Decarboxylation Of Tyrosine Research Articles

Seven New Alkaloids Isolated from Marine Flavobacterium Tenacibaculum discolor sv11.

Marine flavobacterium Tenacibaculum discolor sv11 has been proven to be a promising producer of bioactive nitrogen-containing heterocycles. A chemical investigation of T. discolor sv11 revealed seven new heterocycles, including the six new imidazolium-containing alkaloids discolins C-H (1–6) and one pyridinium-containing alkaloid dispyridine A (7). The molecular structure of each compound was elucidated by analysis of NMR and HR-ESI-MS data. Furthermore, enzymatic decarboxylation of tryptophan and tyrosine to tryptamine and tyramine catalyzed by the decarboxylase DisA was investigated using in vivo and in vitro experiments. The antimicrobial activity of the isolated compounds (1–7) was evaluated. Discolin C and E (1 and 3) exhibited moderate activity against Gram-positive Bacillus subtilis DSM10, Mycobacterium smegmatis ATCC607, Listeria monocytogenes DSM20600 and Staphylococcus aureus ATCC25923, with MIC values ranging from 4 μg/mL to 32 μg/mL.

Molecular Identification of Endophytic Bacteria in Leucojum aestivum In Vitro Culture, NMR-Based Metabolomics Study and LC-MS Analysis Leading to Potential Amaryllidaceae Alkaloid Production.

In this study, endophytic bacteria belonging to the Bacillus genus were isolated from in vitro bulblets of Leucojum aestivum and their ability to produce Amaryllidaceae alkaloids was studied. Proton Nuclear Magnetic Resonance (1H NMR)-based metabolomics combined with multivariate data analysis was chosen to compare the metabolism of this plant (in vivo bulbs, in vitro bulblets) with those of the endophytic bacteria community. Primary metabolites were quantified by quantitative 1H NMR (qNMR) method. The results showed that tyrosine, one precursor of the Amaryllidaceae alkaloid biosynthesis pathway, was higher in endophytic extract compared to plant extract. In total, 22 compounds were identified including five molecules common to plant and endophyte extracts (tyrosine, isoleucine, valine, fatty acids and tyramine). In addition, endophytic extracts were analyzed using Liquid Chromatography-Mass Spectrometry (LC-MS) and Gas Chromatography-Mass Spectrometry (GC-MS) for the identification of compounds in very low concentrations. Five Amaryllidaceae alkaloids were detected in the extracts of endophytic bacteria. Lycorine, previously detected by 1H NMR, was confirmed with LC-MS analysis. Tazettine, pseudolycorine, acetylpseudolycorine, 1,2-dihydro-chlidanthine were also identified by LC-MS using the positive ionization mode or by GC-MS. In addition, 11 primary metabolites were identified in the endophytic extracts such as tyramine, which was obtained by decarboxylation of tyrosine. Thus, Bacillus sp. isolated from L. aestivum bulblets synthesized some primary and specialized metabolites in common with the L. aestivum plant. These endophytic bacteria are an interesting new approach for producing the Amaryllidaceae alkaloid such as lycorine.

Tyramine and amyloid beta 42: A toxic synergy

AbstractBackgroundIn synaptic cleft, trace amines play a crucial role as neurotransmitter signaling through the trace amine associated receptors. Tyramine, an important trace amine formed by decarboxylation of tyrosine, has been reported to be implicated in various diseases including schizophrenia, Parkinson's disease, migraine and Huntington's disease. However, there are no investigations to find its connection with Alzheimer's disease (AD).MethodGenetically modified Saccharomyces cerevisiae BY4743 producing different forms of amyloid beta 42 (Aβ42) peptide including native Aβ42 and green fluorescent protein (GFP) fused to Aβ42 were treated with various concentrations of tyramine. Reactive oxygen species (ROS) produced in these strains were measured using 2′,7′‐dichlorodihydrofluorescein diacetate (H2DCF‐DA) staining in a flow cytometric analysis. Growth inhibition of the yeast strains producing GFP and GFP‐Aβ42 were analysed in presence of tyramine. Petites generated due to tyramine were estimated in both these strains and petite frequency calculated.ResultTyramine was found to induce ROS formation in S. cerevisiae BY4743 as well as its genetically modified variants. ROS formation in yeast strains producing native Aβ42 treated with tyramine was significantly synergistically higher as compared to experimental controls. Similarly, yeast strains producing GFP‐Aβ42 was found to be inhibited more in media containing ethanol as sole carbon source compared to GFP producing controls in presence of 3 mM tyramine. Additionally, petite frequency in yeast strains producing GFP‐Aβ42 were found to increase significantly from around 20% to nearly 80% when grown in presence of tyramine.ConclusionThese findings suggest that tyramine in presence of Aβ42 is synergistically toxic to yeast cells by inducing ROS formation and causing petite mutation, implying possible cause of mitochondrial damage evident in AD patients. The study also demonstrates yeast as model to study compounds that have potential to exacerbate AD.

