Study of purine degradation in aqueous solutions byParacoccus denitrificans

In this study the degradation of extracellular purines by the bacteriumParacoccus denitrificans was examined with aqueous purine solutions.Paracoccus denitrificans was able to decompose free purine bases and 5-mononucleotides. The nitrogen-containing products of the degradation were ammonia and urea. Purine uptake was the main control of purine decomposition. In the cases of guanine, xanthine, hypoxanthine, and urate, further control was exerted by induction. Furthermore, the uptake of the purines caused differences in the duration and temporal development of the substrate degration. It was also responsible for the inhibitory effects of the purines on the decomposition of one another when the substrates were used in mixtures. Also, fermentation parameters like biomass and purine concentration, pH, and temperature influenced the purine usage ofParacoccus denitrificans.     

Purine uptake by Alcaligenes eutrophus H16

The uptake of adenine, guanine, xanthine, hypoxanthine and uric acid by whole cells was studied, using spectrophotometric techniques, ¹⁴C-labelled compounds and metabolic inhibitors. Three different non-constitutive systems were shown to maintain the uptake of adenine and that of the pairs guanine/hypoxanthine and xanthine/uric acid. —Active transport of adenine was induced by adenine only, but passive uptake was also involved. Maximum K _T values of 110–131 M were observed at the pH optimum of 8.0. —Guanine and hypoxanthine were translocated by one single mechanism as indicated by K _T and K _I values. This system was induced by both these substances but its affinity was 51/2-times higher for guanine than for hypoxanthine; it was noncompetitively stimulated by Mg²⁺. — A further system, induced by xanthine and uric acid, catalyzed the uptake of both these compounds. It exhibited two pH optima (at pH 6.6 and 7.9); inactivation by heat and stimulation or inhibition by several compounds indicated that two separate mechanisms might be involved in the uptake of xanthine and uric acid.     

Purine requirements for the expression of Cape buffalo serum trypanocidal activity

Cape buffalo serum contains xanthine oxidase which generates trypanocidal H₂O₂ during the catabolism of hypoxanthine and xanthine. The present studies show that xanthine oxidase-dependent trypanocidal activity in Cape buffalo serum was also elicited by purine nucleotides, nucleosides, and bases even though xanthine oxidase did not catabolize those purines. The paradox was explained in part, by the presence in serum of purine nucleoside phosphorylase and adenosine deaminase, that, together with xanthine oxidase, catabolized adenosine, inosine, hypoxanthine, and xanthine to uric acid yielding trypanocidal H₂O₂. In addition, purine catabolism by trypanosomes provided substrates for serum xanthine oxidase and was implicated in the triggering of xanthine oxidase-dependent trypanocidal activity by purines that were not directly catabolized to uric acid in Cape buffalo serum, namely guanosine, guanine, adenine monophosphate, guanosine diphosphate, adenosine 3′:5-cyclic monophosphate, and 1-methylinosine. The concentrations of guanosine and guanine that elicited xanthine oxidase-dependent trypanocidal activity were 30–270-fold lower than those of other purines requiring trypanosome-processing which suggests differential processing by the parasites.     

Inhibition of purine utilization by adenine in Alcaligenes eutrophus H16

With 0.5% substrate present in mineral medium, cells of Alcaligenes eutrophus H 16 were able to grow heterotrophically at the expense of guanine, hypoxanthine and xanthine, but not of adenine as sole sources of carbon and nitrogen. An increase in cell counts, however, was observed at lower adenine concentrations (0.1%). Similarly, adenine was only respired if present at low concentrations. Higher amounts of adenine were inhibitory to the utilization of adenine, guanine, hypoxanthine, xanthine, allantoin and glyoxylate, but not to that of fructose or glycerate. The adenine-dependent inhibition of adenine utilization was not overcome by the addition of thiamine, uridine or cytidine. The enzyme glyoxylate carboligase, usually formed in presence of metabolisable purines and of allantoin, was synthesized only at low adenine concentrations. Higher amounts were inhibitory even with allantoin present as additional substrate. According to these resutls, the utilization of purine derivatives and of allantoin as sources of carbon and energy is repressed by adenine in cells of A. eutrophus H 16.     

