An alternative non-cytochrome containing branch in the respiratory system of free-living Rhizobium phaseoli

The existence of a NADH oxidase catalyzed by a non-cytochrome containing pathway in membranes of free-living Rhizobium phaseoli was explored. This alternative electron transport route was distinguished from the cytochrome-oxidase linked pathway by its low affinity towards O₂ (K , higher K _m for NADH (75 μM), a hundred-fold lower sensitivity to quinarine inhibition, and resistance to UV (360 nm) photoinactivation. In addition to NADH, tetramethyl-p-phenylenediamine (TMPD) donates electrons to this low-O₂ affinity pathway, causing reduction bleaching of a flavoprotein absorption band at 455 nm. Ascorbate-TMPD dependent respiration was partially (25%) inhibited by 200 μM quinacrine. The low O₂-affinity oxidase activity promoted by NADH, or ascorbate plus TMPD was present in aerobic and microaerophilic grown cells and absent in anaerobic and bacteroid cells. Thus, a NADH linked flavoprotein type oxidase is suggested.     

Fermentation parameters of Peptostreptococcus productus on gaseous substrates (CO,H2/CO2)

Intrinsic growth and substrate uptake parameters were obtained for Peptostreptococcus productus, strain U-1, using carbon monoxide as the limiting substrate. A modified Monod model with substrate inhibition was used for modeling. In addition, a product yield of 0.25 mol acetate/mol CO and a cell yield of 0.034 g cells/g CO were obtained. While CO was found to be the primary substrate, P. productus is able to produce acetate from CO₂ and H₂, although this substrate could not sustain growth. Yeast extract was found to also be a growth substrate. A yield of 0.017 g cell/g yeast extract and a product yield of 0.14 g acetate/g yeast extract were obtained. In the presence of acetate, the maximum specific CO uptake rate was increased by 40% compared to the maximum without acetate present. Cell replication was inhibited at acetate concentrations of 30 g/l. Methionine was found to be an essential nutrient for growth and CO uptake by P. productus. A minimum amount of a complex medium such as yeast extract (0.01%) is, however, required.     

Hydrogen peroxide is a product of oxygen consumption byTrichomonas vaginalis

The amitochondriate sexually-transmitted human parasitic protozoanTrichomonas vaginalis (Bushby strain) grown anaerobically on complex medium containing cysteine and ascorbic acid consumed O₂ avidly (6.9 μM min⁻¹ per 10⁶ organisms) with an apparentK _m value of 5.1 μM O₂ : O₂ uptake was inhibited by O₂ > 120 μM. Spectrophotometric assays in the presence of microperoxidase (419-407 nm) indicated that H₂O₂ was produced and that inhibition by high O₂ concentrations was again evident. Hydrogenosomes oxidizing pyruvate in the presence of ADP and succinate showed similar patterns of O₂ consumption, H₂O₂ production (33.5 pmol min⁻¹ per mg protein), and O₂ inhibition. Cytosolic NADH oxidase gave no detectable H₂O₂, whereas the cytosolic NADPH oxidase produced H₂O₂ at a rate (43 pmol min⁻¹ per mg protein) greater than that of hydrogenosomes. These results are discussed in relation to the oxidative stress experienced by the pathogen in its natural habitat.     

Oxygen activation and defence against oxygen toxicity in a psychrophilic bacteroidaceae

When suddenly exposed to air the growth of the obligate anaerobic bacterium of the bacteroidaceae type, strain B6, continues for a few hours before coming to a complete stop. When air is shut off soon after growth has ceased, the organism is able to reestablish anaerobic conditions due to an ability to reduce O₂, and resumes normal growth after another few hours. The O₂ reducing ability of the organism is due to the presence in the cells of a particlebound NADH oxidase, a soluble NADPH oxidase and a soluble pyruvate oxidase. The two pyridine nucleotide oxidase reduce O₂ to H₂O₂, the pyruvate oxidase reduces O₂ to H₂O. Catalase and peroxidase were not detected in anaerobically grown cells. Kinetic studies with cell-free extracts showed that the pyruvate oxidase had a considerably greater affinity (smaller K _m) for O₂ and capacity (higher V _max) for O₂ reduction than the two other oxidases. It is postulated that the pyruvate oxidase acts as a scavenger for O₂, leading to the non-toxic reduction product H₂O, and thus functions as a defense mechanism against oxygen toxicity when the organism is exposed to aerobic condition.Abbreviations PY peptone-yeast extract - PYG PY-glucose - PN pyridine nucleotide - PNH reduced PN - CCCP carbonylcyanide m-chlorophenylhydrazone - DNP 2.4-dinitrophenol     