Expression of the Tyrosine Hydroxylase Gene from Rat Leads to Oxidative Stress in Potato Plants.

Catecholamines are biogenic aromatic amines common among both animals and plants. In animals, they are synthesized via tyrosine hydroxylation, while both hydroxylation or decarboxylation of tyrosine are possible in plants, depending on the species, though no tyrosine hydroxylase—a counterpart of the animal enzyme—has been identified yet. It is known that in potato plants, it is the decarboxylation of tyrosine that leads to catecholamine production. In this paper, we present the effects of the induction of an alternative route of catecholamine production by introducing the tyrosine hydroxylase gene from rat. We demonstrate that an animal system can be used by the plant. However, it does not function to synthesize catecholamines. Instead, it leads to elevated reactive oxygen species content and a constant stress condition in the plant, which responds with elevated antioxidant levels and improved resistance to infection.

Anti-tyramine potential of Lactobacillus rhamnosus (LGG®) in cheese samples collected from Alexandria, Egypt

ABSTRACT Tyramine is generated by decarboxylation of tyrosine through tyrosine decarboxylase enzyme produced by bacteria in fermented food including different cheese types. In the current study, 27 cheese samples were collected from local markets in Alexandria, Egypt, and analyzed for the prevalence of tyramine-producing bacteria by PCR using degenerate primers (DEC5/DEC3). A probiotic, Lactobacillus rhamnosus LGG® was evaluated for its ability to inhibit tyramine production in these isolates by High-Performance Liquid Chromatography (HPLC) analysis. A total of 31 strains harbored tyrosine decarboxylase gene with the identification of novel tyramine-producing strains including Macrococcus caseolyticus, Bacillus vallismortis, Bacillus cereus, Staphylococcus sciuri, and Staphylococcus pasteuri. L. rhamnosus LGG® suppressed the growth of 81% of the studied tyraminogenic strains. It completely inhibited the tyramine production in B. vallismortis with a decline of 99.4% and 50% in tyramine production in S. saprophyticus, and S. pasteuri, respectively. These results indicated the promising application of L. rhamnosus to reduce tyramine production in cheese products, a goal that has been regarded as a challenge by manufacturers.

Isolation and Molecular Identification of a Novel Tyramine-producing Bacterium, <i>Rummeliibacillus pycnus</i>

Decarboxylation of tyrosine through tyrosine decarboxylase enzyme produces tyramine which may represent a serious threat to public health, as it may cause severe toxicological effects. Intake of tyramine will invariably result in acute symptoms as it can rapidly gain access to the bloodstream and to various organs where it can act as a vasoactive agent through interaction with the sympathetic noradrenergic nerve terminals innervating cardiac and vascular smooth muscle tissues. This research is focusing on tyramine as one of the indicators of inappropriate food storage and processing conditions of milk products. In the current study, 25 dairy product samples were collected from local markets in Alexandria, Egypt, and were analyzed for bacterial contamination and prevalence of tyramine-producing bacteria by PCR using degenerate primers (DEC5/DEC3). While cream was the most contaminated dairy product, balady yogurt samples were the least contaminated ones. Different types of tyraminogenic bacteria have been isolated from the collected dairy products. Cream samples were contaminated with the widest variety of tyraminogenic bacteria among the isolated samples including Bacillus pumilis, Escherichia coli, Enterococcus faecium, and Proteus mirabilis. A total of 35 strains harboring tyrosine decarboxylase gene were detected with the identification of a novel tyramine-producing strain: Rummeliibacillus pycnus. These results indicate the promising application of degenerate primers (DEC5/DEC3) to detect tyramine production in dairy products, a goal that has been regarded as a challenge by manufacturers.

