-ketoadipate (beta-ketoadipate) and 3-keto-4-methyladipate, respectively. When activities of each enzyme were expressed as a ratio, the rate for methyl-substituted substrate being divided by that for the unsubstituted substrate, it was apparent that p-cresol-grown cells elaborated pairs of enzymes for hydroxylation, dioxygenation, and delactonization. One enzyme of each pair was more active against its methyl-substituted substrate, and the other was more active against its unsubstituted substrate. Column chromatography was used to separate two hydroxylase activities and also 1,2-dioxygenase activities; the catechol 1,2-dioxygenases were further purified to electrophoretic homogeneity. Extracts of phenol-grown cells contained only those enzymes in this group that were more active against unsubstituted substrates. In contrast, whether cells were grown with phenol or p-cresol, only one muconate cycloisomerase (lactonizing enzyme) was elaborated which was more active against 3-methyl-cis,cis-muconate than against cis,cis-muconate; in this respect it differed from a cycloisomerase of another strain of T. cutaneum which has been characterized. The cycloisomerase was purified from both phenol-grown and p-cresol-grown cells, and some characteristics were determined.