Purification and characterization of an H<Subscript>2</Subscript>O-forming NADH oxidase from <Emphasis Type="Italic">Clostridium aminovalericum</Emphasis>: existence of an oxygen-detoxifying enzyme in an obligate anaerobic bacteria

Clostridium aminovalericum, an obligate anaerobe, is unable to form colonies on PYD agar plates in the presence of 1% O₂. When grown anaerobically in PYD liquid medium, the strain can continue normal growth after the shift from anoxic (sparged with O₂-free N₂ carrier-gas) to microoxic (sparged with 3% O₂/97% N₂ mixed carrier-gas) growth conditions in the mid exponential phase (OD₆₆₀=1.0). When the strain grew under 3% O₂/97% N₂, the medium remains anoxic. Thirty minutes after beginning aeration with 3% O₂, the activity of NADH oxidase in cell-free extracts increased more than five-fold from the level before aeration. We purified NADH oxidase to determine the characteristics of this enzyme in an obligate anaerobe. The purified NADH oxidase dominated the NADH oxidase activity detected in cell-free extracts. The enzyme is a homotetramer composed of a subunit with a molecular mass of 45 kDa. The enzyme shows a spectrum typical of a flavoprotein, and flavin adenine dinucleotide (FAD) was identified as a cofactor. The final product of NADH oxidation was H₂O, and the estimated K_m for oxygen was 61.9 M. These data demonstrate that an O₂-response enzyme that is capable of detoxifying oxygen to water exists in C. aminovalericum.Abbreviations NRIC NODAI Research Institute-Culture Collection Center, Tokyo University of Agriculture, Tokyo, Japan - SDS-PAGE sodium dodecyl sulfate polyacrylamide gel electrophoresis - PMSF phenylmethylsulfonyl fluoride     

The Structure of an Arabinogalactan Isolated from Bamboo Shoot

It was found that azide bound to alcohol oxidase non-covalently and caused a color change from yellow to red. Alcohol oxidase was purified with a high yield from methanol-limited chemostat-grown cells of Candida boidinii S2 as an enzyme-azide complex by a simple procedure. That is, a cell-free extract was prepared from cells treated with a cationic detergent, Cation M2, and alcohol oxidase amounted to more than 80% of the soluble protein. Inactivation of the enzyme by H₂O₂ and aldehydes was decreased in the complex. The results were discussed as to the production of various aldehydes with the yeast cells.     

Glucocorticoid effects on gastric peroxidase activity

The peroxidase activity in rat gastric mucosa is inhibited after administration of glucocorticoids. The synthetic steroid dexamethasone is more potent than the naturally occurring steroids, such as cortisone or corticosterone. Almost complete inhibition of the enzyme occurs after 24 h with a single dose of 100 μg dexamethasone/120 g body weight. Other mitochondrial enzyme activities, like monoamine oxidase, succinic dehydrogenase and Mg²⁺-ATPase, remain unaltered under the same experimental condition. Submaxillary peroxidase and thyroid peroxidase activity are not inhibited by dexamethasone. Gastric peroxidase activity is increased 200–250% on the 6th day after adrenalectomy. This effect is blocked by the administration of dexamethasone. In fact, the enzyme becomes more sensitive to dexamethasone after adrenalectomy, since it is inhibited by more than 90% at the dose of 25 μg/120 g body weight. The inhibition by dexamethasone in normal animals is reversible. The enzyme is also inhibited after the administration of a single dose of ACTH. The apparent K_m of the enzyme for H₂O₂ is not altered after dexamethasone treatment or after adrenalectomy. The increase in enzyme activity following adrenalectomy is not blocked by actinomycin D or by α-amanitin, but is prevented by puromycin or cycloheximide. After administration of dexamethasone, the iodide concentration process in the gastric mucosa is not affected, but the organification of iodide is significantly diminished.     

