L-arginine Catabolism Research Articles

PULMONARY HYPERTENSION IN SICKLE CELL DISEASE: Relevance to Children

Pulmonary arterial hypertension (PAH), once considered a rare complication of sickle cell disease (SCD) and thalassemia, appears to be more common in adults with hemoglobinopathy than previously appreciated. On prospective screening of adults with SCD, approximately one-third of adults are found on echocardiography to have a tricuspid regurgitant jet velocity (TRV) of 2.5 m/s or higher, many of whom are asymptomatic. Dyspnea on exertion is the most common presenting symptom. This TRV abnormality is a marker for approximately 40% 3-year mortality in adults, and it is associated with laboratory values suggestive of more severe intravascular hemolysis. Release of hemoglobin and arginase from lysed red cells causes scavenging of nitric oxide (NO) and catabolism of L-arginine, the obligate substrate for NO synthase. The resulting impairment in NO bioavailability is associated with pulmonary vasoconstriction, endothelial dysfunction, thrombosis, and eventual development of plexogenic arterial lesions, the histological hallmark of all forms of PAH. Undoubtedly, additional pathophysiological mechanisms will also play a role in its multifactorial pathogenesis. Early data from children with SCD indicate a similar prevalence of elevated TRV, but the prognostic implications of this remain to be established. Individual patient diagnosis of PAH requires confirmation by right heart catheterization studies and individualized management. Hemolysis-associated PAH with impairments in NO bioavailability is being identified in thalassemia and other hemolytic disorders, and may be a general consequence of long-standing, severe intravascular hemolytic anemia.

Altered Nitric Oxide Synthase, Arginase and Ornithine Decarboxylase Activities, and Polyamine Synthesis in Response to Ischemia of the Rabbit Detrusor

Little is known about L-arginine catabolism following ischemia in the bladder. We examined the changes in nitric oxide synthase, arginase and ornithine decarboxylase activity, polyamine biosynthesis and the ability to produce nitric oxide following ischemia of the rabbit bladder. Bladder ischemia was created by ligation of a unilateral bladder artery. At various time points, that is 1, 4, 8, 24, 48 and 72 hours following ligation, the bladders were excised and harvested for determinations. Constitutive nitric oxide synthase, inducible nitric oxide synthase arginase and ornithine decarboxylase activities increased with time, peaking at 48 hours without significant differences between the ligated and nonligated sides in the whole layer. Arginase and ornithine decarboxylase increased mainly in the muscularis following ischemia. Also, putrescine in the muscularis was significantly higher than in the mucosa 48 hours following ischemia. Baseline nitrite/nitrate production in the whole detrusor on the ligated side at 24 hours was significantly lower than that in the normal detrusor. However, nor-hydroxyarginine as an arginase inhibitor and L-arginine increased nitrite/nitrate production in the ischemic detrusor without changing in the normal detrusor. This increasing effect of nor-hydroxyarginine was abolished by nitroarginine methylester as a nitric oxide synthase inhibitor. Enzymes related to L-arginine catabolism were involved in the early events of ischemic bladder. Arginase may have 2 independent roles, that is 1) activation of arginase/ornithine decarboxylase/polyamines pathways in the muscle injury and remodeling following ischemia, and 2) endogenous negative regulation of nitric oxide production by limiting the L-arginine substrate for nitric oxide synthase.

Arginase and polyamine synthesis are key factors in the regulation of experimental leishmaniasis in vivo

Arginase 1, an enzyme induced by Th2 cytokines, is a hallmark of alternatively activated macrophages and is responsible for the hydrolysis of L-arginine into ornithine, the building block for the production of polyamines. Upregulation of arginase 1 has been observed in a variety of diseases, but the mechanisms by which arginase contributes to pathology are not well understood. We reveal here a unique role for arginase 1 in the pathogenesis of nonhealing leishmaniasis, a prototype Th2 disease, and demonstrate that the activity of this enzyme promotes pathology and uncontrolled growth of Leishmania parasites in vivo. Inhibition of arginase activity during the course of infection has a clear therapeutic effect, as evidenced by markedly reduced pathology and efficient control of parasite replication. Despite the clear amelioration of the disease, this treatment does not alter the Th2 response. To address the underlying mechanisms, the arginase-induced L-arginine catabolism was investigated and the results demonstrate that arginase regulates parasite growth directly by affecting the polyamine synthesis in macrophages.