Crystal structures clarify cofactor binding of plant tyrosine decarboxylase

Plant tyrosine decarboxylase (TyrDC) is a group II pyridoxal 5′-phosphate (PLP)-dependent decarboxylase that mainly catalyzes the decarboxylation of tyrosine to tyramine. This is biologically important for diverting essential primary metabolites into secondary metabolic pathways. Intensive studies have characterized the effective of PLP-binding and the substrate specificity of mammalian 3,4-dihydroxyphenyl-l-alanine (Dopa) decarboxylases, a member of group II PLP-dependent decarboxylase. However, the characteristics of PLP binding and substrate specificity of plant TyrDCs remain unknown. In this study, we focus on the PLP binding manner, and determined the crystal structures of the apo and PLP binding form of type II TyrDC from Papaver somniferum (PsTyrDCII and PsTyrDCII-PLP). The structures showed that, unlike mammalian Dopa decarboxylase, the binding of PLP does not induce distinct conformational changes of PsTyrDCII regarding the overall structure, but the PLP binding pocket displays conformational changes at Phe124, His203 and Thr262. Combining structural comparation and the obtained biochemical findings, it is demonstrated that PsTyrDCII does not binds PLP tightly. Such characteristics of PLP binding may be required by its catalytic reaction and substrate binding. The activity of TyrDC probably regulated by the concentration of PLP in cells.

Application of end-point PCR technique to detect bacteria encoding tyrosine decarboxylase (TDC) gene in scombridae fish

Tuna, little tuna, and skipjack can form tyramine from decarboxylation of tyrosine by tyrosine decarboxylase (TDC) enzyme. High tyramine level in fish could cause toxicological effects. Early detection of the tyramine-forming bacteria by using DNA-based methods is needed for seafood safety assurance because it is more sensitive, specific, and faster. This study was aimed to obtain bacterial isolates, detection of TDC and 16S rRNA genes and identifying species of bacteria that encode TDC and 16S rRNA genes. The methods of this study included several steps including bacterial cultivation, DNA isolation and amplification of TDC and 16S rRNA gene markers as well as sequencing of amplicons. Bacterial DNA isolates were successfully obtained from samples by cultivation method. The TDC gene was successfully amplified and identified as belong to Carnobacterium genus, whereas the 16S rRNA gene belong to Enterobacter tabaci, E. hormaechei, Escherichia marmotae, and Peptoniphilus genus. The DNA-based method targeted tyrosine decarboxylase gene can be applied for early detection of biogenic amine accumulation in fishery products.

Highly Variable Pharmacokinetics of Tyramine in Humans and Polymorphisms in OCT1, CYP2D6, and MAO-A.

Tyramine, formed by the decarboxylation of tyrosine, is a natural constituent of numerous food products. As an indirect sympathomimetic, it can have potentially dangerous hypertensive effects. In vitro data indicated that the pharmacokinetics of tyramine possibly depend on the organic cation transporter OCT1 genotype and on the CYP2D6 genotype. Since tyramine is a prototypic substrate of monoamine oxidase A (MAO-A), genetic polymorphisms in MAO-A may also be relevant. The aims of this study were to identify to what extent the interindividual variation in pharmacokinetics and pharmacodynamics of tyramine is determined by genetic polymorphisms in OCT1, CYP2D6, and MAO-A. Beyond that, we wanted to evaluate tyramine as probe drug for the in vivo activity of MAO-A and OCT1. Therefore, the pharmacokinetics, pharmacodynamics, and pharmacogenetics of tyramine were studied in 88 healthy volunteers after oral administration of a 400 mg dose. We observed a strong interindividual variation in systemic tyramine exposure, with a mean AUC of 3.74 min*µg/ml and a high mean CL/F ratio of 107 l/min. On average, as much as 76.8% of the dose was recovered in urine in form of the MAO-catalysed metabolite 4-hydroxyphenylacetic acid (4-HPAA), confirming that oxidative deamination by MAO-A is the quantitatively most relevant metabolic pathway. Systemic exposure of 4-HPAA varied only up to 3-fold, indicating no strong heritable variation in peripheral MAO-A activity. Systolic blood pressure increased by more than 10 mmHg in 71% of the volunteers and correlated strongly with systemic tyramine concentration. In less than 10% of participants, individually variable blood pressure peaks by >40 mmHg above baseline were observed at tyramine concentrations of >60 µg/l. Unexpectedly, the functionally relevant polymorphisms in OCT1 and CYP2D6, including the CYP2D6 poor and ultra-rapid metaboliser genotypes, did not significantly affect tyramine pharmacokinetics or pharmacodynamics. Also, the MOA-A genotypes, which had been associated in several earlier studies with neuropsychiatric phenotypes, had no significant effects on tyramine pharmacokinetics or its metabolism to 4-HPAA. Thus, variation in tyramine pharmacokinetics and pharmacodynamics is not explained by obvious genomic variation, and human tyramine metabolism did not indicate the existence of ultra-low or -high MAO-A activity.