Off‐host aggregation in the non‐fed,female brown dog tick,Rhipicephalus sanguineus (Latreille), is induced by tick excreta and enhanced by low relative humidity

We report that Rhipicephalus sanguineus (Ixodida: Ixodidae) faeces and its main component, guanine, act as assembly pheromones in short‐range Petri plate bioassays. Arrestment activity in response to guanine was lower than that in response to natural excreta, indicating the presence of other active ingredients in natural excreta. The selective removal of appendages was used to establish the important roles played by the palps and the front pair of legs in the detection of the pheromone. Reaction to chemically pure guanine at varying concentrations occurred without a dose response; thus only the presence of guanine, not a critical amount, is required to induce assembly. Higher speed and intensity of clustering occurred at 33% relative humidity (RH). We conclude that female adults of R. sanguineus are more prone to assemble under dry conditions that match the arid microhabitats preferred by this species and that this tendency allows this tick to reside in human dwellings and dog kennels that maintain standards of comfort at 30–50% RH. Cleaning or removing tick excreta‐covered surfaces on which ticks aggregate from within and around human dwellings may prove useful as a means of interfering with the establishment of off‐host clusters of R. sanguineus.     

Conversion of purines to xanthine by Methanococcus vannielii

Based on the finding that Methanococcus vannielii can employ any of several purines as the sole nitrogen source, an investigation was undertaken to elucidate the pathways of purine metabolism in this organism. Cell-free extracts of M. vannielii converted guanine, uric acid, and hypoxanthine to xanthine and also formed guanine from guanine nucleotides or guanosine. The conversions of guanine and uric acid to xanthine appear to occur by pathways similar to those described in clostridia. The conversion of hypoxanthine to xanthine, however, is different than that described for Clostridium cylindrosporum and C. acidiurici, but is similar to that of C. purinolyticum, and apparently involves the direct oxidation of hypoxanthine to xanthine.     

Transmission of Lyme disease spirochetes (Borrelia burgdorferi)

The field and laboratory evidence incriminating nymphalIxodes dammini as the main vectors ofBorrelia burgdorferi is substantial. Furthermore, other members of theIxodes (Ixodes) ricinus complex, includingI. ricinus, I. persulcatus, I. pacificus, andI. scapularis, are competent vectors of the Lyme disease spirochete. Although ticks in other genera are also naturally infected withB. burgdorferi, experimental evidence suggests thatAmblyomma andDermacentor ticks are inefficient vectors of these spirochetes. Current research on the kinetics ofB. burgdorferi growth within ticks demonstrates that Lyme disease spirochetes are dramatically influenced by physiological events during the tick's life-cycle.     

Distinction between Hypoxanthine and Xanthine Transport in Chlamydomonas reinhardtii

Chlamydomonas reinhardtii cells consumed hypoxanthine and xanthine by means of active systems which promoted purine intracellular accumulation against a high concentration gradient. Both uptake and accumulation were also observed in mutant strains lacking xanthine dehydrogenase activity. Xanthine and hypoxanthine uptake systems exhibited very similar Michaelis constants for transport and pH values, and both systems were induced by either hypoxanthine or xanthine. However, they differed greatly in the length of the lag phase before uptake induction, which was longer for hypoxanthine than for xanthine. Cells grown on ammonium and transferred to hypoxanthine media consumed xanthine before hypoxanthine, whereas cells transferred to xanthine media did not take up hypoxanthine until 2 hours after commencing xanthine consumption. Metabolic and photosynthetic inhibitors such as 2,4-dinitrophenol, 3-(3,4-dichlorophenyl)-1,1-dimethyl urea, and carbonylcyanide m-chlorophenylhydrazone inhibited to a different extent the hypoxanthine and xanthine uptake. Similarly, N-ethylmaleimide abolished xanthine uptake but slightly affected that of hypoxanthine. Hypoxanthine consumption was inhibited by adenine and guanine whereas that of xanthine was inhibited only by urate. We conclude that hypoxanthine and xanthine in C. reinhardtii are taken up by different active transport systems which work independently of the intracellular enzymatic oxidation of these purines.     

