ACCUMULATION OF 4-O-β-D-GLUCOSIDE OF PROTOCATECHUIC ACID IN THE LEFT COLLETERIAL GLAND OF THE COCKROACH, PERIPLANETA AMERICANA. II. HORMONAL REGULATION

The amount of protocatechuic acid glucoside in the left colleterial gland changes with the reproductive cycle. Allatectomy, beheading and injection of actinomycin D cause inhibition of the accumulation of glucoside, but glucoside resumes to accumulate in the left colleterial gland with the reimplantation of corpora allata into the allatectomized cockroaches.
When ¹⁴C-glucose was injected in normal animals, radioactive glucoside was accumulated in the left colleterial gland whereas in the allatectomized cockroaches, it was not accumulated in the gland but was found abundantly in blood.
The level of protocatechuic acid glucoside synthetase activity of the fat body tissue and of the left colleterial gland was assayed. The enzyme activity in the left colleterial gland was not affected by allatectomy but that in the fat body was slightly affected.
The mechanism of accumulation of protocatechuic acid glucoside in the left colleterial gland and the endocrine control on the accumulation are discussed.     

The conversion of 3-deoxyarabinoheptulosonate 7-phosphate to 3-dehydroquinate by sorghum seedling preparations

Partially purified preparations from etiolated sorghum seedlings catalyzed the conversion of DAHP to DHQ. The reaction catalysed by DHQ synthetase was stimulated by 0.1 μM to 0.1 mM NAD in the presence O-0.5 mM Co²⁺. NADH at 1 μM stimulated the reaction as much as 50% but became inhibitory at 100μM. Co²⁺ at 0.5mM stimulated enzyme activity 3-fold; Mg²⁺, Mn²⁺, Cu²⁺, and Zn²⁺ were not stimulatory. EDTA at 5 mM inhibited the reaction 95% but its effects were reversed by equal concentrations of Co²⁺. Phe, Tyr, Trp, t-cinnamate, several hydroxylated cinnamates, DHS, quinate, and shikimate at 0.3 mM failed to affect enzyme activity but slight inhibition occurred with DHQ and protocatechuic acid at 0.3 mM, inhibition being 14 % and 22 %, respectively. DHQ synthetase activity also was detected in spinach leaves and potato tuber tissue. Synthetase activity appeared to increase in response to injury of potato tuber and sweet potato root tissues.     

Purification of fat body glutathione S‐transferase from the desert locust Schistocerca gregaria: investigation of flavonoid inhibitory effects on enzyme activity

Focus on the development of botanical insecticides such as polyphenols may represent an alternative method to chemical control. In the present study, total glutathione concentration and its related antioxidant enzymes in foregut, midgut, hindgut and fat body homogenates of the desert locust Schistocerca gregaria are examined. Glutathione S‐transferase (GST) activity exhibits a significantly higher value in fat bodies compared with other tissues. A simple and reproducible procedure for the purification of S. gregaria fat body GST is established and the purified enzyme is shown to be homogenous. The purified GST displays a typical Michaelis behaviour with respect to its substrates. Characterization of the GST, including optimum pH, substrate specificity and inhibitor effects, is carried out. The ability of some flavonoids to inhibit S. gregaria fat body GST activity is examined. High‐performance liquid chromatography analysis indicates that the major components in Glycyrrhiza glabra roots are 18α‐glycyrrhetinic acid, quercetin and rutin, and the major components in Hibiscus sabdariffa calyx are cyanidin 3‐O‐glucoside chloride and delphinidin. Quercetin and delphinidin chloride exhibit strong GST inhibition and the inhibition type is determined for both. Rutin shows a smaller inhibitory effect, whereas 18α‐glycyrrhetinic acid and cyanidin have no effect. Inhibition of S. gregaria fat body GST activity would be expected to prevent, or at least delay, the development of resistance to chemical pesticides. Among the examined levels of the antioxidant enzymes, total glutathione concentration and its related enzymes in foregut, midgut, hindgut and fat body crude homogenates of S. gregaria GST activity exhibit a significantly higher value in fat bodies compared with other tissues. Some flavonoids that are detected in H. sabdariffa calyx and G. glabra root extracts are the most effective inhibitors of the purified S. gregaria fat body GST activity. Inhibition of S. gregaria fat body GST activity by quercetin and delphinidin (major compounds detected by HPLC) would be expected to prevent, or at least delay, the development of resistance to chemical pesticides.     

