Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Sharks”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 91 records · Page 5Linked to original sources
PubMed2000

Annual social behaviour of basking sharks associated with coastal front areas.

Comparatively little is known about reproductive behaviour in wild sharks as it has proved extremely difficult to study, especially in large pelagic sharks. Here we describe annual courtship-like behaviour in the second-largest fish species, the basking shark (Cetorhinus maximus), from 25 separate episodes observed and tracked during a five-year study period (1995-1999) off south-west England. Social behaviours observed between paired, or three or four, sharks were consistent with courtship behaviours seen in other shark species, namely nose-to-tail following, close following, close flank approach, parallel and echelon swimming. Mature individuals between 5 and 8 m total body length (L(T)) exhibited these behaviours whereas smaller sharks (3-4 m L(T)) did not. Lead individuals were identified as female on a number of occasions and interactions were prolonged; the longest continuous observation of socializing was 1.8 h, although intermittent track data indicates bouts may last for up to 5-6 h. Locations of courtship-like behaviour events were not distributed randomly and were significantly associated with thermal fronts. Our results indicate that putative courtship behaviour occurs between May and July along oceanographic fronts, probably as a consequence of individuals aggregating to forage in rich prey patches before initiating courtship. Thus, locating the richest prey patches along fronts may be important for basking sharks to find mates as well as food in the pelagic ecosystem. As courtship-like behaviours occur annually off south-west England we speculate that this region may represent an annual breeding area for this protected species, but mating itself probably takes place at depth as it was not seen at the surface.

Animals↗
PubMed1992

The primary structure of fatty-acid-binding protein from nurse shark liver. Structural and evolutionary relationship to the mammalian fatty-acid-binding protein family.

The primary structure of a fatty-acid-binding protein (FABP) isolated from the liver of the nurse shark (Ginglymostoma cirratum) was determined by high-performance tandem mass spectrometry (employing multichannel array detection) and Edman degradation. Shark liver FABP consists of 132 amino acids with an acetylated N-terminal valine. The chemical molecular mass of the intact protein determined by electrospray ionization mass spectrometry (Mr = 15124 +/- 2.5) was in good agreement with that calculated from the amino acid sequence (Mr = 15121.3). The amino acid sequence of shark liver FABP displays significantly greater similarity to the FABP expressed in mammalian heart, peripheral nerve myelin and adipose tissue (61-53% sequence similarity) than to the FABP expressed in mammalian liver (22% similarity). Phylogenetic trees derived from the comparison of the shark liver FABP amino acid sequence with the members of the mammalian fatty-acid/retinoid-binding protein gene family indicate the initial divergence of an ancestral gene into two major subfamilies: one comprising the genes for mammalian liver FABP and gastrotropin, the other comprising the genes for mammalian cellular retinol-binding proteins I and II, cellular retinoic-acid-binding protein myelin P2 protein, adipocyte FABP, heart FABP and shark liver FABP, the latter having diverged from the ancestral gene that ultimately gave rise to the present day mammalian heart-FABP, adipocyte FABP and myelin P2 protein sequences. The sequence for intestinal FABP from the rat could be assigned to either subfamily, depending on the approach used for phylogenetic tree construction, but clearly diverged at a relatively early evolutionary time point. Indeed, sequences proximately ancestral or closely related to mammalian intestinal FABP, liver FABP, gastrotropin and the retinoid-binding group of proteins appear to have arisen prior to the divergence of shark liver FABP and should therefore also be present in elasmobranchs. The presence in shark liver of an FABP which differs substantially in primary structure from mammalian liver FABP, while being closely related to the FABP expressed in mammalian heart muscle, peripheral nerve myelin and adipocytes, opens a further dimension regarding the question of the existence of structure-dependent and tissue-specific specialization of FABP function in lipid metabolism.

Amino Acid Sequence↗
PubMed2004

Molecular evolution of shark and other vertebrate DNases I.