Peptostreptococcus barnesae sp. nov., a Gram-positive,anaerobic, obligately purine utilizing coccus from chicken feces

Anaerobic, Gram-positive cocci were obtained from chicken feces by direct isolation, which grew on the purines uric acid, xanthine, 6,8-dihydroxypurine, guanine, and hypoxanthine. Adenine and glycine were fermented, but not as readily. Acetate, formate, ammonia, and CO₂ were products. The isolated strains were nutritionally non-fastidious, however, they required selenite, molybdate, and tungstate as micronutrients. The cells were spherical and 0.5–0.9 m in diameter. The addition of bile salts enhanced the growth rate in most cases. The organisms proved to be quite resistant to lysis. The guanosine-plus-cytosine (G+C) content of their deoxyribonucleic acid was 33.6 to 34.8 mol%. The peptidoglycan was of the same structure (Gly-Lys-d-Asp) as reported for the anaerobic cocci of Hare group IX. However, the latter strains could only utilize glycine, not purines. Therefore, it is proposed to form a new species, Peptostreptococcus barnesae sp. nov.This paper is dedicated to Prof. Dr. Norbert Pfennig on the occasion of his 60th birthday     

Utilization of adenine and guanine as nitrogen sources by Chlamydomonas reinhardtii cells

Chlamydomonas reinhardtü Dangeard, adenine or guanine can be used as the sole nitrogen source for growth by means of an inducible system which is repressed by ammonia. Cells grown on either adenine or guanine were able to take up both purines, although the adenine uptake rate was always about 40% of the guanine uptake rate. Both adenine and guanine were taken up by an inducible system(s) exhibiting hyperbolic kinetics with identical apparent A, values of 3-2 mmol m^?3 for adenine and 3-2mmol m^?3 for guanine. Adenine and guanine utilization depended on pH, with similar optimal pH values of 7·3 and 7·4, respectively. Adenine and guanine each acted as a competitive inhibitor of the other's uptake, and their utilization was also inhibited by hypoxanthine, xanthine and urate. Inhibition of adenine uptake by guanine and hypoxanthine was competitive, with A′, values of 5·5 and 1. 6 mmol m^?3 respectively. Guanine uptake was also inhibited competitively by adenine (K₁= 1·3mmol m^?3) and hypoxanthine (K₁= 3. 3 mmol m^?3). Utilization of both adenine and guanine was inhibited by cyanide, azide, 3-(3,4-dichlorophenyl)-1,1-dimethyl urea, 2,4-dinitrophenol and carbonylcyanide m-chlorophenylhydrazone, and was also sensitive to p-hydroxymercuribenzoate and N-ethyl-maleimide. On the basis of these results, taken together, the possibility that adenine and guanine are translocated into Chlamydomonas by a common system is discussed.     

The substrate specificity of purine phosphoribosyltransferases in Schizosaccharomyces pombe

1. The activities of the purine phosphoribosyltransferases (EC 2.4.2.7 and 2.4.2.8) in purine-analogue-resistant mutants of Schizosaccharomyces pombe were checked. An 8-azathioxanthine-resistant mutant lacked hypoxanthine phosphoribosyltransferase, xanthine phosphoribosyltransferase and guanine phosphoribosyltransferase activities (EC 2.4.2.8) and appeared to carry a single mutation. Two 2,6-diaminopurine-resistant mutants retained these activities but lacked adenine phosphoribosyltransferase activity (EC 2.4.2.7). This evidence, together with data on purification and heat-inactivation patterns of phosphoribosyltransferase activities towards the various purines, strongly suggests that there are two phosphoribosyltransferase enzymes for purine bases in Schiz. pombe, one active with adenine, the other with hypoxanthine, xanthine and guanine. 2. Neither growth-medium supplements of purines nor mutations on genes involved in the pathway for new biosynthesis of purine have any influence on the amount of hypoxanthine-xanthine-guanine phosphoribosyltransferase produced by this organism.     

Control of induced infestations of three African multihost tick species with sustained-release ivermectin

The efficacy of ivermectin, released intraruminally from a 28-day-delivery device was evaluated in two titration studies against induced infestations of adultRhipicephalus appendiculatus, R. evertsi andHyalomma truncatum on cattle. Cattle were given a sufficient number of devices to release ivermectin at approximately 20, 40, 60 or 80 g kg^–1 day^–1 at a steady-state rate 7–28 days after administration. Tick mortality was recorded, engorged female ticks were weighed and individually incubated, and reproductive data were recorded to determine a reproductive index for the species at various dose levels. Mortality of male and female ticks compared to that of controls was directly related to the daily dose of ivermectin, as was the number of ticks not engorging. Ticks fed on ivermectin-treated cattle had a smaller mass when engorged and laid smaller egg-masses, both absolutely and as a proportion of engorged mass.The index of reproduction ofR. appendiculatus was reduced by more than 99.9% at 20 g kg^–1 day^–1, and the reproductive indices ofR. evertsi andH. truncatum were reduced by more than 99.9% at dose rates of 40 g kg^–1 day^–1 and above.Practical implications of the application of sustained-release ivermectin for the control of multihost ticks and tick-borne diseases are discussed.     