Growth of Hansenula polymorpha in a methanol-limited chemostat

Hansenula polymorpha has been grown in a methanol-limited continuous culture at a variety of dilution rates. Cell suspensions of the yeast grown at a dilution rate of 0.16 h^-1 showed a maximal capacity to oxidize excess methanol (QO ₂ ^max ) which was 1.6 times higher than the rate required to sustain the growth rate (Q _O2). When the dilution rate was decreased to 0.03 h^-1, QO ₂ ^max of the cells increased to a value of more than 20 times that of Q _O2. The enzymatic basis for this tremendous overcapacity for the oxidation of excess methanol at low growth rates was found to be the methanol oxidase content of the cells. The level of this enzyme increased from 7% to approximately 20% of the soluble protein when the growth rate was decreased from 0.16 to 0.03 h^-1. These results were explained on the basis of the poor affinity of methanol oxidase for its substrates. Methanol oxidase purified from Hansenula polymorpha showed an apparent K _mfor methanol of 1.3 mM in air saturated reaction mixtures and the apparent K _mof the enzyme for oxygen was 0.4 mM at a methanol concentration of 100 mM.The involvement of an oxygen dependent methanol oxidase in the dissimilation of methanol in Hansenula polymorpha was also reflected in the growth yield of the organism. The maximal yield of the yeast was found to be low (0.38 g cells/g methanol). This was not due to a very high maintenance energy requirement which was estimated to be 17 mg methanol/g cells x h.     

The carbon monoxide- and oxygen-reacting haemoproteins of Streptomyces clavuligerus: cytochrome aa 3 is the predominant terminal oxidase of the respiratory chain

The nature of the carbon monoxide- and oxygen-reacting haemoproteins in the respiratory chain of the filamentous antibiotic-producing bacterium Streptomyces clavuligerus has been investigated. CO-difference (i.e. CO+ reduced minus reduced) spectra of intact cells showed the presence of cytochrome aa ₃, a CO binding b-type cytochrome, and a pigment resembling cytochrome d. In addition, cells that were approaching the end of the growth phase showed the presence of cytochrome P450: this pigment was undetectable in cells harvested early in the growth cycle. High speed centrifugation of cell-free extracts prepared from cells broken by sonication showed that cytochrome aa ₃ was tightly membrane-bound and that cytochrome P450 was soluble. Inhibition of oxygen uptake rates of cells by cyanide indicated that one component, which showed 50% inhibition at 2–4 mM CN^–, was acting as major terminal oxidase: this was observed in cells harvested from all stages of growth. Photodissociation (i. e. photolysed, CO reduced minus CO reduced) spectra at-118°C, in the absence of oxygen, showed cytochrome aa ₃ to be the sole photolysable CO-reacting haemoprotein. At higher temperature (-87°C), in the presence of oxygen, cytochrome aa ₃ formed a complex with oxygen that could not be photolysed by similar intensities of light. By raising the temperature to-43°C, the oxidation of c-type cytochromes was observed. It is concluded that cytochrome aa ₃ is the predominant terminal oxidase in S. clavuligerus and that the other CO reacting haemoproteins, of unknown function, are unlikely to be oxidases.     

High-affinity oxygen uptake byBifidobacterium bifidum

Oxygen uptake by washed cell suspensions ofBifidobacterium bifidum DSM 20082 was studied by using spectrophotometric measurements of the degree of oxygenation of added myoglobin as a measure of the concentration of dissolved O₂. The absorbance changes during consumption of O₂ in a closed reaction vessel were analysed by computer to obtain estimates of the changes in dissolved O₂ concentration. The cell were then used to calculate the rate of O₂ uptake as a function of the dissolved O₂ concentration. The cell suspensions showed Michaelis-Menten kinetics with an apparent K_m value of 0.06 M O₂. Cell-free extracts contained a soluble NADH oxidase activity with a stoichiometry corresponding to the reduction of O₂ to H₂O and with a high affinity for O₂.     

Electron transport chain and energy transduction in Paracoccus denitrificans under autotrophic growth conditions