We purified pancreatic deoxyribonuclease I (DNase I) from the shark Heterodontus japonicus using three-step column chromatography. Although its enzymatic properties resembled those of other vertebrate DNases I, shark DNase I was unique in being a basic protein. Full-length cDNAs encoding the DNases I of two shark species, H. japonicus and Triakis scyllia, were constructed from their total pancreatic RNAs using RACE. Nucleotide sequence analyses revealed two structural alterations unique to shark enzymes: substitution of two Cys residues at positions 101 and 104 (which are well conserved in all other vertebrate DNases I) and insertion of an additional Thr or Asn residue into an essential Ca(2+)-binding site. Site-directed mutagenesis of shark DNase I indicated that both of these alterations reduced the stability of the enzyme. When the signal sequence region of human DNase I (which has a high alpha-helical structure content) was replaced with its amphibian, fish and shark counterparts (which have low alpha-helical structure contents), the activity expressed by the chimeric mutant constructs in transfected mammalian cells was approximately half that of the wild-type enzyme. In contrast, substitution of the human signal sequence region into the amphibian, fish and shark enzymes produced higher activity compared with the wild-types. The vertebrate DNase I family may have acquired high stability and effective expression of the enzyme protein through structural alterations in both the mature protein and its signal sequence regions during molecular evolution.

Amino Acid Sequence↗
PubMed2006

Global estimates of shark catches using trade records from commercial markets.

Despite growing concerns about overexploitation of sharks, lack of accurate, species-specific harvest data often hampers quantitative stock assessment. In such cases, trade studies can provide insights into exploitation unavailable from traditional monitoring. We applied Bayesian statistical methods to trade data in combination with genetic identification to estimate by species, the annual number of globally traded shark fins, the most commercially valuable product from a group of species often unrecorded in harvest statistics. Our results provide the first fishery-independent estimate of the scale of shark catches worldwide and indicate that shark biomass in the fin trade is three to four times higher than shark catch figures reported in the only global data base. Comparison of our estimates to approximated stock assessment reference points for one of the most commonly traded species, blue shark, suggests that current trade volumes in numbers of sharks are close to or possibly exceeding the maximum sustainable yield levels.

Animals↗
PubMed1993

Sequence similarities of myelin basic protein promoters from mouse and shark: implications for the control of gene expression in myelinating cells.

To better understand the cell type-specific and coordinated regulation of the myelin protein genes, we cloned and sequenced the shark myelin basic protein (MBP) promoter. An alignment of the shark sequence with the corresponding mouse sequence showed striking similarities. These similarities, together with the results from expression experiments, define two major regions (A and B) within the MBP promoter. Region A is located immediately 5' to the transcription initiation sites and includes five sequences thought to be cis-acting domains. These domains include two boxes of 13 and 12 nucleotides, respectively, separated from each other by 10 nucleotides, an MBP enhancer, and GC, CCAAT, and TATA boxes. Region A also contains a putative exon that codes for 35 amino acids of an unidentified polypeptide. Region B, which is located adjacent to the 5' end of region A, contains two boxes that are 10 and 11 nucleotides long, respectively, and are identical in mouse and shark. We have previously cloned and sequenced the shark glycoprotein zero (P0) promoter. A comparison between the sequences of the rat and shark P0 promoters shows three conserved regions in addition to CCAAT and TATA boxes. The shark P0 promoter is active in the CNS and PNS, and contains a sequence of 13 nucleotides that is located at -159 from the initiation of transcription and is similar to that of the MBP enhancer. The mammalian P0 promoter is active exclusively in the adult PNS and contains a sequence similar to that of the MBP enhancer located adjacent to the 3' side of the transcription initiation site. Sequence similarities and differences between the promoters of the mammalian and shark myelin protein genes will help to identify the basis for the cell type-specific and coordinated expression of these genes.

Animals↗
PubMed1998

What sharks can tell us about the evolution of MHC genes.

Similarity in structural features would argue that sharks possess class I, class IIA and class IIB genes, coding for classical peptide-presenting molecules, as well as non-classical class I genes. Some aspects of shark major histocompatibility complex genes are similar to teleost genes and others are similar to tetrapod genes. Shark class I genes form a monophyletic group, as also seen for tetrapods, but the classical and nonclassical genes form two orthologous clades, as seen for teleosts. Teleost class I genes arose independently at least four different times with the nonclassical genes of ray-finned fishes and all the shark and lobe-finned fish class I genes forming 1 clade. The ray-finned fish classical class I genes arose separately. In phylogenetic trees of class II alpha 2 and beta 2 domains, the shark and tetrapod genes cluster more closely than the teleost genes and, unlike the teleost sequences, the class II alpha 1 domains of sharks and tetrapods lack cysteines. On the other hand, both shark and teleost genes display sequence motifs in the antigen-binding cleft that have persisted over very long time periods. The similarities may reflect common selective pressures on species in aqueous environments while differences may be due to different evolutionary rates.