Evidence for the presence of mandelic acid dehydrogenase and benzoyl formate decarboxylase in the american cockroach

Incubation of benzoyl formate with crude body homogenates of the American cockroach produces a significant release of CO₂ above control values. Partial purification of the enzyme by gel filtration removes endogenous substrate but the enzymatic activity is still present.Labelled ¹⁴C-carboxy-mandelic acid incubated with NAD⁺ liberates ¹⁴CO₂ under similar conditions, which suggests that mandelic acid may be converted to benzoyl formate prior to decarboxylation.The rôle of the enzymes in the possible conversion of tyrosine to protocatechuic acid, an oöthecal tanning agent, is discussed.     

Metabolism of juvenile hormone in cultures of ovaries and fat body in the cockroachperiplaneta Americana

Summary The time course of juvenile hormone (JH) metabolism is examined in cultures ofPeriplaneta americana fat body and ovaries in medium containingManduca sexta carrier protein or cockroach hemolymph. In the absence ofM. sexta carrier protein or cockroach hemolymph, both tissues extensively catabolize exogenous [³H]JH in the medium. Addition of the carrier protein or hemolymph to the culture system prevents the hydrolysis of the hormone in the medium. Within the tissues JH is degraded whether or not carrier protein or hemolymph is present which suggests that the protective role of these molecules is exclusively extracellular. Incubation of [³H]JH with medium preconditioned with tissue results in destruction of the hormone. This suggests that the fat body secretes esterases into the medium. In contrast, the ovarioles hydrolyze the hormone by means of cell-associated enzyme. The relationship of these phenomena to insect development is discussed. This work supported by NSF Grant PCM 76-02229 and University of Kansas Biomedical Sciences Grant RR-07037.     

Identification and characterization of uncoupling protein 4 in fat body and muscle mitochondria from the cockroach <Emphasis Type="Italic">Gromphadorhina cocquereliana</Emphasis>

We have identified and characterized an uncoupling protein in mitochondria isolated from leg muscle and from fat body, an insect analogue tissue of mammalian liver and adipose tissue, of the cockroach Gromphadorhina coquereliana (GcUCP). This is the first functional characterization of UCP activity in isolated insect mitochondria. Bioenergetic studies clearly indicate UCP function in both insect tissues. In resting (non-phosphorylating) mitochondria, cockroach GcUCP activity was stimulated by the addition of micromolar concentrations of palmitic acid and inhibited by the purine nucleotide GTP. Moreover, in phosphorylating mitochondria, GcUCP activity was able to divert energy from oxidative phosphorylation. Functional studies indicate a higher activity of GcUCP-mediated uncoupling in cockroach muscle mitochondria compared to fat body mitochondria. GcUCP activation by palmitic acid resulted in a decrease in superoxide anion production, suggesting that protection against mitochondrial oxidative stress may be a physiological role of UCPs in insects. GcUCP protein was immunodetected using antibodies raised against human UCP4 as a single band of around 36 kDa. GcUCP protein expression in cockroach muscle mitochondria was significantly higher compared to mitochondria isolated from fat body. LC-MS/MS analyses revealed 100% sequence identities for peptides obtained from GcUCP to UCP4 isoforms from D. melanogaster (the highest homology), human, rat or other insect mitochondria. Therefore, it can be proposed that cockroach GcUCP corresponds to the UCP4 isoforms of other animals.     

Biosynthesis of thromboxanes in human platelets. I. Characterization and assay of thromboxane systhetase

An enzyme system which catalyzes the rapid conversion of prostaglandin endoperoxide to thromboxane B₂ was found in the microsomal fraction of human platelet homogenate. The products of the reaction were identified by gas chromatography-mass spectrometry as thromboxane B₂ and the C-17 hydroxy fatty acid HHT. A simple radiometric TLC method was developed for the determination of the enzyme activity. Various parameters affecting the enzyme activity have been defined. Thromboxane synthetase was strongly inhibited by its substrate analogs. The activity was completely abolished when low amounts (5 × 10^?5$\text{M}$) of the 9,11 (epoxymethano) prostanoic acid was included in the assay mixture. The enzyme reaction was not affected by nonsteroidal antiinflammatory agents.     