Cells of Paracoccus denitrificans grown autotrophically with H₂ as energy source contained a branched respiratory chain. The presence of two terminal oxidases was indicated by two cyanide sensitive sites (K _i =10^-5 M and K _i =10^-3 M). While oxidation of NADH and succinate apparently proceeded via both electron pathways as shown by the inhibition of respiration with cyanide and Antimycin A, oxidation of H₂ involved only the terminal oxidase which was less sensitive to KCN. Oxidation of H₂ was not inhibited by rotenone, and sensitive to only relatively high concentrations of Antimycin A (50 nmol/mg).Under our growth conditions, autotrophic cells contained only very small amounts of cytochrome a +a ₃ . A cytochrome b was able to bind CO (with a peak at 418 nm and a trough at 434 nm in the reduced plus CO minus reduced difference spectrum). This cytochrome b had the spectral characteristics of cytochrome o and could be the alternate oxidase. The respiratory chain contained two b cytochromes (b ₅₅₆ and b ₅₆₂ at 77°K); under steady state conditions only b ₅₅₆ was significantly reduced by NADH and succinate while both b ₅₅₆ and b ₅₆₂ were reduced by H₂.Measurement of respiration-driven proton translocation by spheroplasts showed that the oxidation of H₂ by O₂ was associated with a vectorial ejection of H⁺ (in the outward direction) with aH⁺/O value of 6 to 7.A similar result was obtained with succinate. Oxidation of endogenous substrates gave H⁺/O values corresponding to a H⁺/site ratio of 3 with 3 sites functioning in absence of inhibitors, two sites in the presence of rotenone and one site in the presence of antimycin. The H⁺/O values indicated that two energy transducing sites were involved in the oxidation of H₂ by O₂.Measurement of ATP synthesis in membrane vesicles confirmed that phosphorylation was coupled to H₂ oxidation. However, such determinations which necessitated the use of inverted vesicles, gave P/O values too low to allow any conclusions to be made on the number of coupling sites.     

Carbon monoxide sensitivity of cytochrome oxidase in wheat leaves in relation to dwarfing genes (Rht) in wheat cultivars

Summary Leaves of young seedlings of a number of tall cultivars of wheat, lacking the dwarfing Rht genes, readily responded to a brief 2 min exposure to CO, as assessed by in vivo aerobic assay of nitrate reductase. This test depends on the inhibition of cytochrome c oxidase by CO, which in turn renders cytosolic NADH available for the reduction of nitrate to nitrite in vivo. Semi-dwarf cultivars of wheat (Rht present) did not respond to CO in this way. Since CO forms a complex only with reduced cytochrome a₃, the results indicate differences in the redox state of cytochrome a₃, during in situ respiration of leaves from tall and semi-dwarf plants which are likely to be under genetic control.     

Electron transport chain of Saccharomyces cerevisiae mitochondria is inhibited by H2O2 at succinate-cytochrome c oxidoreductase level without lipid peroxidation involvement

The deleterious effects of H₂O₂ on the electron transport chain of yeast mitochondria and on mitochondrial lipid peroxidation were evaluated. Exposure to H₂O₂ resulted in inhibition of the oxygen consumption in the uncoupled and phosphorylating states to 69% and 65%, respectively. The effect of H₂O₂ on the respiratory rate was associated with an inhibition of succinate-ubiquinone and succinate-DCIP oxidoreductase activities. Inhibitory effect of H₂O₂ on respiratory complexes was almost completely recovered by β-mercaptoethanol treatment. H₂O₂ treatment resulted in full resistance to Q_O site inhibitor myxothiazol and thus it is suggested that the quinol oxidase site (Q_O) of complex III is the target for H₂O₂. H₂O₂ did not modify basal levels of lipid peroxidation in yeast mitochondria. However, H₂O₂ addition to rat brain and liver mitochondria induced an increase in lipid peroxidation. These results are discussed in terms of the known physiological differences between mammalian and yeast mitochondria.     

Inhibition of specific electron transport pathways leads to oxidative stress and decreased Candida albicans proliferation

Candida parapsilosis mitochondria contain three respiratory chains: the classical respiratory chain (CRC), a secondary parallel chain (PAR) and an “alternative” oxidative pathway (AOX). We report here the existence of similar pathways in C. albicans. To observe the capacity of each pathway to sustain yeast growth, C. albicans cells were cultured in the presence of inhibitors of these pathways. Antimycin A and KCN totally abrogated yeast growth, while rotenone did not prevent proliferation. Furthermore, rotenone promoted only partial respiratory inhibition. Lower concentrations of KCN that promote partial inhibition of respiration did not inhibit yeast growth, while partial inhibition of respiration with antimycin A did. Similarly, AOX inhibitor BHAM decreased O₂ consumption slightly but completely stunted cell growth. Reactive oxygen species production and oxidized glutathione levels were enhanced in cells treated with antimycin A or BHAM, but not rotenone or KCN. These findings suggest that oxidative stress prevents C. albicans growth.     