Consumption of L-arginine mediated by Entamoeba histolytica L-arginase (EhArg) inhibits amoebicidal activity and nitric oxide production by activated macrophages.

In this study we discuss the cloning and expression of Entamoeba histolytica arginase (EhArg), an enzyme that catalyses the hydrolysis of L-arginine to L-ornithine and urea. L-norvaline, a competitive inhibitor of E. histolytica L-arginase, inhibits the growth of the parasite, which suggests that the catabolism of L-arginine mediated by EhArg is essential. Nitric oxide (NO) is an antimicrobial agent that inhibits some key enzymes in the metabolism of Entamoeba histolytica. NO is synthesized by activated macrophages from L-arginine, the substrate of NO synthase (NOS-II). We show that E. histolytica inhibits NO mediated amoebicidal activity of activated macrophages by consuming L-arginine present in the medium.

Mechanistic and metabolic inferences from the binding of substrate analogues and products to arginase.

Arginase is a binuclear Mn(2+) metalloenzyme that catalyzes the hydrolysis of L-arginine to L-ornithine and urea. X-ray crystal structures of arginase complexed to substrate analogues N(omega)-hydroxy-L-arginine and N(omega)-hydroxy-nor-L-arginine, as well as the products L-ornithine and urea, complete a set of structural "snapshots" along the reaction coordinate of arginase catalysis when interpreted along with the X-ray crystal structure of the arginase-transition-state analogue complex described in Kim et al. [Kim, N. N., Cox, J. D., Baggio, R. F., Emig, F. A., Mistry, S., Harper, S. L., Speicher, D. W., Morris, Jr., S. M., Ash, D. E., Traish, A. M., and Christianson, D. W. (2001) Biochemistry 40, 2678-2688]. Taken together, these structures render important insight on the structural determinants of tight binding inhibitors. Furthermore, we demonstrate for the first time the structural mechanistic link between arginase and NO synthase through their respective complexes with N(omega)-hydroxy-L-arginine. That N(omega)-hydroxy-L-arginine is a catalytic intermediate for NO synthase and an inhibitor of arginase reflects the reciprocal metabolic relationship between these two critical enzymes of L-arginine catabolism.

Interrelation between cyanophycin synthesis, L-arginine catabolism and photosynthesis in the cyanobacterium Synechocystis sp. strain PCC 6803.

Ultrastructural and immunocytochemical investigations gave evidence that cyanophycin (multi-L-arginyl-poly-L-aspartate) granules accumulate in the cyanobacterium Synechocystis sp. strain PCC 6803 under nutrient deficient growth conditions, especially under phosphate limitation. Besides nutrient deficiency, growth of Synechocystis PCC 6803 on L-arginine or L-asparagine as sole N-source also led to high increase of cyanophycin synthesis, while growth on the combination of L-arginine or L-asparagine with nitrate only caused minor cyanophycin accumulation. Growth of Synechocystis PCC 6803 on L-arginine as sole N-source caused substantial morphological and physiological changes, such as severe thylakoid membrane degradation with partial loss of pigments and photosynthetic activity leading to a phenotype almost like that seen under nutrient deficiency. In contrast to the wild type, the PsbO-free Synechocystis PCC 6803 mutant could grow on L-arginine as sole N-source with only minor morphological and physiological changes. Due to its fairly balanced growth, the mutant accumulated only few cyanophycin granules. L-arginine degrading activity (measured as ornithine and ammonium formation) was high in the PsbO-free mutant but not in the wild type when cells were grown on L-arginine as sole N-source. In both cells types the L-arginine degrading activity was high (although in the PsbO-free mutant about twice as high as in wild type), when cells were grown on L-arginine in combination with nitrate, and as expected very low when cells were grown on nitrate as sole N-source. Thus, net cyanophycin accumulation in Synechocystis PCC 6803 is regulated by the relative concentration of L-arginine to the total nitrogen pool, and the intracellular L-arginine concentration is greatly influenced by the activity of the L-arginine degrading enzyme system which in part is regulated by the activity status of photosystem II. These results suggest a complex interrelation between cyanophycin synthesis, L-arginine catabolism, and in addition photosynthesis in Synechocystis PCC 6803.