THE ROLE OF GLUTAMINE SYNTHETASE IN THE INCORPORATION OF AMMONIUM IN SKELETONEMA COSTATUM (BACILLARIOPHYCEAE)1

The K_m for ammonia for glutamine synthetase and glutamate dehydrogenase was measured in enzyme extracts from Skeletonema costatum (Grev.) Cleve. At similar physiological pH and temperature the half-saturation constant for glutamine synthetase was 29 μM, whereas for GDH it was 28mM. On the basis of relative enzymic activity, as well as substrate affinity, it is suggested that glutamine synthetase is the enzyme primarily responsible for the incorporation of ammonium into the amino acid pool, when extracellular nitrogen is at ecological concentrations.     

THE RELATION BETWEEN BIOCHEMICAL AND MORPHOLOGICAL DIFFERENTIATION IN BLASTOCLADIELLA EMERSONII. I. ENZYMATIC SYNTHESIS OF GLUCOSAMINE-6-PHOSPHATE

Lovett , James S., and Edward C. Cantino . (Michigan State U., East Lansing.) The relation between biochemical and morphological differentiation in Blastocladiella emersonii. I. Enzymatic synthesis of glucosamine-6-phosphate. Amer. Jour. Bot. 47(6): 499–505. Illus. 1960.—The enzyme glucosamine synthetase (glutamine-fructose-6-phosphate transamidase) was purified ca. 19-fold from extracts of the aquatic phycomycete, Blastocladiella emersonii, by centrifugation, protamine sulfate fractionation, and adsorption on Ca₃(PO₄)₂ gel The pH optimum, time course, and relation between enzyme concentration and reaction rate were established for the partially purified synthetase. The reaction was the same as that of the enzyme of Neurospora crassa: D-fructose-6- phosphate + L-glutamine —> D-glucosamine-6-phosphate + L-glutamic acid. The 20-fold purification attained resulted in an enzyme preparation with a specific activity 40 times greater than that reported for other organisms to date.     

Cloning of PaAtg8 and roles of autophagy in adaptation to starvation with respect to the fat body and midgut of the Americana cockroach,Periplaneta americana

Starvation, in particular amino acid deprivation, induces autophagy in trophocytes (adipocytes), the major component of the fat body cell types, in the larvae of Drosophila melanogaster. However, the fat body of cockroach has two additional cell types: urocytes depositing uric acid in urate vacuoles as a nitrogen resource and mycetocytes harboring an endosymbiont, Blattabacterium cuenoti, which can synthesize amino acids from the metabolites of the stored uric acid. These cells might complement the roles of autophagy in recycling amino acids in the fat body or other organs of cockroaches under starvation. We investigate the presence of autophagy in tissues such as the fat body and midgut of the American cockroach, Periplaneta americana, under starvation by immunoblotting with antibody against Atg8, a ubiquitin-like protein required for the formation of autophagosomes and by electron microscopy. Corresponding changes in acid phosphatase activity were also investigated as representing lysosome activity. Starvation increased the level of an autophagic marker, Atg8-II, in both the tissues, extensively stimulating the formation of autophagic compartments in trophocytes of the fat body and columnar cells of the midgut for over 2 weeks. Acid phosphatase showed no significant increase in the fat body of the starved cockroaches but was higher in the midgut of the continuously fed animals. Thus, a distinct autophagic mechanism operates in these tissues under starvation of 2 weeks and longer. The late induction of autophagy implies exhaustion of the stored uric acid in the fat body. High activity of acid phosphatase in the midgut of the fed cockroaches might represent enhanced assimilation and not an autophagy-related function.     

Quinate:NAP(P)+-oxidoreductase from Larix sibirica: purification,characterization and function

Quinate:NAP(P)⁺-oxidoreductase (QORase, EC 1.1.1.24), which catalyzes the interconversion of quinic and 3-dehydroquinic acids, was purified from the needles and developing xylem cells of Larix sibirica. The enzymes from these two tissues were partially characterized and compared. QORase from needles had optimum pH at 9.0 and apparent K_m values of 1.84 mM for quinic acid and 0.19 mM for NADP⁺. The enzyme was activated by phosphoenolpyruvate. Gallic and protocatechuic acids were formed in a reaction mixture of purified enzyme from needles as final products of quinic acid transformation. QORase from developing xylem cells showed pH optimum at 10.0 and had apparent Km values of 0.70 mM for quinic acid and 0.05 mM for NADP⁺. The enzyme was not affected by PEP. The divalent cations Co²⁺ and Mn²⁺ at least doubled activity of QORase from both sources but Mg²⁺ affected the enzyme from needles only. The spatial organization and regulation of quinic acid metabolism in the autotrophic and heterotrophic cells of conifers and the role of QORase in this process are discussed.     