Pentatrichomonas hominis: purine salvage pathway

1. Pentatrichomonas hominis was found incapable of de novo synthesis of purines. 2. Pentatrichomonas hominis can salvage adenine, guanine, hypoxanthine, adenosine, guanosine and inosine, but not xanthine for the synthesis of nucleotides. 3. HPLC tracing of radiolabelled purines or purine nucleosides revealed that adenine, adenosine and hypoxanthine are incorporated into adenine nucleotides and IMP through a similar channel while guanine and guanosine are salvaged into guanine nucleotides via another route. There appears to be no direct interconversion between adenine and guanine nucleotides. Interconversion between AMP and IMP was observed. 4. Assays of purine salvage enzymes revealed that P. hominis possess adenosine kinase; adenosine, guanosine and inosine phosphotransferases; adenosine, guanosine and inosine phosphorylases and AMP deaminase.     

Absorption and metabolism of purines by the small intestine of the chicken.

1. Absorption of purines and their metabolism by the small intestine were estimated by using the everted gut sacs from the duodenum, jejunum and ileum of the chicken. 2. When no purine was added to the mucosal fluid, large amounts of uric acid, much less but appreciable adenine, hypoxanthine and xanthine and no detectable guanine were released from both sides of all segments of the small intestine, and these released amounts were largest in the duodenum. 3. Similar absorption rates of adenine from the jejunum and ileum were about 1.7-3.0 times as high as those of hypoxanthine and uric acid from these intestines and those of adenine and uric acid from the duodenum (P less than 0.05). 4. Guanine was not absorbed unchanged from any segments of the intestine and a little xanthine was absorbed only from the jejunum and ileum. 5. Guanine and xanthine seem to be absorbed in uric acid form, hypoxanthine in xanthine and uric acid forms and adenine in hypoxanthine form, from the small intestine especially from the jejunum. 6. Adenine, guanine, xanthine and hypoxanthine were greatly metabolized in the mucosa of the duodenum, and the conversions of hypoxanthine to xanthine and uric acid were most active.     

Absorption and metabolism of purines by the lower intestine of the chicken.

1. Absorption of purines and their metabolism by the lower intestine were estimated by using the everted gut sacs from the colo-rectum and caecum of the chicken. 2. Adenine, hypoxanthine and uric acid were appreciably absorbed from the colo-rectum and caecum, and an especially high rate was observed in the absorption of uric acid from the colo-rectum. 3. Guanine was not absorbed unchanged from either the colo-rectum or the caecum and a small amount of xanthine was absorbed only from the caecum. 4. Hypoxanthine was also absorbed in uric acid form, to a much lesser extent, in xanthine form from the colo-rectum and caecum, adenine and xanthine in uric acid form from the colo-rectum and adenine in hypoxanthine form from the colo-rectum and caecum. 5. Adenine was metabolized to hypoxanthine and xanthine, guanine and hypoxanthine to uric acid and xanthine, and xanthine to adenine, in both mucosal fluids of the colo-rectum and caecum. The conversion of guanine to uric acid in the caecum was most active, being almost twice as much as that in the colo-rectum.     

Purine-Excretory Nature of Refractile Bodies in the Marine Ciliate Parauronema acutum*

SYNOPSIS. A method was developed for the isolation and purification of crystalline, highly refractile bodies found in the cytoplasm of a symbiote-free strain of the marine hymenostome ciliate, Parauronema acutum, strain 110–3. Chemical analysis of the purified refractile bodies revealed an abundance of the purines, hypoxanthine and guanine. It was evident from studies involving the use of ¹⁴C-labeled precursors that both hypoxanthine and guanine are derived from higher purine derivatives. We postulate that these bodies are excretory in function and that guanine and hypoxanthine are major endproducts of purine metabolism of P. acutum.     