Amino Acid Sequence↗
PubMed2001

Demonstration of inhibitory effect of oral shark cartilage on basic fibroblast growth factor-induced angiogenesis in the rabbit cornea.

Several angiogenic inhibitors have been obtained from shark cartilage, some of these are currently in clinical trials for assessment of safety and therapeutic efficacy in humans. Still, shark cartilage taken orally is commonly used in alternative and complimentary medicine for various ailments including serious diseases such as cancer. However, only few studies of oral shark cartilage have demonstrated pharmacological effects in experimental animals or patients, to indicate safe doses with sufficient bioavailability. In the present study we demonstrated the antiangiogenic properties of oral shark cartilage in the rabbit cornea model. Slow-release, polymethylmetacrylate pellets containing basic fibroblast growth factor (bFGF) were surgically implanted in the rabbit cornea to stimulate neovascularization scored by stereo microscopy. Powdered shark cartilage (PSC; commercial product) was tested orally along with a water-soluble fraction (WSF) of this cartilage product which was tested by local application. Animals were treated with oral dosages of 100 mg/kg PSC or 200 mg/kg thalidomide as positive control. Pellets containing WSF (50, 100 or 200 microg/pellet) or bFGF-inhibitor pentosan polysulfate were implanted adjacent to the bFGF pellet. Oral shark cartilage inhibited bFGF-induced angiogenesis, as did oral thalidomide, in this in vivo model. WSF and pentosan polysulfate was shown to block neovascularization in the cornea when applied locally. This study demonstrates that in the rabbit, oral shark cartilage appears to produce systemic levels of angiogenesis inhibitors that can exert their effect at the cornea.

Administration, Oral↗
PubMed2001

Gill lesions associated with Erpocotyle tiburonis (Monogenea: Hexabothriidae) on wild and aquarium-held bonnethead sharks (Sphyrna tiburo).

Gill lesions associated with infections of Erpocotyle tiburonis (Brooks, 1934) (Monogenea: Hexabothriidae) on wild bonnethead sharks (Sphyrna tiburo (L., 1758) (Carcharhiniformes: Sphyrinidae)) were compared with those on aquarium-held ones using light and scanning electron microscopy. Uninfected gill filaments had slender, triangular, smooth-surfaced lamellae and interlamellar water channels that were approximately equal in size. Four wild sharks were each infected by 3-11 widely separated adult E. tiburonis, and 1 of these sharks hosted a juvenile specimen. Lamellae flanking or touching adult E. tiburonis were pushed aside or bent, but were otherwise identical to those of uninfected filaments. Two aquarium-held sharks were each infected by hundreds of juvenile and adult E. tiburonis. In these sharks, lamellae near juveniles were pushed apart or bent, but were otherwise normal, whereas a thick, ragged-surfaced layer of hyperplastic epithelium both filled interlamellar water channels and partially or completely covered lamellae near adults. Results of this study suggest that the intense infections of E. tiburonis were facilitated by captivity and caused severe hyperplastic lesions that ultimately led to the death of the sharks by reducing or blocking the respiratory water flow over lamellae and thus reducing the exchange of gases and ions across the lamellar epithelium. In contrast, the wild sharks were infected by fewer worms and exhibited relatively minor lesions.

Animals↗
PubMed2001

Rapid and simultaneous identification of body parts from the morphologically similar sharks Carcharhinus obscurus and Carcharhinus plumbeus (Carcharhinidae) using multiplex PCR.

Many commercially exploited carcharhinid sharks are difficult to identify to species owing to extensive morphological similarities. This problem is severely exacerbated when it comes to identifying detached shark fins, and the finless and headless shark carasses typically sold in markets. To assist in the acquisition of urgently needed conservation and management data on shark catch and trade, we have developed a highly streamlined approach based on multiplex polymerase chain reaction (PCR) that uses species-specific primers derived from nuclear ribosomal ITS2 sequences to achieve rapid species identification of shark body parts. Here we demonstrate the utility of this approach for identifying fins and flesh from two globally distributed, morphologically very similar carcharhinid sharks (Carcharhinus obscurus and Carcharhinus plumbeus) intensively targeted in fisheries worldwide, and often confused for each other even as whole animals. The assay is conducted in a 4-primer multiplex format that is structured to simultaneously achieve the following efficiency and cost-reduction objectives: it requires only a single-tube amplification reaction for species diagnosis, it incorporates an internal positive control to allow detection of false-negative results, and it is novel in that it allows species identification even when DNAs from two species are combined in the same tube during the PCR reaction. The latter innovation reduces the required effort for screening a set of unknown samples by 50%. The streamlined approach illustrated here should be amenable for use in a shark conservation and management context where large numbers of samples typically need to be screened; the approach shown may also provide a model for a rapid diagnostic method applicable to species identification in general.