Structural Basis of the Substrate Specificity and Enzyme Catalysis of a Papaver somniferum Tyrosine Decarboxylase.

Tyrosine decarboxylase (TyDC), a type II pyridoxal 5′-phosphate decarboxylase, catalyzes the decarboxylation of tyrosine. Due to a generally high sequence identity to other aromatic amino acid decarboxylases (AAADs), primary sequence information is not enough to understand substrate specificities with structural information. In this study, we selected a typical TyDC from Papaver somniferum as a model to study the structural basis of AAAD substrate specificities. Analysis of the native P. somniferum TyDC crystal structure and subsequent molecular docking and dynamics simulation provide some structural bases that explain substrate specificity for tyrosine. The result confirmed the previous proposed mechanism for the enzyme selectivity of indolic and phenolic substrates. Additionally, this study yields the first crystal structure for a plant type II pyridoxal-5'-phosphate decarboxylase.

Biological Silages from Tunisian Shrimp and Octopus By-Products

ABSTRACTBiological silages were prepared from shrimp head and octopus viscera by-products recuperated from the Tunisian seafood industry. Physical and biochemical changes and microbiological profiles were determined for raw materials during fermentation and on end-products. Results showed that biological silage significantly affected (p < 0.05) moisture, protein, and ash contents of shrimp head (CSHS) and octopus viscera silages (COVS). CSHS and COVS were stable, and their final pH values were 4.31 ± 0.01 and 3.71 ± 0.00, respectively. Proteolysis activity was confirmed by a significant increase (p < 0.05) of soluble nitrogen and low molecular weight of protein (<260 Da) found on the end-products for both silages. Lipid oxidation was delayed by addition of 150 ppm ethoxyquin to the raw material prior to fermentation. Biogenic amines detected in raw shrimp and octopus samples decreased significantly (p < 0.05) during the silage process. Histamine and tyramine, detected at high levels on octopus viscera, were absent in the end-products. Tyramine was produced in CSHS, indicating the possibility of the bacterial decarboxylation of tyrosine. Microbiological profiles showed that both silage products were free from pathogenic and spoilage bacteria. Therefore, biological silage can be used as a conservation procedure of shrimp and octopus by-products. The storage period could be shorter than 30 days, and further analysis should be carried out to ascertain safety and nutritional value of silage products.

Lactobacillus casei strains isolated from cheese reduce biogenic amine accumulation in an experimental model

Tyramine and histamine are the biogenic amines (BAs) most commonly found in cheese, in which they appear as a result of the microbial enzymatic decarboxylation of tyrosine and histidine respectively. Given their toxic effects, their presence in high concentrations in foods should be avoided. In this work, samples of three cheeses (Zamorano, Cabrales and Emmental) with long ripening periods, and that often have high BA concentrations, were screened for the presence of BA-degrading lactic acid bacteria (LAB). Seventeen isolates were found that were able to degrade tyramine and histamine in broth culture. All 17 isolates were identified by 16S rRNA sequencing as belonging to Lactobacillus casei. They were typed by plasmid S1-PFGE and genomic macrorestriction-PFGE analysis. Two strains (L. casei 4a and 5b) associated with high degradation rates for both BAs were selected to test how this ability might affect histamine and tyramine accumulation in a Cabrales-like mini-cheese manufacturing model. The quantification of BAs and the monitoring of the strains' growth over ripening were undertaken by RP-HPLC and qPCR respectively. Both strains were found to reduce histamine and tyramine accumulation. These two strains might be suitable for use as adjunct cultures for reducing the presence of BAs in cheese.

