Stimulated transport of hypoxanthine in Crithidia luciliae: relationship to purine stress

Parasitology ◽  
1997 ◽  
Vol 114 (1) ◽  
pp. 19-27 ◽  
Author(s):  
R. E. DAY ◽  
A. M. GERO
Keyword(s):  
Substrate Specificity ◽  
Transport System ◽  
Diffusion System ◽  
Purine Nucleoside ◽  
Transport Mechanisms ◽  
Nucleotidase Activity ◽  
Purine Salvage ◽  
Purine Bases ◽  
Crithidia Luciliae ◽  
Adenosine Transport

Hypoxanthine transport in the insect trypanosome, Crithidia luciliae, was activated in purine depleted conditions. The existence of 2 hypoxanthine transport mechanisms was established. The first, a non-saturable diffusion system, present in purine replete conditions, exhibited properties that were different from the second transport system which was evident only during purine depleted conditions (purine stress). The rate of transport under purine stress was elevated approximately 8-fold over that in replete conditions. This transporter was saturable with a Km of 3·9 μM for hypoxanthine. The transporter substrate specificity included other purine bases, e.g. adenine and guanine, and the purine nucleoside, adenosine. These inhibited hypoxanthine transport competitively with Ki values of 2 μM, 3 μM and 42 μM respectively. Coincident with the increase of hypoxanthine transport under purine stress, the transport of adenosine increased 4-fold and the activity of the 3′-nucleotidase ectoenzyme also increased significantly. Under purine stress the concurrent increase of hypoxanthine and adenosine transport and the increase in 3′-nucleotidase activity could be repressed with either the supplementation of excess purines or by cycloheximide. This study of purine salvage mechanisms in Crithidia luciliae illustrates the successful adaptation of the parasite to nutritional insufficiency.

scholarly journals Substrate specificity of the purine-2′-deoxyribonucleosidase of Crithidia luciliae

1992 ◽  
Vol 287 (1) ◽  
pp. 125-129 ◽  
Author(s):  
D J Steenkamp ◽  
T J F Hälbich
Keyword(s):  
Substrate Specificity ◽  
The Other ◽  
Methyl Groups ◽  
Michaelis Constant ◽  
Purine Analogues ◽  
Purine Bases ◽  
Crithidia Luciliae ◽  
Other Hand

The purine-2′-deoxyribonucleosidase of Crithidia luciliae catalyses an efficient deoxyribosyl transfer between a variety of purine bases, benzimidazole and 5,6-dimethylbenzimidazole. Since the deoxyriboside of a deoxyribosyl acceptor is necessarily also a substrate, the trans-N-deoxyribosylase activity of the enzyme allows a study of its specificity to be extended to a large number of purines and purine analogues. Amongst 27 different deoxyribosyl acceptors, only hypoxanthine gave rise to isomeric products. The introduction of methyl groups at appropriate positions in either purine or benzimidazole lowered the Michaelis constant, KB, for deoxyribosyl acceptors: by about 10-fold for 6-methylpurine (KB 351 +/- 87 microM) compared with purine (KB 3.91 +/- 0.8 mM) and by about 10(3)-fold for 5,6-dimethylbenzimidazole (KB 7.0 +/- 0.79 microM) compared with benzimidazole (Km,app. 7.8 +/- 2.4 mM). The maximal rates of deoxyribosyl transfer to different acceptors, on the other hand, varied by only 4.5-fold, and can be ascribed to decreases in the rate of release of the newly formed purine deoxyriboside from the enzyme.

scholarly journals Characteristics of bile salt uptake into skate hepatocytes

1994 ◽  
Vol 299 (3) ◽  
pp. 665-670 ◽  
Author(s):  
G Fricker ◽  
V Dubost ◽  
K Finsterwald ◽  
J L Boyer
Keyword(s):  
Substrate Specificity ◽  
Bile Salt ◽  
Transport System ◽  
Bile Salts ◽  
Organic Anion ◽  
Anion Transport ◽  
Organic Anion Transport ◽  
Salt Uptake ◽  
Anion Transport System ◽  
Alpha 7

The substrate specificity for the transporter that mediates the hepatic uptake of organic anions in freshly isolated hepatocytes of the elasmobranch little skate (Raja erinacea) was determined for bile salts and bile alcohols. The Na(+)-independent transport system exhibits a substrate specificity, which is different from the specificity of Na(+)-dependent bile salt transport in mammals. Unconjugated and conjugated di- and tri-hydroxylated bile salts inhibit uptake of cholyltaurine and cholate competitively. Inhibition is significantly greater with unconjugated as opposed to glycine- or taurine-conjugated bile salts. However, the number of hydroxyl groups in the steroid moiety of the bile salts has only minor influences on the inhibition by the unconjugated bile salts. Since the transport system seems to represent an archaic organic-anion transport system, other anions, such as dicarboxylates, amino acids and sulphate, were also tested, but had no inhibitory effect on bile salt uptake. To clarify whether bile alcohols, the physiological solutes in skate bile, share this transport system, cholyltaurine transport was studied after addition of 5 beta-cholestane-3 beta,5 alpha,6 beta-triol, 5 alpha-cholestan-3 beta-ol and 5 beta-cholestane-3 alpha, 7 alpha, 12 alpha-triol. These bile alcohols inhibit cholyltaurine uptake non-competitively. In contrast, uptake of 5 beta-cholestane-3 alpha,7 alpha,12 alpha-triol, which is Na(+)-independent, is not inhibited by cholyltaurine. The findings further characterize a Na(+)-independent organic-anion transport system in skate liver cells, which is not shared by bile alcohols and has preference for unconjugated lipophilic bile salts.

scholarly journals Purine nucleoside phosphorylase in chronic lymphocytic leukemia (CLL)

