Platypus Research Articles

Thermal fluctuations of haemoglobin from different species: adaptation to temperature via conformational dynamics

Thermodynamic stability, configurational motions and internal forces of haemoglobin (Hb) of three endotherms (platypus, Ornithorhynchus anatinus; domestic chicken, Gallus gallus domesticus and human, Homo sapiens) and an ectotherm (salt water crocodile, Crocodylus porosus) were investigated using circular dichroism, incoherent elastic neutron scattering and coarse-grained Brownian dynamics simulations. The experimental results from Hb solutions revealed a direct correlation between protein resilience, melting temperature and average body temperature of the different species on the 0.1 ns time scale. Molecular forces appeared to be adapted to permit conformational fluctuations with a root mean square displacement close to 1.2 Å at the corresponding average body temperature of the endotherms. Strong forces within crocodile Hb maintain the amplitudes of motion within a narrow limit over the entire temperature range in which the animal lives. In fully hydrated powder samples of human and chicken, Hb mean square displacements and effective force constants on the 1 ns time scale showed no differences over the whole temperature range from 10 to 300 K, in contrast to the solution case. A complementary result of the study, therefore, is that one hydration layer is not sufficient to activate all conformational fluctuations of Hb in the pico- to nanosecond time scale which might be relevant for biological function. Coarse-grained Brownian dynamics simulations permitted to explore residue-specific effects. They indicated that temperature sensing of human and chicken Hb occurs mainly at residues lining internal cavities in the β-subunits.

A Model for the Evolution of the Mammalian T-cell Receptor / and Loci Based on Evidence from the Duckbill Platypus

The specific recognition of antigen by T cells is critical to the generation of adaptive immune responses in vertebrates. T cells recognize antigen using a somatically diversified T-cell receptor (TCR). All jawed vertebrates use four TCR chains called α, β, γ, and δ, which are expressed as either a αβ or γδ heterodimer. Nonplacental mammals (monotremes and marsupials) are unusual in that their genomes encode a fifth TCR chain, called TCRµ, whose function is not known but is also somatically diversified like the conventional chains. The origins of TCRµ are also unclear, although it appears distantly related to TCRδ. Recent analysis of avian and amphibian genomes has provided insight into a model for understanding the evolution of the TCRδ genes in tetrapods that was not evident from humans, mice, or other commonly studied placental (eutherian) mammals. An analysis of the genes encoding the TCRδ chains in the duckbill platypus revealed the presence of a highly divergent variable (V) gene, indistinguishable from immunoglobulin heavy (IgH) chain V genes (VH) and related to V genes used in TCRµ. They are expressed as part of TCRδ repertoire (VHδ) and similar to what has been found in frogs and birds. This, however, is the first time a VHδ has been found in a mammal and provides a critical link in reconstructing the evolutionary history of TCRµ. The current structure of TCRδ and TCRµ genes in tetrapods suggests ancient and possibly recurring translocations of gene segments between the IgH and TCRδ genes, as well as translocations of TCRδ genes out of the TCRα/δ locus early in mammals, creating the TCRµ locus.

Diversity at the Major Histocompatibility Complex Class II in the Platypus, Ornithorhynchus anatinus

The platypus (Ornithorhynchus anatinus) is the sole survivor of a previously widely distributed and diverse lineage of ornithorhynchid monotremes. Its dependence on healthy water systems imposes an inherent sensitivity to habitat degradation and climate change. Here, we compare genetic diversity at the major histocompatibility complex (MHC) Class II-DZB gene and 3 MHC-associated microsatellite markers with diversity at 6 neutral microsatellite markers in 70 platypuses from across their range, including the mainland of Australia and the isolated populations of Tasmania, King Island, and Kangaroo Island. Overall, high DZB diversity was observed in the platypus, with 57 DZB β1 alleles characterized. Significant positive selection was detected within the DZB peptide-binding region, promoting variation in this domain. Low levels of genetic diversity were detected at all markers in the 2 island populations, King Island (endemic) and Kangaroo Island (introduced), with the King Island platypuses monomorphic at the DZB locus. Loss of MHC diversity on King Island is of concern, as the population may have compromised immunological fitness and reduced ability to resist changing environmental conditions.