A comparison of purine metabolism and nucleotide pools in normal and hypoxanthine-guanine phosphoribosyltransferase-deficient neuroblastoma cells

Purine nucleotide synthesis and interconversion were examined over a range of purine base and nucleoside concentrations in intact N4 and N4TG (hypoxanthine-guanine phosphoribosyltransferase (HGPRT) deficient) neuroblastoma cells. Adenosine was a better nucleotide precursor than adenine, hypoxanthine or guanine at concentrations greater than 100 μM. With hypoxanthine or guanine, N4TG cells had less than 2% the rate of nucleotide synthesis of N4 cells. At substrate concentrations greater than 100 μM the rates for deamination of adenosine and phosphorolysis of guanosine exceeded those for any reaction of nucleotide synthesis. Labelled inosine and guanosine accumulated from hypoxanthine and guanine, respectively, in HGPRT-deficient cells and the nucleosides accumulated to a greater extent in N4 cells indicating dephosphorylation of newly synthesized IMP and GMP to be quantitatively significant. A deficiency of xanthine oxidase, guanine deaminase and guanosine kinase activities was found in neuroblastoma cells. Hypoxanthine was a source for both adenine and guanine nucleotides, whereas adenine or guanine were principally sources for adenine (>85%) or guanine (>90%) nucleotides, respectively. The rate of [¹⁴C]formate incorporation into ATP, GTP and nucleic acid purines was essentially equivalent for both N4 and N4TG cells. Purine nucleotide pools were also comparable in both cell lines, but the concentration of UDP-sugars was 1.5 times greater in N4TG than N4 cells.     

Purine Utilization by Klebsiella oxytoca M5al: Genes for Ring-Oxidizing and -Opening Enzymes

The enterobacterium Klebsiella oxytoca uses a variety of inorganic and organic nitrogen sources, including purines, nitrogen-rich compounds that are widespread in the biosphere. We have identified a 23-gene cluster that encodes the enzymes for utilizing purines as the sole nitrogen source. Growth and complementation tests with insertion mutants, combined with sequence comparisons, reveal functions for the products of these genes. Here, we report our characterization of 12 genes, one encoding guanine deaminase and the others encoding enzymes for converting (hypo)xanthine to allantoate. Conventionally, xanthine dehydrogenase, a broadly distributed molybdoflavoenzyme, catalyzes sequential hydroxylation reactions to convert hypoxanthine via xanthine to urate. Our results show that these reactions in K. oxytoca are catalyzed by a two-component oxygenase (HpxE-HpxD enzyme) homologous to Rieske nonheme iron aromatic-ring-hydroxylating systems, such as phthalate dioxygenase. Our results also reveal previously undescribed enzymes involved in urate oxidation to allantoin, catalyzed by a flavoprotein monooxygenase (HpxO enzyme), and in allantoin conversion to allantoate, which involves allantoin racemase (HpxA enzyme). The pathway also includes the recently described PuuE allantoinase (HpxB enzyme). The HpxE-HpxD and HpxO enzymes were discovered independently by de la Riva et al. (L. de la Riva, J. Badia, J. Aguilar, R. A. Bender, and L. Baldoma, J. Bacteriol. 190:7892-7903, 2008). Thus, several enzymes in this K. oxytoca purine utilization pathway differ from those in other microorganisms. Isofunctional homologs of these enzymes apparently are encoded by other species, including Acinetobacter, Burkholderia, Pseudomonas, Saccharomyces, and Xanthomonas.Purines and purine derivatives comprise a large portion of biomass and are involved in almost every step of life. Not only a major constituent of nucleic acids, they also are central to energy transfer and storage (ATP) as well as protein synthesis and signaling (GTP). Plants, animals, and many microorganisms use purines and purine derivatives to store and translocate nitrogen for assimilation or excretion (96).Salvage pathways operate to recycle purines, including hypoxanthine and xanthine, back into nucleoside pools (107). Additionally, some organisms can utilize purines as the sole source of nitrogen and carbon. Adenine and guanine are deaminated to form hypoxanthine and xanthine, respectively, which then are oxidized to form uric acid (urate at physiological pH) (Fig. ​(Fig.1).1). These oxidation steps are catalyzed by xanthine dehydrogenase, a well-studied molybdoflavoenzyme that is conserved from bacteria to humans (51). Two sequential ring-opening steps convert urate via allantoin to allantoate (Fig. ​(Fig.1).1). Subsequent steps, which comprise different pathways in different microorganisms (96), convert allantoate to ammonium, which is assimilated.Open in a separate windowFIG. 1.Purine ring oxidation and opening steps. The enzyme proposed to catalyze each step is shown. The K. oxytoca gene for adenine deaminase was not identified in this study. Dashed lines show reactions that can occur spontaneously.Some organisms express only the latter portion of the purine utilization pathway and cannot use purines or urate as sole sources of nitrogen. For example, Escherichia coli K-12 can use allantoin and its catabolites as the sole nitrogen source, albeit only under anaerobic conditions (21). Saccharomyces cerevisiae uses allantoin as a nitrogen storage compound (17). However, the complete pathway is present in other bacterial and fungal species, including Bacillus subtilis (84) and Aspergillus nidulans (83).Molybdoenzymes (excepting dinitrogenase) contain the molybdenum cofactor Mo-molybdopterin (42). Thus, mutations in genes for molybdenum cofactor biosynthetic enzymes (mol genes in bacteria and cnx in A. nidulans) confer pleiotropic phenotypes: these mutants can utilize neither nitrate nor purines, due to lack of the molybdoenzymes nitrate reductase and xanthine dehydrogenase (74). We previously reported that Klebsiella oxytoca mol mutants cannot assimilate nitrate but can utilize xanthine as the sole nitrogen source (32). This suggested, as one possibility, that K. oxytoca uses a molybdenum-independent enzyme in place of conventional xanthine dehydrogenase. Results reported here demonstrate that this is correct, as insertion mutants blocked specifically in xanthine and hypoxanthine utilization define the structural genes for an apparent two-component Reiske nonheme iron oxygenase.Here, we report analysis of 12 genes whose products catalyze conversion of purines to allantoate. Our investigation of the remaining genes, whose products catalyze allantoate utilization, is ongoing. Results show that several steps in the overall pathway are catalyzed by previously undescribed enzymes.While this paper was in review, the paper by de la Riva et al. (24), describing the hpxDE, hpxR, hpxO, and hpxPQT genes from Klebsiella pneumoniae W70, was posted in the “JB Accepts” section of the Journal of Bacteriology online edition. Results and conclusions concerning these seven genes are congruent between the two studies.(Some of the work presented here was submitted by Danielle Carl in 1994 as part of an undergraduate thesis to the Cornell University Division of Biological Sciences Honors Program.)     