Immobilized xanthine oxidase: Kinetics, (in)stability,and stabilization by coimmobilization with superoxide dismutase and catalase

Milk xanthine oxidase was immobilized by covalent attachment to CNBr-activated Sepharose 4B and by adsorption to n-octylamine-substituted Sepharose 4B. The amounts of activity immobilized for the two preparations were 30 and 90%, respectively. The pH optima for free and adsorbed xanthine oxidase were at 8.6 and 8.2, respectively. Both free and immobilized xanthine oxidase show substrate inhibition. The apparent inhibition constant (K_i′) found for adsorbed xanthine oxidase with xanthine as substrate was higher than the K_i for the free enzyme, which was shown to be due to substrate diffusion limitation in the pores of the carrier beads (internal diffusion limitation). Higher substrate concentrations, as desirable for practical application in organic synthesis, can therefore be used with the immobilized enzyme without decreasing the rate. As a result of the internal diffusion limitation the apparent Michaelis constant (K_m′) for adsorbed xanthine oxidase was also higher than the K_m for the free enzyme. Immobilized xanthine oxidase was more stable than the free enzyme during storage at 4 and 30°C. Both forms rapidly lost activity during catalysis. The loss was proportional to the amount of substrate converted. Coimmobilization of xanthine oxidase with superoxide dismutase and catalase improved the operational stability, suggesting that O₂^? and H₂O₂ side-products of the enzymatic reaction were involved in the inactivation. Coimmobilization with albumin also had some stabilizing effect. Complete surrounding of xanthine oxidase by protein, however, by means of etrapment in a glutaraldehyde-crosslinked gelatin matrix, considerably enhanced the operational half-life. This system was less efficient than the Sepharose preparations either because much activity was lost during the immobilization procedure and/or because it had poor flow properties. Xanthine (15 mg)was converted by an adsorbed xanthine oxidase preparation and product (uric acid) was isolated in high yield (84%).     

Correlation of oxygen utilization and hydrogen peroxide accumulation with oxygen induced enzymes in Lactobacillus plantarum cultures

Two strains of Lactobacillus plantarum accumulated H₂O₂ when grown aerobically in a complex glucose based medium. The H₂O₂ accumulation did not occur immediately on exposure of the culture to O₂ but was delayed for a time which, in the case of one strain, was dependent on the amount of inoculum used to seed the culture. The accumulation was always preceded by an increase in the rate of O₂ utilization by the cultures. The latter coincided approximately with an increase in specific activity of NADH oxidase, pyruvate oxidase and NADH peroxidase. H₂O₂ was not a product of NADH oxidase in vitro but was formed in substantial quantities from O₂ during oxidation of pyruvate. The three enzymes were induced by O₂ and H₂O₂; the induction of NADH oxidase responded to lower levels of O₂ (but not of H₂O₂) than the pyruvate oxidase or the NADH peroxidase.Abbreviations MRSG Mann, Rogosa and Sharpe medium (1960) with glucose as fermentation source - TPP thiamin pyrophosphate     

Sporomusa termitida sp. nov., an H2/CO2-utilizing acetogen isolated from termites

H₂-oxidizing CO₂-reducing acetogenic bacteria were isolated from gut contents of Nasutitermes nigriceps termites. Isolates were strictly anaerobic, Gram negative, endospore-forming, straight to slightly curved rods (0.5–0.8×2–8 m) that were motile by means of lateral flagella. Cells were oxidase negative, but catalase positive and possessed a b-type cytochrome(s) associated with the cell membrane. Cells grew anaerobically with H₂+CO₂ as energy source and catalyzed a total synthesis of acetate from this gas mixture. H₂ uptake by a representative isolate (strain JSN-2) displayed a K _m=6 M and V _max=380 nmol x min^-1 x mg protein^-1. Other substrates used as energy sources for growth and acetogenesis included CO, methanol, betaine, trimethoxybenzoate, and various other organic acids. Succinate was also fermented, but propionate was formed from this substrate instead of acetate. Of a variety of sugars and sugar alcohols tested, only mannitol supported growth. Cells grew optimally at 30° C and pH 7.2 and required yeast extract or a source of amino acids (e.g. Casamino acids) for good growth. During initial enrichment and isolation, cells appeared sensitive to various reducing agents commonly employed in media for anaerobes. The DNA base composition of strain JSN-2 was 48.6 mol% G+C. On the bases of cell morphology, substrate utilization spectrum, and DNA base composition, strain JSN-2 is here-with proposed as the type strain of the new species Sporomusa termitida.Journal article no. 12513 from the Michigan Agricultural Experiment Station     