Bioorganic studies on the venom from duckbill platypus

Venomous mammals are rare, and only a few species in the orders Insectivora and Monotremata produce toxic venom. Among them, the duckbill platypus (Ornithorhynchus anatinus) is one of the two venomous Australian mammals. The adult male platypus carries a spur on each hind leg, which it uses to inject competitors with poison. However, the structure and function of the poison’s active compounds are still imcompletely characterized. We found that crude platypus venom produced potent Ca2+influx in human neuroblastoma IMR-32 cells. Guided by this assay, we identified 11 unique peptides, including peptide H–His–Asp–His–Pro–Asn–Pro–Arg–OH, which coincided with the N-terminal domain residues ofOrnithorhynchusvenom C-type natriuretic peptide (OvCNP). This heptapeptide induced a significant increase in [Ca2+]iin IMR-32 cells at 75 μM; had relatively specific affinities for glutamate, histamine, and GABAAreceptors; and facilitated neurogenic twitching in guinea pig ileum specimens at 30 μM. We also established that its proteinous venom fraction strongly hydrolyzed Pro–Phe–Arg–MCA and cleaved a human low-molecular-weight kininogen (LK), similar to porcine pancreas kallikrein. These results strongly indicated that platypus venom contains tissue kallikrein-like protease(s), and its proteolytic activity might synergistically contribute to toxicity through the specific cleavage of other venom constituents.

ACP5 (Uteroferrin): Phylogeny of an Ancient and Conserved Gene Expressed in the Endometrium of Mammals1

Type 5 acid phosphatase (ACP5; also known as tartrate-resistant acid phosphatase or uteroferrin) is a metalloprotein secreted by the endometrial glandular epithelium of pigs, mares, sheep, and water buffalo. In this paper, we describe the phylogenetic distribution of endometrial expression of ACP5 and demonstrate that endometrial expression arose early in evolution (i.e., before divergence of prototherian and therian mammals ~166 million years ago). To determine expression of ACP5 in the pregnant endometrium, RNA was isolated from rhesus, mouse, rat, dog, sheep, cow, horse, armadillo, opossum, and duck-billed platypus. Results from RT-PCR and RNA-Seq experiments confirmed that ACP5 is expressed in all species examined. ACP5 was also demonstrated immunochemically in endometrium of rhesus, marmoset, sheep, cow, goat, and opossum. Alignment of inferred amino acid sequences shows a high conservation of ACP5 throughout speciation, with species-specific differences most extensive in the N-terminal and C-terminal regions of the protein. Analysis by Selecton indicated that most of the sites in ACP5 are undergoing purifying selection, and no sites undergoing positive selection were found. In conclusion, endometrial expression of ACP5 is a common feature in all orders of mammals and has been subjected to purifying selection. Expression of ACP5 in the uterus predates the divergence of therians and prototherians. ACP5 is an evolutionary conserved gene that likely exerts a common function important for pregnancy in mammals using a wide range of reproductive strategies.

Small population size and extremely low levels of genetic diversity in island populations of the platypus, Ornithorhynchus anatinus.

Genetic diversity generally underpins population resilience and persistence. Reductions in population size and absence of gene flow can lead to reductions in genetic diversity, reproductive fitness, and a limited ability to adapt to environmental change increasing the risk of extinction. Island populations are typically small and isolated, and as a result, inbreeding and reduced genetic diversity elevate their extinction risk. Two island populations of the platypus, Ornithorhynchus anatinus, exist; a naturally occurring population on King Island in Bass Strait and a recently introduced population on Kangaroo Island off the coast of South Australia. Here we assessed the genetic diversity within these two island populations and contrasted these patterns with genetic diversity estimates in areas from which the populations are likely to have been founded. On Kangaroo Island, we also modeled live capture data to determine estimates of population size. Levels of genetic diversity in King Island platypuses are perilously low, with eight of 13 microsatellite loci fixed, likely reflecting their small population size and prolonged isolation. Estimates of heterozygosity detected by microsatellites (HE= 0.032) are among the lowest level of genetic diversity recorded by this method in a naturally outbreeding vertebrate population. In contrast, estimates of genetic diversity on Kangaroo Island are somewhat higher. However, estimates of small population size and the limited founders combined with genetic isolation are likely to lead to further losses of genetic diversity through time for the Kangaroo Island platypus population. Implications for the future of these and similarly isolated or genetically depauperate populations are discussed.

Evidence for an endogenous papillomavirus-like element in the platypus genome

Papillomaviruses (PVs) infect a wide range of vertebrates and have diversified into multiple genetic types, some of which have serious consequences for human health. Although PVs have to date only been characterized as exogenous viral forms, here we report the observation of an endogenous viral element (EPVLoa) in the genome of the platypus (Ornithorhynchus anatinus) that is related to PVs. Further data mining for endogenous PV-like elements is therefore warranted.