Physiological cyclic stretch directs L-arginine transport and metabolism to collagen synthesis in vascular smooth muscle.

Application of cyclic stretch (10% at 1 hertz) to vascular smooth muscle cells (SMC) increased L-arginine uptake and this was associated with a specific increase in cationic amino acid transporter-2 (CAT-2) mRNA. In addition, cyclic stretch stimulated L-arginine metabolism by inducing arginase I mRNA and arginase activity. In contrast, cyclic stretch inhibited the catabolism of L-arginine to nitric oxide (NO) by blocking inducible NO synthase expression. Exposure of SMC to cyclic stretch markedly increased the capacity of SMC to generate L-proline from L-arginine while inhibiting the formation of polyamines. The stretch-mediated increase in L-proline production was reversed by methyl-L-arginine, a competitive inhibitor of L-arginine transport, by hydroxy-L-arginine, an arginase inhibitor, or by the ornithine aminotransferase inhibitor L-canaline. Finally, cyclic stretch stimulated collagen synthesis and the accumulation of type I collagen, which was inhibited by L-canaline. These results demonstrate that cyclic stretch coordinately stimulates L-proline synthesis by regulating the genes that modulate the transport and metabolism of L-arginine. In addition, they show that stretch-stimulated collagen production is dependent on L-proline formation. The ability of hemodynamic forces to up-regulate L-arginine transport and direct its metabolism to L-proline may play an important role in stabilizing vascular lesions by promoting SMC collagen synthesis.

Vascular effects of endothelin-1 in essential hypertension: relationship with cyclooxygenase-derived endothelium-dependent contracting factors and nitric oxide.

Endothelium plays a primary role in the local modulation of vascular function and structure by the production and release of several substances including nitric oxide and endothelins (ET). Nitric oxide is a labile substance produced from the catabolism of L-arginine and not only causes vessel relaxation, but also inhibits platelet aggregation, smooth muscle cell proliferation, monocyte adhesion, adhesion molecules expression and endothelin-1 (ET-1) production. Endothelium-derived ET-1 is a potent vasoconstrictor and has inotropic and mitogenic properties. ET-1 acts through smooth muscle ET(A) and ET(B) receptors, which mainly mediate vasoconstriction, and endothelial ET(B) receptors, which oppose ET(A)- and ET(B)-mediated vasoconstriction by stimulating nitric oxide formation. Both nitric oxide and ET-1 play a crucial role in the cardiovascular physiology and an alteration of these systems can be a promoter of or be associated with most cardiovascular diseases. Essential hypertension is a pathological condition characterized by endothelial dysfunction. In hypertensive patients nitric oxide availability is impaired because of the production of cyclooxygenase-derived vasoconstrictor substances. The latter may also mediate the vasoconstrictor response to exogenous ET-1 because in forearm circulation of essential hypertensives, but not of normotensive controls, the ET-1-induced vasoconstriction is significantly blunted by intrabrachial indomethacin. Therefore, in normotensive subjects and essential hypertensives the vasoconstrictor effect of ET-1 seems to be dependent on different mechanisms. Moreover, in the peripheral circulation of normotensive subjects, where tonic nitric oxide production is preserved, unselective ET(A/B), receptor blockade by TAK-044 causes a very modest degree of vasodilation. In contrast in essential hypertensives, where the tonic nitric oxide production is reduced, the vasodilating effect of TAK-044 is more evident, indicating that the predominant vascular effect of endogenous ET-1 is the vasoconstriction. A possible explanation for this finding, in addition to an increased production of the peptide, could be related to a reduced ET(B) receptor-mediated nitric oxide activation. These peculiar aspects of the role of ET-1 in essential hypertension could have physiopathological relevance.