Hydrogen peroxide-induced astaxanthin biosynthesis and catalase activity in Xanthophyllomyces dendrorhous

Xanthophyllomyces dendrorhous (formerly Phaffia rhodozyma) in shake-flask cultures was exposed to 10–20 mmol/L H₂O₂ at various culture stages, and the astaxanthin production was significantly increased by H₂O₂ fed at 0 or 24 h (exponential phase), but only slightly at 48 h (near stationary phase). The astaxanthin production was enhanced most significantly with double feeding of 10 mmol/L H₂O₂ at 0 and 24 h, reaching a cellular content of 1.30 mg/g cell and a volumetric yield of 10.4 mg/L, which were 83 and 65% higher, respectively, than those of the control (0.71 mg/g cell and 6.3 mg/L). The intracellular catalase (CAT) activity was also increased after H₂O₂ treatment. The increases in CAT and astaxanthin of cells could be detected within 4 h of H₂O₂ treatment. The increase in the astaxanthin content of cells was concomitant with a notable decrease in the β-carotene content. The older yeast cells at late culture stage (120 h), due perhaps in part to their higher astaxanthin contents, were more tolerant to H₂O₂ toxicity than the younger cells (24 h). No enhancement of the astaxanthin biosynthesis was attained when H₂O₂ was added to the yeast culture together with a sufficient amount of exogenous CAT. The results suggest that astaxanthin biosynthesis in X. dendrorhous can be stimulated by H₂O₂ as an antioxidative response.     

Microbial oxidases of acidic -amino acids

Two microbial oxidases of acidic -amino acids have been purified to homogeneity. One is a -aspartate oxidase of the yeast Cryptococcus humicolus UJ1 that was induced markedly with -aspartate and is far more active toward -aspartate than -glutamate. The other is a -glutamate oxidase of Candida boidinii 2201 that preferred -glutamate to -aspartate as a substrate in terms of k_cat/K_m, but was not induced very effectively by -glutamate. The most potent competitive inhibitor of the C. humicolus -aspartate oxidase was malonate, and that of the C. boidinii -glutamate oxidase was -malate. The former enzyme was a homotetramer of 160 kDa consisting of subunits of 40 kDa, each of which contained 1 mol of FAD, while the latter was a monomer of 45 kDa. The N-terminal sequences of both enzymes were similar to those of other FAD enzymes and contained a consensus sequence common to most enzymes binding ADP-containing nucleotides. Peroxisomal localization of the C. humicolus -aspartate oxidase was shown by subcellular fractionation and morphological analysis via electron microscopy of C. humicolus cells, where induction of the enzyme was accompanied by induction of catalase and development of peroxisomes. The apo-form of C. humicolus -aspartate oxidase, prepared by removal of FAD was a monomeric protein of 40 kDa, and its binding with FAD proceeded in two stages. The K_d for the apoprotein-FAD complex was very low (8.2×10⁻¹² M) consistent with the observed tight binding. The C. humicolus -aspartate oxidase was essentially similar to other flavoprotein oxidases of acidic and neutral -amino acids with respect to its spectral properties and sensitivity to specific modifying reagents for arginyl and histidyl residues.     

Comparison of some kinetic parameters of peroxidase and IAA oxidase in the course of growth and differentiation of plant cells

An attempt is made to characterize the functional activity of the protein moleculo possessing both peroxidase and IAA oxidase activity by comparing the kinetic parameters for the two types of enzyme activity with regard to the following substrates: H₂O₂, benzidine, guaiacol and IAA. The curves expressing the dependence of the enzyme reaction velocity on the concentration of the enzyme or the substrate are different depending on the enzyme extract origin and the type of the substrate. It is established that the K_m of peroxidase for IAA decreases while its K_m for H₂O₂ increases during cell development. Both types of enzyme activity show similar pH and temperature dependence. The presented data show that IAA oxidase activity of the peroxidase develops as extension and differentiation of the root cells proceed. This is one of the possible mechanisms through which peroxidase may participate in the regulation of growth and differentiation of the primary root cells of maize (Zea mays L.)