Platypus TCRμ Provides Insight into the Origins and Evolution of a Uniquely Mammalian TCR Locus

TCRμ is an unconventional TCR that was first discovered in marsupials and appears to be absent from placental mammals and nonmammals. In this study, we show that TCRμ is also present in the duckbill platypus, an egg-laying monotreme, consistent with TCRμ being ancient and present in the last common ancestor of all extant mammals. As in marsupials, platypus TCRμ is expressed in a form containing double V domains. These V domains more closely resemble Ab V than that of conventional TCR. Platypus TCRμ differs from its marsupial homolog by requiring two rounds of somatic DNA recombination to assemble both V exons and has a genomic organization resembling the likely ancestral form of the receptor genes. These results demonstrate that the ancestors of placental mammals would have had TCRμ but it has been lost from this lineage.

Effect of sex and age on temporal variation in the frequency and direction of platypus (Ornithorhynchus anatinus) captures in fyke nets

Fyke netting is currently the method mainly used to describe the demographic attributes of platypus (Ornithorhynchus anatinus) populations occupying relatively shallow, flowing water bodies. Based on fieldwork carried out in Victoria from 1995 to 2010, fyke netting surveys conducted in the month when the highest frequency of nightly captures was recorded (July) resulted in nearly three times as many adults and subadults entering nets as compared with those scheduled in the months when the fewest nightly captures were recorded (April and May). Significant sex-specific variation was apparent in relation to monthly capture frequencies: males were captured most often in August (the start of the breeding season), whereas females were captured most often in January (the peak period of lactation). The frequency of platypus captures also varied significantly when considered on a nocturnal time scale, with 63% of adult and subadult captures and 73% of juvenile captures being recorded in the first half of the night. Both juveniles (<11 months) and older animals also showed a significant tendency to travel upstream in the first half of the night. These potential sources of bias in datasets need to be considered when analysing and comparing the results of platypus fyke netting studies.

The Prime Minister and the platypus: A paradox goes to war

In February 1943, in the midst of the Second World War, Prime Minister Winston Churchill demanded that a live duck-billed platypus be sent from Australia to Britain. A vigorous male was shipped off but died shortly before arrival in Britain. This request can only be understood if placed in the context of Churchill’s passion for exotic pets as well as the rich history of aristocratic menageries and live diplomatic gifts. Obtaining an animal hitherto unseen alive in Europe would have been a great zoological achievement for London Zoo and secured British authority in heated historical taxonomical debates. This zoological triumph, coupled with accomplishing an extravagant enterprise in the middle of war-time austerity would have boosted public morale. Most importantly, despite its death, the platypus, served as a token for mediating the soured relations between Australia and Britain. Churchill’s platypus provides a unique case of animal collecting that incorporates effects on international diplomacy and public relations along with a great private eccentricity and passion.

Genetic structure and phylogeography of platypuses revealed by mitochondrial DNA

AbstractThe platypus Ornithorhynchus anatinus is an endemic monotreme species with a wide latitudinal distribution in eastern Australia, including Tasmania. Understanding of the phylogeography within this species is very limited at present and represents a gap in the documentation of Australia's unique biodiversity. We analysed mitochondrial DNA sequences (partial control region and complete cytochrome b, including portions of flanking tRNAs) of 74 individuals from across the distribution of the species. Phylogenetic analysis of the concatenated sequences corroborated the primary split within the platypus, showing two major clades: one from mainland Australia and the other from Tasmania/King Island. Estimates of divergence times suggest that these clades last shared a common mitochondrial ancestor ∼0.7–0.94 Ma. Using an extended dataset of partial control region sequences from 284 individuals, we found evidence of genetic structure between river basins, primarily within mainland Australia, as well as an additional divergent lineage in North‐eastern Australia. Overall, few haplotypes were shared between river basins. Analyses of molecular variance of the control region sequences indicated low rates of gene flow and significant divergence, particularly at the river basin and geographical area scales.

Early response of the platypus to climate warming

AbstractCombining a climatic envelope modelling technique with more than two centuries (1800–2009) of distribution records has revealed the effects of a changing climate on the egg‐laying monotreme, the platypus, Ornithorhynchus anatinus. We show that the main factor associated with platypus occurrence switched from aquatic habitat availability (estimated by rainfall) to thermal tolerances (estimated by annual maximum temperature) in the 1960s. This correlates directly with the change in the annual maximum temperature anomaly from cooler to warmer conditions in southeastern Australia. Modelling of platypus habitat under emission scenarios (A1B, A2, B1 and B2) revealed large decreases (>30%) in thermally suitable habitat by 2070. This reduction, compounded by increasing demands for water for agriculture and potable use, suggests that there is real cause for concern over the future status of this species, and highlights the need for restoration of thermal refugia within the platypus’ modelled range.

