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At least 181 records · Page 10Linked to original sources
PubMed2001

Computer-assisted evaluation of isoelectric focusing patterns in electrophoretic gels: identification of smoothhounds (Mustelus mustelus, Mustelus asterias) and comparison with lower value shark species.

In this work, the most commercially important Selachian species, smoothhound (Mustelus mustelus) and starry smoothhound (Mustelus asterias), have been identified by polyacrylamide isoelectric focusing (IEF-PAGE), along with several shark species of minor commercial value. In Italy, these two smoothhound species are commonly subjected to fraudulent substitution with lesser valued sharks. After the electrophoretic runs, the band patterns of the two Mustelus species were compared with those of dogfish (Scyliorhinus canicula), spurdog (Squalus acanthias), blue shark (Prionace glauca) and black-mouthed dogfish (Galeus melanostomus), both visually and with gel analysis software. The actual isoelectric points were then submitted to cluster analysis to differentiate the single species, despite the possible occurrence of electrophoretic variations or protein polymorphism. Every shark showed species-specific band patterns and could therefore be well differentiated, as confirmed by statistical analysis.

Acrylic Resins↗
PubMed2005

Dorsal fin in the white shark, Carcharodon carcharias: a dynamic stabilizer for fast swimming.

Transverse sections of the skin in the dorsal fin of the white shark, Carcharodon carcharias, tiger shark, Galeocerdo cuvier, and spotted raggedtooth shark, Carcharias taurus, show large numbers of dermal fiber bundles, which extend from the body into the fin. The bundles are tightly grouped together in staggered formation (not arranged in a straight line or in rows). This arrangement of dermal fibers gives tensile strength without impeding fiber movement. Tangential sections indicate that the fibers in all three species are strained and lie at angles in excess of 60 degrees . Of the three species investigated the dermal fibers in C. carcharias are the most densely concentrated and extend furthest distally along the dorsal fin. The overall results indicate that the dorsal fin of C. carcharias functions as a dynamic stabilizer and that the dermal fibers are crucial to this role. The fibers work like riggings that stabilize a ship's mast. During fast swimming, when the problems of yaw and roll are greatest, hydrostatic pressure within the shark increases and the fibers around the body, including in the dorsal fin, become taut, thereby stiffening the fin. During slow swimming and feeding the hydrostatic pressure is reduced, the fibers are slackened, and the muscles are able to exert greater bending forces on the fin via the radials and ceratotrichia. In C. carcharias there is a trade-off for greater stiffness of the dorsal fin against flexibility.

Animal Structures↗
PubMed2005

Olfactory morphology of carcharhinid and sphyrnid sharks: does the cephalofoil confer a sensory advantage?

Many hypotheses have been advanced to explain the adaptive significance of the sphyrnid cephalofoil, including potential advantages of spacing the olfactory organs at the distal tips of the broad surface. We employed comparative morphology to test whether the sphyrnid cephalofoil provides better stereo-olfaction, increases olfactory acuity, and samples a greater volume of the medium compared to the situation in carcharhiniform sharks. The broadly spaced nares provide sphyrnid species with a significantly greater separation between the olfactory rosettes, which could lead to an enhanced ability to resolve odor gradients. In addition, most sphyrnid species possess prenarial grooves that greatly increase the volume of water sampled by the nares and thus increase the probability of odorant encounter. However, despite a much greater head width, and a significantly greater number of olfactory lamellae, scalloped hammerhead sharks do not possess a greater amount of olfactory epithelial surface area than the carcharhiniform sandbar sharks. Therefore, sphyrnid sharks might not possess any greater olfactory acuity than carcharhinids. Despite this, there are clear olfactory advantages to the cephalofoil head morphology that could have led to its evolution, persistence, and diversification. persistence, and diversification.

Animals↗
PubMed2005

Caudal fin in the white shark, Carcharodon carcharias (Lamnidae): a dynamic propeller for fast, efficient swimming.