Lysophosphatidylcholine Regulates Cationic Amino Acid Transport and Metabolism in Vascular Smooth Muscle Cells: ROLE IN POLYAMINE BIOSYNTHESIS

Lysophosphatidylcholine (lyso-PC) is a major component of atherogenic lipids that stimulate vascular smooth muscle cell (SMC) proliferation. Because cationic amino acids are metabolized to growth-stimulatory polyamines, we examined whether lyso-PC regulates the transcellular transport and metabolism of cationic amino acids by vascular SMC. Treatment of SMC with lyso-PC initially (0-2 h) decreased cationic amino acid uptake, whereas longer exposures (6-24 h) progressively increased transport. Kinetic studies indicated that lyso-PC-induced inhibition was associated with a decrease in affinity for cationic amino acids, but the stimulation was mediated by an increase in transport capacity. Lyso-PC strongly induced the expression of cationic amino acid transporter-2 mRNA while modestly elevating the level of cationic amino acid transporter-1 mRNA. In addition, lyso-PC stimulated intracellular cationic amino acid metabolism by inducing ornithine decarboxylase activity and mRNA expression and also by inducing arginase activity in vascular SMC. In contrast, lyso-PC inhibited the catabolism of L-arginine to nitric oxide by blocking inducible nitric oxide synthase expression. Lyso-PC increased markedly the capacity of SMC to generate putrescine, a polyamine, from extracellular L-ornithine and L-arginine. The lyso-PC-mediated increase in the production of putrescine was reversed by NG-methyl-L-arginine, a competitive inhibitor of cationic amino acid transport, or by alpha-difluoromethylornithine, an ornithine decarboxylase inhibitor. The formation of putrescine from L-arginine was also prevented by arginase inhibitor NG-hydroxy-L-arginine. These results demonstrate that lyso-PC stimulates polyamine synthesis in vascular SMC by inducing the expression of the genes that regulate both the transport and metabolism of cationic amino acids. The actions of lyso-PC in stimulating cationic amino acid uptake and directing their metabolism to growth-stimulatory polyamines while simultaneously inhibiting the synthesis of antiproliferative NO, may contribute to lyso-PC-induced SMC proliferation and atherosclerotic lesion formation.

Arginine metabolism in rat enterocytes

Rat enterocytes exposed to l-arginine in the absence of any other exogenous substrate were found to actively metabolize this cationic amino acid. l-Arginine was converted to l-citrulline either directly in a NADPH-sensitive manner thought to be coupled with the generation of NO, or indirectly through the sequence of reactions catalyzed by arginase and ornithine transcarbamylase. A large fraction of l-citrulline and l-ornithine generated from exogenous l-arginine was released in the incubation medium. The production of CO 2 and (poly)amines from l-arginine occurred at rates 2 to 3 orders of magnitude lower than that characterizing the net uptake of the cationic amino acid, and this despite the fact that enterocytes were equipped to allow the interconversion of l-ornithine and l-glutamate. It is concluded that the oxidative catabolism of l-arginine in enterocytes is quantitatively negligible relative to its conversion to l-citrulline and l-ornithine.