Infrasound in the flutter-jump display of Capercaillie (Tetrao urogallus): signal or artefact?

The perceptual world of non-human animals has long been recognized as differing markedly from that of humans (von Uexkull 1909). Selection has favoured animal responsiveness to stimuli outside the perceptual range of humans in the mechanical (Sorex palustris, Catania et al. 2008; Schizocosa spp., Uetz et al. 2009), chemical (Felis catus, De Boer 1977), electrical (Scyliorhinus canicula and Raja clavata, Kalmijn 1971; Polyodon spathula and Ornithorhyncus anatinus, Pettigrew and Wilkens 2003), magnetic (birds, Mouritsen and Ritz 2005), thermal (Boidae and Crotalinae, Ebert et al. 2007), and acoustic (echolocation in bats, Simmons 1973; ultrasound in ground squirrels, Wilson and Hare 2004; ultrasound in toothed whales, Wilson et al. 2007) domains. In addition to the utilization of sounds beyond the upper frequency limit of human hearing ([15 kHz: ultrasound), elephants (Elephas maximus, Payne et al. 1986), rhinos (Diceros bicornis spp., Budde and Klump 2003), giraffes (Giraffe camelonardalis reticulata, von Muggenthaler et al. 1999), and whales (Balaenoptera physalus, Payne and Webb 1971) communicate using frequencies below the lower frequency limit of human hearing (\20 Hz: infrasound). Several bird species produce infrasound. Capercaillie (Tetrao urogallus) produce infrasound in their flutter-jump displays (Lieser et al. 2005), while Cassowaries (Casuarius bennetti) produce low-frequency vocalizations (ca. 23 Hz) which may extend into the infrasonic range, though those are yet to be recorded with equipment capable of resolving sounds below 23 Hz (Mack and Jones 2003). Homing pigeons (Columba livia) are known to perceive infrasound, which aids them in orientation during migration (Yodlowski et al. 1977). Given both the capacity to produce and perceive infrasound, avian infrasonic communication represents a largely unexplored possibility. Lieser et al. (2005) suggested that Capercaillie could use infrasound produced in the context of their flutter-jump display in communication. The flutter-jump display is produced by males at lek sites during the breeding season, and thus could serve as an intrasexual signal (advertising to other males) or as an intersexual signal (advertising to or attracting females). Lieser et al. (2005) recorded the calls and flutter jumps of Capercaillie (Tetrao urogallus) at a lek in the Black Forest (Germany). Sound recordings were then manipulated using Audacity (for infrasound) and Matlab scripts (for audible sound), but the software settings used to perform those manipulations were not reported (Lieser et al. 2006). To test whether Capercaillie perceive infrasonic signals, Lieser et al. (2006) played back recordings of both the infrasonic and audible sounds associated with flutter-jump displays to seven tame, captive Capercaillie females. Lieser et al. (2006) detected no behavioural response to their purported playbacks of Capercaillie infrasound, and thus concluded that infrasound was an artefactual byproduct of the flutter-jump display, with no signal function. We suggest, however, that a fundamental deficiency in the apparatus employed in the Lieser et al. (2006) playback study precluded them from reaching any definitive conclusion, and opens the door to further study. Lieser et al. (2006) used a conventional cone-based automobile subwoofer (Infinity Kappa: Harman International Industries, Stamford, CT, USA) in an unspecified enclosure to reproduce infrasound. While the computer they used to reproduce the infrasound might have been appropriate (uncertain in and of itself since the computer Communicated by F. Bairlein.