Acylation of steryl glucosides by phospholipids. Solubilization and properties of the acyl transferase.

Particulate enzyme preparations of cotton fibers catalyze the acylation of exogenous steryl glucoside to form acylated steryl glucoside. The acyl transferase involved in this reaction was solubilized by treatment of the membrane fractions with Triton X-100 and was partially purified by chromatography on DEAE-cellulose and gel filtration. This solubilized enzyme had an absolute requirement for Triton X-100 and phospholipid in order to catalyze the acylation of the steryl glucoside. The best phospholipid substrate was phosphatidylethanolamine but egg and soybean phosphatidylcholine were also active. The phospholipid was shown to function as an acyl donor by demonstrating that [¹⁴C]fatty acid from ¹⁴C-labeled phospholipid could be transferred to steryl-[³H]glucoside to form [¹⁴C,³H]acylated steryl glucoside. Saponification of this compound yielded [¹⁴C]fatty acid and steryl-[⁷H]glucoside.     

The Pimelyl-CoA Synthetase Responsible for the First Step in Biotin Biosynthesis by Microorganisms

Cell-free extracts of various bacteria were active in catalyzing the synthesis of pimelyl-CoA from pimelic acid and CoA. The pimelyl-CoA formed was determined in a reaction coupled with the 7-keto-8-aminopelargonic acid (KAPA) synthetase system, which is required to convert pimely-CoA to KAPA, and by microbiologically assaying the amount of KAPA formed. The enzyme synthesizing pimelyl-CoA was named pimely-CoA synthetase and should belong to EC 6.2.1. The pimelyl-CoA synthetase reaction required pimelic acid, CoA, ATP and Mg²⁺. The enzyme was partially purified from a cell-free extract of Bacillus megaterium. Using purified enzyme, characterization of the enzyme was performed. The enzyme reaction was remarkably inhibited by typical metal-chelating agents. Mn²⁺ and ADP could replace Mg²⁺ and ATP, respectively. No feedback repression was observed even with the addition of 1.0 µg per ml of biotin to the culture medium.     

Fractionation and characterization of cellular membranes from root tips of garden cress (Lepidium sativum L.)

The first step in the gravitropic reaction chain, i.e. perception, is known to occur in the statenchyma of the root cap. Because of the importance of the root tip in graviperception, a procedure has been developed to isolate root tips from garden cress (Lepidium sativum L.). The root tip fraction contains the tissues of the root cap plus the lower half of the meristem zone, but is clearly separated from the tissues of the elongation zone, the zone of gravitropic response. Membranes from the root tip and root base fractions have been centrifuged on sucrose density gradients and the marker enzyme profiles analyzed. These results show that the marker enzyme profiles for vacuoles, dictyosomes, mitochondria, and plasma membranes are similar in the root tip or root base fractions. The endoplasmic reticulum (ER) has a shoulder of cytochrome c reductase activity at a density of 1.16 g cm^-3 which is distinct from the other enzyme activities and is only observed in root tip preparations. The specific enzyme activity for ER, cytochrome c reductase, was enriched in root tip membranes 1.7 fold. This latter increase is interpreted as at least in part an increased ER content in the root tip.Abbreviations ASG 6-acyl-steryl glucoside - ER endoplasmic reticulum - IDP inosine-5-diphosphate - INT 2-(4-iodophenyl)-3-(4-nitrophenyl)-5-phenyltetrazolium chloride - PM plasma membrane - SG steryl glucoside     

Fat body is the site of vitellogenin synthesis in the soft tick,Ornithodoros moubata

Summary Vitellogenin (Vg) synthesis in cultured tissues was analysed biochemically in a soft tick,Ornithodoros moubata. Nine tissue fractions dissected from reproductive females were incubated in vitro in a specially designed Ringer containing³⁵S-methionine. The synthesis of total protein and Vg was assayed by the radioactivity incorporated into precipitates with trichloroacetic acid and antivitellin (Vn)-serum, respectively. Fat body was the most active tissue in Vg synthesis, which comprised 46% of the Vg synthesis by all tissues and 42% of total protein synthesis by fat body. Protein synthesized by the fat body and precipitated with anti-Vn-serum was shown by electrophoresis and fluorography, to consist of six radioactive polypeptides corresponding to the components of Vg. Vg synthesized in cultured fat body was first accumulated in the tissue and secreted into the medium during incubation. Some tissues other than fat body showed low Vg synthesis (in each, less than 12% of total protein synthesis) which, however, may be due to contamination by fat body cells as seen with the scanning electron microscope (SEM). SEM also showed that fat body cells in the active stage of Vg synthesis expanded about 10-fold in length. Immunohistochemical analysis showed a very strong reaction with anti-Vn-IgG in the cytoplasm of fat body from reproductive females. Fat body from unfed females and other tissues including midgut, did not show any specific fluorescence. A positive reaction was obtained with developing oocytes. These results indicate that the fat body is the only site of Vg synthesis in this tick.Abbreviations Vg vitellogenin - Vn vitellin - SDS sodium dodecyl sulfate - PAGE polyacrylamide gel electrophoresis - SEM scanning electron microscopy - TCA trichloroacetic acid     