Blood ◽  
1978 ◽  
Vol 52 (5) ◽  
pp. 886-895 ◽  
Author(s):  
M Borgers ◽  
H Verhaegen ◽  
M De Brabander ◽  
J De Cree ◽  
W De Cock ◽  
...  
Keyword(s):  
Chronic Lymphocytic Leukemia ◽  
Healthy Subjects ◽  
Purine Nucleoside Phosphorylase ◽  
Peripheral Blood Lymphocytes ◽  
Lymphocytic Leukemia ◽  
Purine Nucleoside ◽  
Salvage Pathway ◽  
Purine Salvage ◽  
Nucleoside Phosphorylase ◽  
A Minor

Abstract Purine nucleoside phosphorylase (PNP), the enzyme schematically next to adenosine deaminase in the purine salvage pathway, has been demonstrated cytochemically in peripheral blood lymphocytes of healthy subjects and chronic lymphocytic leukemia (CLL) patients. The enzyme activity is confined to the cytosol. In healthy subjects the majority of lymphocytes are strongly reactive for PNP, whereas the rest are devoid of cytochemically demonstrable activity. The percentage of PNP- positive cells largely corresponds to the number of E rosette-forming cells and is inversely proportional to the number of Ig-bearing cells. In six of seven CLL patients studied only a minor percentage of the lymphocytes showed strong PNP activity, whereas the large majority (88%- -98%) possessed trace activity. Such patients have a high number of Ig- bearing cells and a low number of E rosette-forming cells. A different pattern of markers was found in the lymphocytes of the seventh CLL patient: 66% were strongly reactive for PNP, an important number formed E rosettes, and a minor percentage were Ig bearing. These data indicate that PNP can be useful as a “nonmembrane” marker in the differentiation of the B and T cell origin in CLL and deserves to be studied in other lymphoproliferative disorders.

Specificity of Milk Peptide Utilization byLactococcus lactis

1998 ◽  
Vol 64 (4) ◽  
pp. 1230-1236 ◽  
Author(s):  
Vincent Juillard ◽  
Alain Guillot ◽  
Dominique Le Bars ◽  
Jean-Claude Gripon
Keyword(s):  
Substrate Specificity ◽  
Transport System ◽  
Time Course ◽  
Solid Phase ◽  
Amino Acid Content ◽  
Defined Medium ◽  
Milk Peptides ◽  
Basic Peptides ◽  
Oligopeptide Transport System ◽  
Oligopeptide Transport

ABSTRACT To study the substrate specificity of the oligopeptide transport system of Lactococcus lactis for its natural substrates, the growth of L. lactis MG1363 was studied in a chemically defined medium containing milk peptides or a tryptic digest of αs2-casein as the source of amino acids. Peptides were separated into acidic, neutral, and basic pools by solid-phase extraction or by cation-exchange liquid chromatography. Their ability to sustain growth and the time course of their utilization demonstrated the preferential use of hydrophobic basic peptides with molecular masses ranging between 600 and 1,100 Da by L. lactis MG1363 and the inability to use large, acidic peptides. These peptide utilization preferences reflect the substrate specificity of the oligopeptide transport system of the strain, since no significant cell lysis was inferred. Considering the free amino acid content of milk and these findings on peptide utilization, it was demonstrated that the cessation of growth of L. lactis MG1363 in milk was due to deprivation of leucine and methionine.

scholarly journals Properties of the canalicular bile acid transport system in rat liver

1987 ◽  
Vol 242 (2) ◽  
pp. 465-469 ◽  
Author(s):  
P J Meier ◽  
A S Meier-Abt ◽  
J L Boyer
Keyword(s):  
Bile Acid ◽  
Substrate Specificity ◽  
Bile Acids ◽  
Rat Liver ◽  
Transport System ◽  
Acid Transport ◽  
Bile Acid Transport ◽  
Canalicular Bile ◽  
Disulphonic Acid ◽  
Bile Acid Carrier

4,4-Di-isothiocyanostilbene-2,2′-disulphonic acid inhibition of taurocholate efflux from canalicular vesicles was used to demonstrate that potential driven and ‘carrier’-mediated canalicular excretion of taurocholate occur via a common, rather than two separate, pathways. This electrogenic canalicular bile acid ‘carrier ’ preferentially transports trihydroxylated and conjugated dihydroxylated bile acids, but not the unphysiological oxo bile acids, and possibly extends its substrate specificity to other amphipathic molecules such as sulphobromophthalein.

scholarly journals Formycin A Resistant Mutants Due to Defect in Adenosine Transport System in Vibrio parahaemolyticus.

1991 ◽  
Vol 39 (5) ◽  
pp. 1325-1327 ◽  
Author(s):  
Yuki SAKAI-TOMITA ◽  
Yuki MITANI ◽  
Masaaki TSUDA ◽  
Tomofusa TSUCHIYA
Keyword(s):  
Transport System ◽  
Vibrio Parahaemolyticus ◽  
Adenosine Transport ◽  
Resistant Mutants

Identification of a novel putative inhibitor of the Plasmodium falciparum purine nucleoside phosphorylase: exploring the purine salvage pathway to design new antimalarial drugs

2017 ◽  
Vol 21 (3) ◽  
pp. 677-695 ◽  
Author(s):  
Luciano Porto Kagami ◽  
Gustavo Machado das Neves ◽  
Ricardo Pereira Rodrigues ◽  
Vinicius Barreto da Silva ◽  
Vera Lucia Eifler-Lima ◽  
...  
Keyword(s):  
Plasmodium Falciparum ◽  
Purine Nucleoside Phosphorylase ◽  
Antimalarial Drugs ◽  
Purine Nucleoside ◽  
Salvage Pathway ◽  
Purine Salvage ◽  
Nucleoside Phosphorylase
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