Comparative retinal morphology of the platypus

The purpose of this study is to identify evolutionary origin and fate of anatomic features of the duck-billed platypus eye. Eyes from the duck-billed platypus and four key evolutionary basal vertebrates (Pacific hagfish, north hemisphere sea lamprey, and Australian and South American lungfishes) were prepared for light microscopy. In addition to a standard panel of stains, tissues were immunostained against a variety of rod and cone opsins. Finally, published opsin sequences of platypus and several other vertebrate species were aligned and compared with immunohistochemical results. A complete scleral cartilage similar to that seen in birds, reptiles and amphibians encloses the platypus eye. This feature is present in sharks and rays, and in extant relatives of tetrapods, the lungfishes. The choroid lacks a tapetum. The retina is largely avascular and is rod-dominated, with a minority of red- and blue- cone immunoreactive photoreceptors. Like marsupials and many nonmammalian vertebrates, cones contain clear inner segment droplets. Double cones were present, a feature not found in eutherian mammals or marsupials. Evaluation of opsins indicates that red and blue immunoreactive cone opsins, but not rhodopsin, are present in the most basal of the extant species examined, the Pacific hagfish. Rhodopsin appears in the Australian and South American lungfishes, establishing emergence of this pigment in an extant relative of tetrapods. Unlike eyes of eutherian mammals, the platypus eye has retained morphologic features present in early tetrapods such as amphibians and their evolutionarily basal sister group, the lungfishes. These include scleral cartilage, double cones and cone droplets. In the platypus, as in other mammals, rod rhodopsin is the predominant photoreceptor pigment, at expense of the cone system.

Feature importance analysis in guide strand identification of microRNAs

MicroRNA (miRNA) is the negative regulator of gene expression, also known as guide strand of transient miRNA:miRNA* duplex. It is critical in maintaining the normal physiological processes such as development, differentiation, and apoptosis in many organisms. With increasing miRNA data, it is desirable to design methods to identify guide strand based on machine learning algorithms. In this study, the random forest models based on local sequence–structure features were proposed to identify miRNA in four species. The accuracies achieved were 86.51% for Homo sapiens, 81.66% for Ornithorhynchus anatinus, 82.33% for Mus musculus and 85.71% for Schmidtea mediterranea, respectively. Furthermore, the important analysis of feature elements was carried out by using the conditional feature importance strategy. The analysis results revealed that most of the significant elements were related to guanine–cytosine (GC) base pair. We believed that our method could be beneficial to annotate the function of miRNA and help the further understanding of the RNA interference mechanism.

Is body size variation in the platypus (Ornithorhynchus anatinus) associated with environmental variables?

The body size of the platypus (Ornithorhynchus anatinus) is known to vary across both its latitudinal range and relatively short geographic distances. Here we consider how variation in platypus length and weight associates with environmental variables throughout the species’ range. Based on data from over 800 individuals, a Bergmann’s cline (increased body size in regions of lower temperature) was detected across the species latitudinal range. The opposite association, however, was present at smaller scales when comparing platypus body size and temperature within southern mainland Australia, or within an individual river basin. Temperature regimes alone clearly did not dictate body size in platypuses, although disentangling the effects of different climatic variables on body size variation was difficult because of correlations amongst variables. Nevertheless, within suitable platypus habitat in south-eastern Australia, areas of relatively lower rainfall and higher temperatures were typically associated with larger-bodied platypuses. The potential benefits to larger-bodied animals living under these conditions are explored, including consideration of variation in energy expenditure and food availability. Assuming these associations with environmental variables are biologically significant, a shift in platypus body size is anticipated in the future with predicted changes in climate.

Platypus (Ornithorhynchus anatinus) body size, condition and population structure in Tasmanian river catchments: variability and potential mucormycosis impacts

Context Despite widespread interest in platypus (Ornithorhynchus anatinus) conservation, it is unclear how their fundamental morphometric and demographic characteristics differ over a range of scales. This hampers impact assessments and understanding of platypus ecology. Although the ulcerative fungal disease mucormycosis has infected platypuses in Tasmania for three decades, its population level impacts and conservation significance remain unknown. Aims This study examined morphometric and demographic patterns in Tasmanian platypuses to provide a basis for investigating impacts of mucormycosis or other anthropogenic disturbances. It also sought to identify important spatial scales of natural variability and the magnitude of seasonal variation in platypus body size, condition and population structure. The hypothesis of higher mucormycosis prevalence and mortality in adult males was also investigated. Methods Extensive live-trapping surveys were conducted from January 2008 to July 2009 in 75 streams and 18 river catchments across Tasmania including King Island. The sex, age, body size, tail volume index, health and moult condition of 195 individuals were assessed, and population age and sex structures characterised. Sampling focussed on assessing variability within and between river catchments and compared populations in river catchments with contrasting disease status. Key results Differences in platypus morphometrics within and between catchments and seasonal moulting patterns were detected. Adult males had higher fat stores than adult females, especially during winter. This study also provided the first evidence of population level consequences of disease in platypuses. The demographic group most commonly affected by mucormycosis was confirmed to be adult males. Differences in male age structure among catchments of varying disease status were consistent with the hypothesis of higher adult male mortality rates and turnover in currently affected catchments. Conclusions More than 25 years after mucormycosis was first detected in Tasmanian platypuses, the disease continues to play a low-level, ongoing role in affected populations. Implications The present study provides the first systematic multi-scale spatial investigation of platypus mucormycosis, which contributes to unravelling the epidemiology of the disease and detecting its impacts. By identifying the magnitude and important scales of morphometric and demographic differences in Tasmanian platypuses the study also assists researchers choose comparable demographic groups and spatial scales for meaningful comparisons in future impact studies.