Quantitative detection and identification of tyramine-producing enterococci and lactobacilli in cheese by multiplex qPCR

Tyramine is the most abundant biogenic amine in fermented dairy products, in which it is produced through the microbial enzymatic decarboxylation of tyrosine. This activity has been detected in a variety of lactic acid bacteria mainly belonging to the genera Enterococcus and Lactobacillus. This paper describes a culture-independent qPCR method, based on the specific amplification of the tdc gene, for the detection, quantification and identification of bacteria with the ability to produce tyramine. This method was found to be specific and to show a wide dynamic range, thus allowing the quantification of these tdc+ bacterial groups among the complex microbiota of cheese. tdc qPCR was used to follow the development of tdc+ microbiota during the manufacture of a blue-veined cheese (Cabrales) made from raw milk. In this type of cheese, tdc+ enterococci seem to be responsible for the high concentrations of tyramine detected. The method was also used to identify and quantify tdc+ enterococci and lactobacilli in 18 commercially available cheeses. Different types and numbers of these microorganisms were found. Their relationships with the concentration of tyramine and technological factors are discussed.

An enzymatic, stereoselective synthesis of (S)-norcoclaurine

An efficient, stereoselective, green synthesis of (S)-norcoclaurine (higenamine) has been developed using the recombinant (S)-norcoclaurine synthase (NCS) enzyme, starting from the cheap tyrosine and dopamine substrates in a one-pot, two step process. Key steps in the biotransformation consist of the oxidative decarboxylation of tyrosine by stoichiometric amounts of sodium hypochlorite in order to generate 4-hydroxyphenylacetadehyde, followed by the addition of enzyme and dopamine substrate in the presence of ascorbate, a necessary ingredient in order to avoid oxidation of the catechol moiety. Quantitative extraction of the product from an aqueous solution was achieved by adsorption onto active charcoal dispersed in the reaction mixture. The optimized process afforded enantiomerically pure (S)-norcoclaurine (93%) in a yield higher than 80% and allowed good recovery of the enzyme for recycling. The process thus developed represents the first example of a green Pictet–Spengler synthesis, which may pave the way to novel strategies in benzylisoquinoline alkaloid synthesis.

Tyramine biosynthesis in Enterococcus durans is transcriptionally regulated by the extracellular pH and tyrosine concentration

SummaryThe microbial decarboxylation of some amino acids leads to the undesirable presence of biogenic amines in foods. One of the most abundant and frequent biogenic amines found in fermented foods is tyramine, which is produced by the decarboxylation of tyrosine. In the present work, transcriptional analysis of tyramine biosynthesis in Enterococcus durans IPLA655, a strain isolated from cheese, was studied. The gene coding for the tyrosine decarboxylase (tdcA) and that coding for the tyrosine‐tyramine antiporter (tyrP) form an operon transcribed from the promoter PtdcA, the expression of which is regulated by the extracellular pH and tyrosine concentration. Quantification of gene expression during the log phase of growth showed high concentrations of tyrosine and acidic pH conditions to induce tdcA‐tyrP polycistronic messenger transcription.

Factors affecting tyramine production in Enterococcus durans IPLA 655

The decarboxylation of tyrosine by certain lactic acid bacteria leads to the undesirable presence of tyramine in fermented foods. Tyramine is the most frequent biogenic amine found in cheese and is also commonly found in other fermented foods and beverages. The tyramine-producing strain Enterococcus durans IPLA 655 was grown in a bioreactor under different conditions to determine the influence of carbon source, tyrosine and tyramine concentrations, and pH on tyramine production. The carbon source appeared to have no significant effect on the production of tyramine. In contrast, tyrosine was necessary for tyramine production, while the presence of tyramine itself in the growth medium inhibited such production. pH showed by far the greatest influence on tyramine synthesis; tyramine was produced in the greatest quantities at pH 5.0, although this was accompanied by a reduced growth rate.

Sequencing of the Tyrosine Decarboxylase Cluster of Lactococcus lactis IPLA 655 and the Development of a PCR Method for Detecting Tyrosine Decarboxylating Lactic Acid Bacteria

The enzymatic decarboxylation of tyrosine produces tyramine, the most abundant biogenic amine in dairy products—especially in cheeses. The screening of lactic acid bacteria isolated from different artisanal cheeses and a number of microbial collections identified 22 tyramine-producing strains belonging to different genera. The Lactococcus lactis strain IPLA 655 was selected, and the genes encoding a putative tyrosyl tRNA synthetase, a tyrosine decarboxylase (tdcA), and a tyrosine-tyramine antiporter, found together as a cluster, were sequenced. The disruption of tdcA yielded a strain unable to produce tyramine. Comparison of the L. lactis IPLA 655 tdcA gene with database tdcA sequences led to the design of two primers for use in a PCR method that identified potential tyramine-producing strains. The proposed method can use purified DNA, isolated colonies, milk, curd, and even cheese as a template. Molecular tools for the rapid detection of tyramine-producing bacteria at any time during the fermentation process could help prevent tyramine accumulation in fermented foods. The proposed technique could be of great use to the food industry.