Journal Article↗
PubMed2024

Comparative genomics illuminates karyotype and sex chromosome evolution of sharks.

Chondrichthyes is an important lineage to reconstruct the evolutionary history of vertebrates. Here, we analyzed genome synteny for six chondrichthyan chromosome-level genomes. Our comparative analysis reveals a slow evolutionary rate of chromosomal changes, with infrequent but independent fusions observed in sharks, skates, and chimaeras. The chondrichthyan common ancestor had a proto-vertebrate-like karyotype, including the presence of 18 microchromosome pairs. The X chromosome is a conversed microchromosome shared by all sharks, suggesting a likely common origin of the sex chromosome at least 181 million years ago. We characterized the Y chromosomes of two sharks that are highly differentiated from the X except for a small young evolutionary stratum and a small pseudoautosomal region. We found that shark sex chromosomes lack global dosage compensation but that dosage-sensitive genes are locally compensated. Our study on shark chromosome evolution enhances our understanding of shark sex chromosomes and vertebrate chromosome evolution.

Animals↗
PubMed1978

Visual discrimination following partial telencephalic ablations in nurse sharks (Ginglymostoma cirratum).

An instrumental conditioning task was used to examine the role of the nurse shark telencephalon in black-white (BW) and horizontal-vertical stripes (HV) discrimination performance. In the first experiment, subjects initially received either bilateral anterior telencephalic control lesions or bilateral posterior telencephalic lesions aimed at destroying the central telencephalic nuclei (CN), which are known to receive direct input from the thalamic visual area. Postoperatively, the sharks were trained first on BW and then on HV. Those with anterior lesions learned both tasks as rapidly as unoperated subjects. Those with posterior lesions exhibited visual discrimination deficits related to the amount of damage to the CN and its connecting pathways. Severe damage resulted in an inability to learn either task but caused no impairments in motivation or general learning ability. In the second experiment, the sharks were first trained on BW and HV and then operated. Suction ablations were used to remove various portions of the CN. Sharks with 10% or less damage to the CN retained the preoperatively acquired discriminations almost perfectly. Those with 11-50% damage had to be retrained on both tasks. Almost total removal of the CN produced behavioral indications of blindness along with an inability to perform above the chance level on BW despite excellent retention of both discriminations over a 28-day period before surgery. It appears, however, that such sharks can still detect light. These results implicate the central telencephalic nuclei in the control of visually guided behavior in sharks.

Animals↗
PubMed2003

Inter- and intraspecific variation in the distribution and number of pit organs (free neuromasts) of sharks and rays.

The distribution of pit organs (free neuromasts) has previously been documented for several species of pelagic sharks, but is relatively poorly known for rays and bottom-dwelling (demersal) sharks. In the present study, the complete distribution of pit organs was mapped in the demersal sharks Heterodontus portusjacksoni, Orectolobus maculatus, Hemiscyllium ocellatum, Chiloscyllium punctatum, and Asymbolus analis, and the rays Rhinobatos typus, Aptychotrema rostrata, Trygonorrhina sp. A, Raja sp. A, and Myliobatis australis. All of these species had pit organs scattered over the dorsolateral surface. The sharks also had "mandibular" pit organs (and "umbilical" pit organs in C. punctatum and A. analis) on the ventral surface, while pit organs were sparse or absent on the ventral surface of rays. All of the species examined here, except for M. australis, also had a "spiracular" group of pit organs adjacent to the eye and/or spiracle. Spiracular pit organs were also recorded for the sawshark Pristiophorus sp. A and the skate Pavoraja nitida, although the remainder of pit organs were not mapped in these species. The distribution and number of pit organs varied both within and among species. Pit organ distribution was asymmetrical in each individual examined, but no particular trend towards left or right "handedness" was observed in any species. Although rays have been thought to have fewer pit organs than sharks in general, this was not the case in the present study. All of the species examined here had few pit organs compared to the pelagic sharks previously documented, but it is not clear whether this is due to ecological or phylogenetic causes.

Animals↗
PubMed2001

Functional morphology of the pectoral fins in bamboo sharks, Chiloscyllium plagiosum: benthic vs. pelagic station-holding.