Epigenetic modifications on X chromosomes in marsupial and monotreme mammals and implications for evolution of dosage compensation

X chromosome dosage compensation in female eutherian mammals is regulated by the noncoding Xist RNA and is associated with the differential acquisition of active and repressive histone modifications, resulting in repression of most genes on one of the two X chromosome homologs. Marsupial mammals exhibit dosage compensation; however, they lack Xist, and the mechanisms conferring epigenetic control of X chromosome dosage compensation remain elusive. Oviparous mammals, the monotremes, have multiple X chromosomes, and it is not clear whether they undergo dosage compensation and whether there is epigenetic dimorphism between homologous pairs in female monotremes. Here, using antibodies against DNA methylation, eight different histone modifications, and HP1, we conduct immunofluorescence on somatic cells of the female Australian marsupial possum Trichosurus vulpecula, the female platypus Ornithorhynchus anatinus, and control mouse cells. The two marsupial X's were different for all epigenetic features tested. In particular, unlike in the mouse, both repressive modifications, H3K9me3 and H4K20Me3, are enriched on one of the X chromosomes, and this is associated with the presence of HP1 and hypomethylation of DNA. Using sequential labeling, we determine that this DNA hypomethylated X correlates with histone marks of inactivity. These results suggest that female marsupials use a repressive histone-mediated inactivation mechanism and that this may represent an ancestral dosage compensation process that differs from eutherians that require Xist transcription and DNA methylation. In comparison to the marsupial, the monotreme exhibited no epigenetic differences between homologous X chromosomes, suggesting the absence of a dosage compensation process comparable to that in therians.

Comparative NMR studies of diffusional water permeability of red blood cells from different species: XVIII platypus (Ornithorhynchus anatinus) and saltwater crocodile (Crocodylus porosus)

As part of a programme of comparative measurements of Pd (diffusional water permeability) the RBCs (red blood cells) from an aquatic monotreme, platypus (Ornithorhynchus anatinus), and an aquatic reptile, saltwater crocodile (Crocodylus porosus) were studied. The mean diameter of platypus RBCs was estimated by light microscopy and found to be approximately 6.3 microm. Pd was measured by using an Mn2+-doping 1H NMR (nuclear magnetic resonance) technique. The Pd (cm/s) values were relatively low: approximately 2.1 x 10(-3) at 25 degrees C, 2.5 x 10(-3) at 30 degrees C, 3.4 x 10(-3) at 37 degrees C and 4.5 at 42 degrees C for the platypus RBCs and approximately 2.8 x 10(-3) at 25 degrees C, 3.2 x 10(-3) at 30 degrees C, 4.5 x 10(-3) at 37 degrees C and 5.7 x 10(-3) at 42 degrees C for the crocodile RBCs. In parallel with the low water permeability, the Ea,d (activation energy of water diffusion) was relatively high, approximately 35 kJ/mol. These results suggest that "conventional" WCPs (water channel proteins), or AQPs (aquaporins), are probably absent from the plasma membranes of RBCs from both the platypus and the saltwater crocodile.

Mammalian Peptide Isomerase: Platypus‐Type Activity Is Present in Mouse Heart

Male platypus (Ornithorhynchus anatinus) venom has a peptidyl aminoacyl L/D-isomerase (hereafter called peptide isomerase) that converts the second amino acid residue in from the N-terminus from the L- to the D-form, and vice versa. A reversed-phase high-performance liquid chromatography (RP-HPLC) assay has been developed to monitor the interconversion using synthetic hexapeptides derived from defensin-like peptide-2 (DLP-2) and DLP-4 as substrates. It was hypothesised that animals other than the platypus would have peptide isomerase with the same substrate specificity. Accordingly, eight mouse tissues were tested and heart was shown to have the activity. This is notable for being the first evidence of a peptide isomerase being present in a higher mammal and heralds finding the activity in man.