Effects of chronic allopurinol therapy on purine metabolism in Duchenne muscular dystrophy

Adenine, adenosine, inosine, hypoxanthine, xanthosine, xanthine, guanine and guanosine blood levels in 11 Duchenne muscular dystrophy patients treated with allopurinol, 10 untreated patients and 8 healthy controls, were determined by HPLC. Serum ADA, PNP and 5'-NT were also determined. Untreated patients showed lower adenine (p less than 0.001) and higher adenosine, xanthine, ADA and PNP levels (p less than 0.01) than controls. Treated patients had lower adenine and higher xanthine levels (p less than 0.001), but higher hypoxanthine, xanthosine and guanine levels (p less than 0.001), than controls, with normal ADA and PNP. The changes observed in ADA and PNP levels suggest an involvement of these enzymes in accelerated degradation of purines in Duchenne dystrophy.     

The seabird tick, <Emphasis Type="Italic">Ixodes</Emphasis><Emphasis Type="Italic">uriae</Emphasis>, uses uric acid in penguin guano as a kairomone and guanine in tick feces as an assembly pheromone on the Antarctic Peninsula

In the vicinity of Palmer Station, Antarctica, the seabird tick, Ixodes uriae, forms large aggregations under rocks at the periphery of Adelie penguin rookeries. When the adult penguins return to the rookeries at the beginning of the nesting season the ticks leave their off-host aggregation site, attach to the penguins for a period of feeding, and then subsequently return to the aggregation site. In this study, we searched for chemical cues that may be used by the ticks to locate their aggregation sites as well as cues involved in finding penguins. Tick excreta and soil extracts from beneath tick aggregations contained a pheromone that elicited assembly behavior in unfed larvae, non-fed nymphs and non-fed adults. Guanine, the major excretory product of ticks, elicited assembly behavior, thus, guanine is likely an active component involved in assembly. Non-fed stages also responded positively to penguin guano and uric acid, the primary excretory product of penguins, suggesting that uric acid and other components of penguin guano function as a kairomone used by the non-fed ticks to locate their host. After feeding, the immature ticks’ response to both the assembly and kairomones is switched off for several days, and the ticks regain responsiveness only after they have molted. Fed adult females lay eggs and die without ever regaining responsiveness. Thus, I. uriae relies on two closely related chemicals to regulate two critical aspects of its life: assembly and host-finding. Guanine and other components of tick excreta function as an assembly pheromone in promoting the formation of off-host aggregations, while uric acid and other components of penguin guano function as a kairomone used by the tick to locate its host.