Identification of Predominant Phytochemical Compounds and Cytotoxic Activity of Wild Olive Leaves (Olea europaea L. ssp. sylvestris) Harvested in South Portugal

This study has been aimed at providing a qualitative and quantitative evaluation of selected phytochemicals such as phenolic acids, flavonoids, oleuropein, fatty acids profile, and volatile oil compounds, present in wild olive leaves harvested in Portugal, as well as at determining their antioxidant and cytotoxic potential against human melanoma HTB‐140 and WM793, prostate cancer DU‐145 and PC‐3, hepatocellular carcinoma Hep G2 cell lines, as well as normal human skin fibroblasts BJ and prostate epithelial cells PNT2. Gallic, protocatechuic, p‐hydroxybenzoic, vanillic acids, apigenin 7‐O‐glucoside, luteolin 7‐O‐glucoside, and rutin were identified in olive leaves. The amount of oleuropein was equal to 22.64 g/kg dry weight. (E)‐Anethole (32.35%), fenchone (11.89%), and (Z)‐3‐nonen‐1‐ol (8%) were found to be the main constituents of the oil volatile fraction, whereas palmitic, oleic, and alpha‐linolenic acid were determined to be dominating fatty acids. Olive leaves methanol extract was observed to exerted a significant, selective cytotoxic effect on DU‐145 and PC‐3 cell lines. Except the essential oil composition, evaluated wild olive leaves, with regard to their quantitative and qualitative composition, do not substantially differ from the leaves of other cultivars grown for industrial purposes and they reveal considerable antioxidant and cytotoxic properties. Thus, the wild species may prove to be suitable for use in traditional medicine as cancer chemoprevention.     

Ascorbate peroxidase: A novel antioxidant enzyme in insects

Ascorbate peroxidase (APOX) activity, which catalyzes the oxidation of ascorbic acid with the concurrent reduction of hydrogen peroxide (H₂O₂), was found in larvae of Helicoverpa zea. Since insects apparently lack a Se-dependent glutathione peroxidase and since catalase has a low affinity for H₂O₂, this enzyme may be important in removing H₂O₂ in insects. We partially purified the APOX activity 58x from the whole body homogenates and investigated its activity with model lipid peroxides, electron donors, and known inhibitors of plant APOX. The H. zea APOX has activity with model lipid peroxides. This, along with the APOX activity found in fat body tissues, suggests that ascorbate peroxidase may be important in removing lipid peroxides in insects. The H. zea APOX has broader specificity for electron donors than the plant APOX with activity using cysteine, NADPH, glutathione, and cytochrome C as electron donors (22–93% of activity with ascorbate). The H. zea APOX is also resistant to many of the known inhibitors of plant APOX, suggesting that the enzyme has a different active site and may not be a heme-peroxidase. © 1997 Wiley-Liss, Inc.     

Chicken liver fatty acid synthetase: Proteolysis by subtilisin and isolation and properties of palmitoyl thioesterase

Subtilisin hydrolysis of chicken liver fatty acid syntheiase yields polypeptides of molecular weights 220,000, 160,000 and 35,000. The larger peptides are further degraded to proteins of molecular weights 122,000 and 105,000. When 50% and 80% of the synthetase subunits are cleaved, there is a loss of 10% and 40% of fatty acid synthetase activity, respectively, indicating that proteolysis of the 240,000-mol. wt. subunit does not substantially affect palmitate synthesis provided that the component polypeptides remain associated with each other. Ammonium sulfate fractionation yields a fraction containing the palmitoyl thioesterase activity. Polyacrylamide gel electrophoresis of this fraction under both nondenaturing and denaturing conditions yields one band with an estimated molecular weight of 35,000. The isolated thioesterase is specific for palmitoyl and stearoyl thioesters (myristoyl-CoA is hydrolyzed at 15% the rate of palmitoyl-CoA). The enzyme is inhibited byN-ethylmaleimide and diisopropylfluorophosphate, suggesting that both an active -SH and -OH are involved in catalysis. However, preincubation of the thioesterase with decanoly-CoA protected the enzyme against inhibition by diisopropylfluorophosphate but not byN-ethylmaleimide, suggesting that an active OH (seryl or threonyl) is involved in the hydrolysis of the palmitoyl group. This active hydroxyl group is uniquely inhibited by diisopropylfluorophosphate, as evidenced by the incorporation of 2 mol of [³²P]diisopropylfluorophosphate per mole of synthetase (M _r = 480,000) and the fact that all the radioactivity was associated with the isolated thioesterase. These results indicate that there are two copies of the thioesterase per mole of synthetase or one copy of the enzyme per 240,000-mol. wt. subunit.     