Bamboo sharks (Chiloscyllium plagiosum) are primarily benthic and use their relatively flexible pectoral and pelvic fins to rest on and move about the substrate. We examined the morphology of the pectoral fins and investigated their locomotory function to determine if pectoral fin function during both benthic station-holding and pelagic swimming differs from fin function described previously in leopard sharks, Triakis semifasciata. We used three-dimensional kinematics and digital particle image velocimetry (DPIV) to quantify pectoral fin function in five white-spotted bamboo sharks, C. plagiosum, during four behaviors: holding station on the substrate, steady horizontal swimming, and rising and sinking during swimming. During benthic station-holding in current flow, bamboo sharks decrease body angle and adjust pectoral fin angle to shed a clockwise fluid vortex. This vortex generates negative lift more than eight times that produced during open water vertical maneuvering and also results in an upstream flow that pushes against the posterior surface of the pectoral fin to oppose drag. In contrast, there is no evidence of significant lift force in the wake of the pectoral fin during steady horizontal swimming. The pectoral fin is held concave downward and at a negative dihedral angle during steady horizontal swimming, promoting maneuverability rather than stability, although this negative dihedral angle is much less than that observed previously in sturgeon and leopard sharks. During sinking, the pectoral fins are held concave upward and shed a clockwise vortex with a negative lift force, while in rising the pectoral fin is held concave downward and sheds a counterclockwise vortex with a positive lift force. Bamboo sharks appear to sacrifice maneuverability for stability when locomoting in the water column and use their relatively flexible fins to generate strong negative lift forces when holding position on the substrate and to enhance stability when swimming in the water column.

Animals↗
PubMed1991

Multiple prismatic calcium phosphate layers in the jaws of present-day sharks (Chondrichthyes; Selachii).

Jaws of large individuals, over 2 m in total length, of the shark species Carcharodon carcharias (great white shark) and Isurus oxyrinchus (mako shark) of the family Lamnidae, and Galeocerdo cuvieri (tiger shark) and Carcharhinus leucas (bull shark) of the family Carcharhinidae were found to have multiple, up to five, layers of prismatic calcium phosphate surrounding the cartilages. Smaller individuals of these species and other known species of living chondrichthyans have only one layer of prismatic calcium phosphate surrounding the cartilages, as also do most species of fossil chondrichthyans. Two exceptions are the fossil shark genera Xenacanthus and Tamiobatis. Where it is found in living forms, this multiple layered calcification does not appear to be phylogenetic, as it appears to be lacking in other lamnid and carcharhinid genera and species. Rather it appears to be functional, only appearing in larger individuals and species of these two groups, and hence may be necessary to strengthen the jaw cartilages of such individuals for biting.

Animals↗
PubMed2003

Osmotic, sodium, carbon dioxide and acid-base state of the Port Jackson shark, Heterodontus portusjacksoni, in response to lowered salinity.

In marine elasmobranch fish the consequences for CO2 and acid-base state of moving into low salinity water are not well described. Sub-adult Port Jackson sharks, Heterodontus portusjacksoni, occasionally enter brackish water and survive in 50% seawater (SW). The unidirectional Na efflux and content, plasma volume, glomerular filtration rate (GFR), body mass, as well as CO2 and acid-base state in H. portusjacksoni were investigated following transfer from 100% SW to 75% SW and then to 50% SW. A rapid water influx resulted in a doubling of the plasma volume within 24 h in sharks in 75% SW and an 11% increase in body weight. Osmotic water influx was only partially offset by a doubling of the GFR. There was a approximately 40% decrease in plasma [Na] through a transiently elevated Na clearance and haemodilution. The result was a decrease in the inward gradient for Na+ together with reductions of nearly 50% in CO2 and buffer capacity. The sharks remained hypo-natric to 50% SW by partially conforming to the decrease in external osmotic pressure and avoided the need for active Na+ uptake. The gradient for Na+ efflux would by extrapolation approach zero at approximately 27% SW which may of itself prove a lethal internal dilution. In sharks transferred to 75% SW, a small transient hypercapnia and a later temporary metabolic alkalosis were all largely explained through anaemia promoting loss of CO2 and buffer capacity. In sharks transferred to 50% SW the metabolic alkalosis persisted until the end of the 1-week trial. Within the erythrocytes, increased pH was consequent on the large decrease in haemoglobin content exhibited by the sharks, which caused a large reduction in intracellular buffer. In water as dilute as 50% SW there was no evidence of specific effects on the mechanisms of management of CO2 or H+ excretion but rather significant and indirect effects of the severe haemodilution.