Enzymatic decarboxylation of tyrosine and phenylalanine to enhance volatility for high-precision isotopic analysis.

We present a rapid and selective method to increase the volatility of tyrosine and phenylalanine without adding derivative C for high-precision gas chromatography-continuous-flow isotope ratio mass spectrometry (GCC-IRMS) based on enzymatic decarboxylation to yield alkylamines and evaluated for 15N isotopic integrity. Purified tyrosine and phenylalanine were converted to tyramine and phenethylamine by tyrosine and phenylalanine decarboxylases, respectively. GC separation was achieved using a thick stationary phase (5-microm) capillary column. Recoveries were 95 +/- 2%. The reproducibility of delta15N of tyramine and phenethylamine measured by GCC-IRMS averaged SD(delta15N) = 0.33 per thousand. The absolute differences between delta15N of amino acids measured by elemental analyzer-IRMS and the alkylamines measured by GCC-IRMS was not significant. Phenethylamine and tyramine prepared from a mixture of 18 amino acids were extracted by ethanol with 95% recovery, and analysis yielded clean chromatograms and equivalent precision. These data indicate that enzymatic decarboxylation of phenylalanine and tyrosine is a convenient method to increase their volatility for continuous-flow isotopic analysis without introducing extraneous C or significant isotopic fractionation.

Metabolism of Tryptophan in the Liver: Interference with Decarboxylation of Other Aromatic Amino Acids

Decarboxylation of aromatic amino acid in mammalian tissues is catalyzed by aromatic amino acid decarboxylase (EC. 4.1.1.28, AAD). The enzyme differs in its affinity to individual aromatic amino acids, the best substrates being 3,4-dihydroxyphenylalanine (dopa) and 5-hydroxytroptophan. Surprisingly, AAD is abundant in the liver, where the substrates with rather low affinity to AAD as tryptophan, phenylalanine, and tyrosine are offered to decarboxylation. In the present paper, the possibility of interference of tryptophan with decarboxylation of phenylalanine, tyrosine as well as dopa in the liver was investigated. The AAD activity was measured radiometrically with 1-14C-labeled aromatic amino acid substrates using the rat liver enzyme. The influence of tryptophan on decarboxylation of tyrosine was formally competitive with Ki = 9.2 x 10(-3) M, while the inhibition of decarboxylation of phenylalanine by tryptophan was non-competitive with Ki at 2.75 x 10(-2) M. The effect of tryptophan on decarboxylation of dopa was small and it could not be expressed in terms of inhibition kinetics and inhibition constant. At physiological concentrations of aromatic amino acids in plasma, tryptophan does not seem to have remarkable effects on decarboxylation of phenylalanine, tyrosine, and dopa in the liver.

Purification and characterization of aromatic L-amino acid decarboxylase from rat kidney and monoclonal antibody to the enzyme.

Aromatic L-amino acid decarboxylase was purified from rat kidney to homogeneity, as judged by polyacrylamide gel electrophoresis, in the presence and absence of sodium dodecyl sulfate (SDS). The final preparation showed an activity of 3,4-dihydroxyphenylalanine (dopa) decarboxylation of approximately 11,000 nmol/min/mg of protein at 37 degrees C. The purified enzyme also catalyzed the decarboxylation of 5-hydroxytryptophan, tyrosine, tryptophan, and phenylalanine. The enzyme appeared to be composed of two identical subunits, each possessing a molecular weight of 48,000. The isoelectric point of the enzyme was estimated to be 6.7 in the presence of 8 M urea and 5.60-5.85 in its absence. To examine the identity of aromatic L-amino acid decarboxylase from various tissues, a monoclonal antibody directed against the enzyme from rat kidney was prepared. Immunotitration and analysis by antibody-affinity chromatography followed by SDS-polyacrylamide gel electrophoresis revealed that the enzymes from the striatum, adrenal medulla, pineal gland, liver, and kidney were indistinguishable with respect to immunological cross-reactivity and molecular size.