Metabolic and secretory response of parotid cells to cationic amino acids. Uptake and catabolism of L-arginine and L-ornithine

L-Arginine and L-ornithine, which stimulate amylase release, are taken up by rat parotid cells. L-Arginine is converted, in an NADPH-dependent manner and to a limited extent to L-citrulline in parotid cell homogenates, despite the absence of ornithine transcarbamylase activity. L-Arginine is largely converted to urea and L-ornithine. The generation of putrescine and polyamines from L-ornithine occurs at a very low rate, relative to the cell content in preformed amines. The major fate of exogenous or arginine-derived ornithine consists in its conversion to L-glutamate, which is then further metabolized. These findings raise several hypotheses for the secretory response of the parotid cells to cationic amino acids, including their accumulation as positively charged molecules inside the cell and the generation of either NO, amines, substrates for a transglutaminase-catalyzed reaction, or ATP through oxidative catabolism. However, each of these hypotheses meets with objections, the modality for the stimulation of amylase release by cationic amino acids being eventually considered as an unsettled matter.

Investigations about various Possible Functions of the L -Amino Acid Oxidase in the Cyanobacterium Anacystis nidulans

Abstract The cyanobacterium A nacystis nidulans was grown on nitrate or L-arginine as sole nitrogen source and in the presence of different divalent cation concentrations (1 mᴍ MgSO4 and 0.1 mᴍ CaCl2 or 0.1 mᴍ MgSO4 and 0.05 mᴍ CaCl2). The L-amino acid oxidase previously reported to be present in Anacystis nidulans (E . K. Pistorius and A. E. Gau, Biochim. Biophys. Acta 849, 203, 1986) was shown to be involved in L-arginine catabolism in cells grown with the lower divalentcation concentration. Under these conditions L-arginine was partly degraded via 2-ketoarginine and 4-guanidinobutyrate. On the other hand, at higher cation concentrations the ʟ-amino acid oxidase activity seem ed to be not sufficient to provide enough NH4 + from ʟ-arginine for cell growth. Under those conditions photosystem II activity was initially reduced, and growth on ʟ-arginine could only start after photosystem II activity increased again and after arginase was induced. The arginase pathway was functional in A . nidulans grown on ʟ-arginine independently of the divalent cation concentration in the medium. A tentative scheme of the various functiona roles of the ʟ-amino acid oxidase protein in A . nidulans is given. This model combines the here presented and the previous results and suggests that the ʟ-amino acid oxidase is functional in photosynthetic and respiratory activities as well as in ʟ-arginine degradation in A . nidulans. All these activities of the ʟ-amino acid oxidase protein are greatly influenced by the divalent cation concentration in the growth medium.

The γ-guanidinobutyramide pathway of l-arginine catabolism in Leishmania donovani promastigotes

l-Arginine stimulates the respiration of Leishmania donovani to rates comparable to those observed with d-glucose. γ-Guanidinobutyramide, CO 2, urea and succinate have been identified as products of l-arginine catabolism by the cell-free extract. The reactions involved in CO 2 and urea formation require aerobic conditions. An enzymatic reaction that converts radiolabelled l-arginine to γ-guanidinobutyramide occurs in cell-free extracts. The enzyme catalyzes a reaction in which O 2 consumption and CO 2 production are equimolar. The O 2 uptake and CO 2 production are stimulated by Mg 2+, Mn 2−, FMN, pyridoxal phosphate, and inhibited by hydroxylamine and NaBH 4. l-Arginine decarboxyoxidase is suggested as the trivial name for this enzyme. The enzyme has maximum activity at pH 6.7, and its K m for l-arginine is 3.8 mM. l-Arginine decarboxyoxidase initiates the catabolism of l-arginine (pH ⩽ 7) in this species, and is followed by the other enzymes of γ-guanidinobutyramide pathway. Assay procedures have been devised to assay the multiple enzymes of this pathway.