Acclimatization↗
PubMed1988

Induction of cell-mediated cytotoxicity by shark 19S IgM.

Plasma from unimmunized nurse sharks can mediate a reaction similar to antibody-dependent cell-mediated cytotoxicity (ADCC). Normal shark plasma contains numerous natural antibodies reactive with a variety of antigens, including the target employed. Adsorption of plasma with target cells removed a significant amount of activity, suggesting involvement of antibody. Purified 19s IgM was shown to be a component of shark plasma capable of inducing cytotoxicity. These cytotoxic reactions differ from observations in homeothermic vertebrates in that shark immunoglobulin appears to bind more avidly to the effector cells than to the targets. The effector leukocytes are glass adherent, but not susceptible to carbonyl iron treatment, which clearly separates them from the phagocytic effectors of spontaneous cytotoxicity. Thus, the shark possesses leukocytes with the capability of mediating an ADCC-like reaction. These leukocytes, in concert with those mediating spontaneous cytotoxicity, could provide the shark with an effective immunosurveillance system. These data also indicate that ADCC mechanisms, with IgM as the primary effector molecule, appeared early in evolution.

Animals↗
PubMedDate not supplied

Antibody production in sharks and humans: a role for natural antibodies.

Although gene segments specifying Igs of all vertebrates show clear homology, their arrangements differ markedly, thereby suggesting that the mechanisms for the generation of diversity and for the regulation of gene expression may be quite distinct. In the sandbar shark, light chain gene segments are distributed as apparently independent clusters consisting of V, J, and C elements that require rearrangement for expression. The usual distance between V and C in the clusters is 3 kb but larger clusters occur. The V, J, and C elements are clearly homologous to those of human lambda chains. Shark Igs resemble mammalian IgM in structure and gene similarity. IgM may comprise as much as 50% of serum proteins in the shark. By contrast, IgM in humans comprises less than 5%. Human autoantibodies usually are IgM. These show little dependence on thymic function for expression and tend to increase with age. We have carried out a study of the capacity of Igs of unimmunized sharks and people (normals and patients suffering from autoimmune diseases) to react against a panel of antigens, including those usually considered autoantibodies, such as thyroglobulin and single-stranded DNA. Sharks and humans possess IgM antibodies that react with thyroglobulin and ssDNA. Affinity-purified natural shark antibodies to thyroglobulin or ssDNA constitute small fractions of total IgM. They illustrate extensive cross-reactivity comparable to that shown by polyspecific IgM autoantibodies produced by human B cells (CD5+) that appear early in ontogeny.

Amino Acid Sequence↗
PubMed1986

Purification and characterization of creatine kinase isozymes from the nurse shark Ginglymostoma cirratum.

Creatine kinase from nurse shark brain and muscle has been purified to apparent homogeneity. In contrast to creatine kinases from most other vertebrate species, the muscle isozyme and the brain isozyme from nurse shark migrate closely in electrophoresis and, unusually, the muscle isozyme is anodal to the brain isozyme. The isoelectric points are 5.3 and 6.2 for the muscle and brain isozymes, respectively. The purified brain preparation also contains a second active protein with pI 6.0. The amino acid content of the muscle isozyme is compared with other isozymes of creatine kinase using the Metzger Difference Index as an estimation of compositional relatedness. All comparisons show a high degree of compositional similarity including arginine kinase from lobster muscle. The muscle isozyme is marginally more resistant to temperature inactivation than the brain isozyme; the muscle protein does not exhibit unusual stability towards high concentrations of urea. Kinetic analysis of the muscle isozyme reveals Michaelis constants of 1.6 mM MgATP, 12 mM creatine, 1.2 mM MgADP and 50 mM creatine phosphate. Dissociation constants for the same substrate from the binary and ternary enzyme-substrate complex do not differ significantly, indicating limited cooperatively in substrate binding. Enzyme activity is inhibited by small planar anions, most severely by nitrate. Shark muscle creatine kinase hybridizes in vitro with rabbit muscle or monkey brain creatine kinase; shark brain isozyme hybridizes with monkey brain or rabbit brain creatine kinase. Shark muscle and shark brain isozymes, under a wide range of conditions, failed to produce a detectable hybrid.

Amino Acids↗