New Developments in Selenium Biochemistry: Selenocysteine Biosynthesis in Eukaryotes and Archaea

We used comparative genomics and experimental analyses to show that (1) eukaryotes and archaea, which possess the selenocysteine (Sec) protein insertion machinery contain an enzyme, O-phosphoseryl-transfer RNA (tRNA)^[Ser]Sec kinase (designated PSTK), which phosphorylates seryl-tRNA^[Ser]Sec to form O-phosphoseryl-tRNA^[Ser]Sec and (2) the Sec synthase (SecS) in mammals is a pyridoxal phosphate-containing protein previously described as the soluble liver antigen (SLA). SecS uses the product of PSTK, O-phosphoseryl-tRNA^[Ser]Sec, and selenophosphate as substrates to generate selenocysteyl-tRNA^[Ser]Sec. Sec could be synthesized on tRNA^[Ser]Sec from selenide, adenosine triphosphate (ATP), and serine using tRNA^[Ser]Sec, seryl-tRNA synthetase, PSTK, selenophosphate synthetase, and SecS. The enzyme that synthesizes monoselenophosphate is a previously identified selenoprotein, selenophosphate synthetase 2 (SPS2), whereas the previously identified mammalian selenophosphate synthetase 1 did not serve this function. Monoselenophosphate also served directly in the reaction replacing ATP, selenide, and SPS2, demonstrating that this compound was the active selenium donor. Conservation of the overall pathway of Sec biosynthesis suggests that this pathway is also active in other eukaryotes and archaea that contain selenoproteins. X.-M. Xu and B. A. Carlson contributed equally to the studies described herein.     

Metabolism of Indole-3-acetaldehyde. III. Some Characteristics of the Aldehyde Oxidase of Avena Coleoptiles

Coleoptiles of Avena contain a soluble enzyme system, capable of oxidizing indoleacetaldehyde (lAAld) to indoleacetic acid (IAA). There is a gradient in the concentration of the enzyme along the length of the coleoptile and the first inter-node. The top 5 mm segment of each organ is relatively richer in this enzyme than the rest of the tissue. The enzyme was purified 17.7-fold by fractional precipitation with ammonium sulphate followed by gel filtration on Sephadex. Optimal pH for lAAld oxidation is ca. 4.4. Activity of the enzyme is normally oxygen obligatory. But, in the absence of oxygen, phenazine methosulphate (PMS) serves as hydrogen acceptor for aldehyde oxidation, but not some other dyes tried. Approximately one mole of oxygen was consumed for each mole of IAA formed. Formation of H₂O₂ could not be detected. Added H₂O₂ inhibited the reaction. Prolonged dialysis progressively inactivated the enzyme. Added NAD, NADP, FMN, FAD, cytochrome c, cyanoco-balamin, folic acid and ascorbic acid did not restore the lost activity. But 10^?3M cysteine restored about 60 % of the lost activity. The enzyme is an acidic protein, isoelectric at pH 4.05. For lAAld, under the conditions of experimentation, a Km of 3.45 × 10^?4M was calculated. Besides lAAld, indole-3-aldehyde and phenylacetaldehyde served as substrates, but not acetaldehyde, propionaldehyde, salicylaldehyde, xanthine, hypoxanthine or catechol. Cyanide, dithionite and mercapto-ethanol totally inactivated the enzyme depending upon the concentration and duration of treatment. X-ray irradiation up to a dosage of 2900 r promoted the lAAld oxidizing activity of cell-free preparations made from irradiated coleoptiles. As yet, no cofactor requirements have been found for the activity. The enzyme is unlikely to be a pyridino- or a flavoprotein.