Argininstoffwechsel in Fruchtkörpern und Myzel von Partus tigrinus

Summary The metabolism of L-arginine was investigated in fruit-bodies and mycelium of a culture of the fungus Panus tigrinus free of arginase activity. After feeding of 14C-labelled L-arginine the catabolism of L-arginine by decarboxylation or transamidination was influenced by the culture medium. Varying the substrate concentration results in a change of the relative proportion of both pathways of L-arginine catabolism. High amounts of L-arginine caused an increase in transamidination whereas a low arginine concentration affected decarboxylation and transamination of L-arginine in particular. After simultaneous application of varied amounts of [14C-amidine]-L-arginine and γ-amino-butyric acid, which is the product of both pathways and the acceptor of transamidination, results showed that the catabolism of L-arginine via transamidination is preferred (formation of arcaine). Catabolism of L-arginine by decarboxylation, transamidination and transamination was also observed in the vegetative mycelium. Dependent on the age of the mycelium the same compounds were found after 10, 15 and 21 days after incubation, but the relative proportion of the pathways was different from that of the fruit-bodies.

Physiological consequences of starvation in Pseudomonas putida: degradation of intracellular protein and loss of activity of the inducible enzymes of L-arginine catabolism.

We investigated the degradation of radioisotopically labeled intracellular protein in starved, intact cells of Pseudomonas putida P2 (ATCC 25571) and the regulation of this process. Intracellular protein isotopically labeled with L-[4,5-3H]leucine during log-phase growth at 30 C is degraded at rates of 1 to 2%/h in log-phase cells and 7 to 9%/h in starved cells. Rifampin, chloramphenicol, and tosyllysine chloromethylketone lower the rate of protein degradation by starved cells. Addition to starved cells of a nutrient upon which the culture is induced for growth rapidly lowers the rate of protein degradation from 7 to 9%/h to less than 1.5%/h. A nutrient that is oxidized but that cannot immediately support growth also lowers the rate of starvation-induced protein degradation. Proteolytic activity of cell extracts requires a divalent metal ion and may be inhibited up to 60% by tosyllysine chloromethylketone or p-toluenesulfonyl fluoride. Rifampin and chloramphenicol have no effect. In contrast to intact cells, extracts of growing or starving cells degrade protein at equivalent rates. We also investigated the stabilities of the inducible transport system and of four inducible intracellular enzymes of L-arginine catabolism. These include: the membrane-associated, L-arginine-specific transport system; L-arginine oxidase (oxidase); alpha-ketoarginine decarboxylase (decarboxylase); gamma-guanidinobutyraldehyde dehydrogenase ( dehydrogenase); and gamma-guanidinobutyrate amidinohydrolase (hydrolase). In starved cells, the rates of loss of activities were: transport and dehydrogenase activities, stable; oxidase and decarboxylase activities, 20 to 30%/h; hydrolase activity, 5 to 8%/h. Chloramphenicol decreases the rate of loss of oxidase, decarboxylase, and hydrolase activity, whereas p-toluenesulfonyl fluoride lowers the rate of loss of decarboxylase but not of oxidase or hydrolase activity. Addition to starved cells of a nutrient for which they are already induced for growth (e.g., malate, a noninducer of arginine catabolic enzymes) decreases the rate of loss of oxidase and decarboxylase activity but not that of the hydrolase.

Dual role for N-2-acetylornithine 5-aminotransferase from Pseudomonas aeruginosa in arginine biosynthesis and arginine catabolism

In Pseudomonas aeruginosa N-2-acetylornithine 5-aminotransferase (ACOAT), the fourth enzyme of arginine biosynthesis is induced about 15-fold by cultivating the organism on a medium with L-arginine as the sole carbon and nitrogen source. Synthesis of the enzyme is subject to catabolite repression and nitrogen source. Synthesis of the enzyme is subject to catabolite repression by a variety of carbon sources. ACOAT from strain PAO 1 was purified over 40-fold to electrophoretic homogeneity. A molecular weight of approximately 110,000 was obtained by thin-layer gel filtration. Electrophoresis in sodium dodecyl sulfate gels gave a single band corresponding to a molecular weight of 55,000. Purified ACOAT catalyzes the transamination of N-2-acetyl-L-ornithine as well as of L-ornithine with 2-oxoglutarate (Km values of 1.1, 10.0, and 0.7 mM, respectively). With N-2-acetyl-L-ornithine as amino donor, the pH-optimum of the enzymatic reaction is 8.5; with L-ornithine as amino donor, 9.5. The catalytic properties of ACOAT as well as the regulation of its synthesis indicate that in P. aeruginosa this enzyme functions in the biosynthesis as well as in the catabolism of L-arginine.

Metabolism of Basic Amino Acids in Pseudomonas putida

Abstract γ-Guanidinobutyrate amidinohydrolase, the third enzyme of l-arginine catabolism in Pseudomonas putida, has been purified 68-fold from extracts of cultures grown on l-arginine. Synthesis of the amidinohydrolase is induced by growth on l-arginine or γ-guanidinobutyrate, but not by growth on γ-aminobutyrate or on urea plus dl-malate. Hydrolysis of γ-guanidinobutyrate to γ-aminobutyrate and urea proceeds essentially to completion at pH 7 to 11. The purified enzyme specifically requires Mn2+ and exhibits optimum activity at about pH 10 and 50°. The Km for γ-guanidinobutyrate is 32 mm at pH 10. While δ-guanidinovalerate and e-guanidinocaproate also are hydrolyzed, the value of both Km (δ-guanidinovalerate = 206 mm; e-guanidinocaproate = 163 mm) and of Vmax (606, 27, and 11 e.u. per mg for γ-guanidinobutyrate, δ-guanidinovalerate, and e-guanidinocaproate, respectively) suggest that γ-guanidinobutyrate is the natural substrate. The molecular weight of the purified enzyme was estimated to be 178,000 by gel permeation chromatography and 190,000 by sucrose density gradient centrifugation.

Catabolism of L-arginine by entrapped cells of Streptococcus faecalis ATCC 8043

1. 1. It has been established that microbial cells can be entrapped in a polymeric matrix to study metabolic process by flowing solutions of substrate through the resulting gel. Polymer gel entrapment of Streptococcus faecalis ATCC 8043 cells or cellular material was accomplished by an in situ polymerization of acrylamide and N, N′-methylenebisacrylamide. The resulting entrapped cells wer able to convert arginine to catabolic products via the arginine dihydrolase pathway. The catabolic products observed depended upon the state of the cell. An entrapped frozen cell paste produced citrulline. Entrapped whole cell preparations produced ornithine and putrescine; the production of putrescine was dependent upon the growth history of the cells as well as the pH of the substrate solution. No citrulline was recovered from entrapped who cell preparations. 2. 2. Electron photomicrographic evidence was obtained which shows that the cells remain intact during polymerization and subsequent use. The intact cell wall of the polymer entrapped microorganism can be distrupted by lysozyme. Cell fragments and nuclear material from the disrupted cells diffused out of the gel to yield a polymer-matrix no longer able to catabolize arginine.

Metabolism of Basic Amino Acids in Pseudomonas putida: INTERMEDIATES IN l-ARGININE CATABOLISM

Abstract Growth of Pseudomonas putida P2 (ATCC 25571) on l-arginine as the sole source of carbon and nitrogen induces synthesis of the enzymes of a catabolic pathway for arginine similar to that found in Streptomyces griseus, but with a different first intermediate. The catabolic sequence in this pathway is: l-arginine → α-ketoarginine → γ-guanidinobutyrate → γ-aminobutyrate. Isotope from l-[U-14C]arginine is incorporated into trapping pools of all three intermediates and isotope from α-keto[U-14C]arginine is incorporated into pools of γ-guanidinobutyrate and γ-aminobutyrate. Cell-free extracts of cultures grown on l-arginine are induced for the evolution of ammonia from l-arginine, for the evolution of CO2 from α-ketoarginine, and for the hydrolytic removal of urea from γ-guanidinobutyrate. Cultures grown on dl-malate and exposed to l-arginine induce the synthesis of an l-arginine uptake system and of three enzymes of l-arginine catabolism. Induction of all three enzymes is coordinate but is preceded by induction of the uptake system.