The caudal peduncle and caudal fin of Carcharodon carcharias together form a dynamic locomotory structure. The caudal peduncle is a highly modified, dorsoventrally compressed and rigid structure that facilitates the oscillations of the caudal fin. Its stiffness appears to be principally achieved by a thick layer of adipose tissue ranging from 28-37% of its cross-sectional area, reinforced by cross-woven collagen fibers. Numerous overlying layers of collagen fibers of the stratum compactum, oriented in steep left- and right-handed helices (approximately 65 degrees to the shark's long axis), prevent bowstringing of the perimysial fibers, which lie just below the dermal layer. Perimysial fibers, muscles, and the notochord are restricted to the dorsal lobe of the caudal fin and comprise the bulk of its mass. Adipose tissue reinforces the leading edge of the dorsal lobe of the caudal fin and contributes to maintaining the ideal cross-sectional geometry required of an advanced hydrofoil. Most of the mass of the ventral lobe consists of the ceratotrichia or fin rays separated by thin partitions of connective tissue. Dermal fibers of the stratum compactum of the dorsal lobe occur in numerous distinct layers. The layers are more complex than in other sharks and appear to reflect a hierarchical development in C. carcharias. The fiber layer comprises a number of thick fiber bundles along the height of the layer and the layers get thicker deeper into the stratum compactum. Each of these layers alternates with a layer a single fiber-bundle deep, a formation thought to give stability to the stratum compactum and to enable freer movements of the fiber system. In tangential sections of the stratum compactum the fiber bundles in the dorsal lobe can be seen oriented with respect to the long axis of the shark at approximately 55-60 degrees in left- and right-handed helices. Because of the backward sweep of the dorsal lobe (approximately 55 degrees to the shark's long axis) the right-handed fibers also parallel the lobe's long axis. In the dorsal lobe, ceratotrichia are present only along the leading edge (embedded within connective tissue), apparently as reinforcement. Stratum compactum fiber bundles of the ventral lobe, viewed in transverse section, lack the well-ordered distinctive layers of the dorsal lobe, but rather occur as irregularly arranged masses of tightly compacted fiber bundles of various sizes. In tangential sections the fiber bundles are oriented at angles of approximately 60 degrees, generally in one direction, i.e., lacking the left- and right-handed helical pattern. Tensile load tests on the caudal fin indicate high passive resistance to bending by the skin. The shear modulus G showed that the skin's contribution to stiffness (average values from three specimens at radians 0.52 and 1.05) is 33.5% for the dorsal lobe and 41.8% for the ventral. The load tests also indicate greater bending stiffness of the ventral lobe compared to the dorsal. Overall, the anatomy and mechanics of the dorsal lobe of C. carcharias facilitate greater control of movement compared to the ventral lobe. The helical fiber architecture near the surface of the caudal fin is analogous to strengthening of a thin cylinder in engineering. High fiber angles along the span of the dorsal lobe are considered ideal for resisting the bending stresses that the lobe is subjected to during the locomotory beat cycle. They are also ideal for storing strain energy during bending of the lobe and consequently may be of value in facilitating the recovery stroke. The complex fiber architecture of the caudal fin and caudal peduncle of C. carcharias provides considerable potential for an elastic mechanism in the animal's swimming motions and consequently for energy conservation.

Animals↗
PubMed1985

Ameloblastic secretion and calcification of the enamel layer in shark teeth.

Tooth primordia at early stages of mineralization in the sharks Negaprion brevirostris and Triaenodon obesus were examined electron microscopically for evidence of ameloblastic secretion and its relation to calcification of the enamel (enameloid) layer. Ameloblasts are polarized with most of the mitochondria and all of the Golgi dictyosomes localized in the infranuclear end of the cell toward the squamous outer cells of the enamel organ. Endoplasmic reticular membranes and ribosomes are also abundant in this region. Ameloblastic vesicles bud from the Golgi membranes and evidently move through perinuclear and supranuclear zones to accumulate at the apical end of the cell. The vesicles secrete their contents through the apical cell membrane in merocrine fashion and appear to contribute precursor material both for the basal lamina and the enameline matrix. The enamel layer consists of four zones: a juxta-laminar zone containing newly polymerized mineralizing fibrils (tubules); a pre-enamel zone of assembly of matrix constituents; palisadal zones of mineralizing fibrils (tubules); and interpalisadal zones containing granular amorphous matrix, fine unit fibrils, and giant cross-banded fibers with a periodicity of 17.9 nm. It seems probable that amorphous, non-mineralizing fibrillar and mineralizing fibrillar constituents of the matrix are all products of ameloblastic secretion. Odontoblastic processes are tightly embedded in the matrix of the palisadal zones and do not appear to be secretory at the stages investigated. The shark tooth enamel layer is considered homologous with that of other vertebrates with respect to origin of its mineralizing fibrils from the innerental epithelium. The term enameloid is appropriate to connote the histological distinction that the enamel layer contains odontoblastic processes but should not signify that shark tooth enamel is a modified type of dentine. How amelogenins and/or enamelins secreted by amelo- blasts in the shark and other vertebrates are related to nucleation and growth of enamel crystallites is still not known.

Ameloblasts↗
PubMed1993

Molecular cloning of the myelin basic proteins in the shark, Squalus acanthias, and the ray, Raja erinacia.

Myelin basic proteins (MBPs) are a family of alternatively spliced isoforms present in myelin sheaths of most vertebrates. A reverse transcriptase-polymerase chain reaction (RT-PCR) approach was used to clone MBP isoforms in species representing two superorders of elasmobranchs: Squalus acanthias, representing Squalomorph sharks, and Raja erinacia, representing Batoidea rays. Two products were generated from each species. The larger product encoded a 155 amino acid protein, the same size as MBPs from two Galeomorph sharks, Heterodontus francisci and Carcharhinus obscurus, which, based upon alignment with other vertebrate MBPs, contained six of the seven MBP exons; only exon II was absent. The smaller product encoded a 141 amino acid protein that lacked exon II and exon V. There were 26 and 30 nucleotide differences between Squalus and Heterodontus, and Raja and Heterodontus, respectively. Sequences from Squalus and Raja were far more similar, having only five nucleotide differences. Both isoforms of elasmobranch MBP contain 18.5% basic (lysine plus arginine) amino acids, compared with 17.5% in mammalian MBPs comprised of the corresponding exons. Northern blot analysis of whole brain total RNA revealed a single band of 2.5 kb in Squalus, and three bands of 1.2, 1.4, and 2.3 kb in Raja. The finding that MBPs of a Squalomorph shark and a Batoidea ray are closer to one another than either is to the Galeomorph sharks suggests that MBP sequence information may prove useful in classifying modern day Chondrichthytes.

Animals↗
PubMed1992

Primary structure of a protein isolated from reef shark (Carcharhinus springeri) cartilage that is similar to the mammalian C-type lectin homolog, tetranectin.

During the course of characterization of low molecular weight proteins in cartilage, we have isolated a protein from reef shark (Carcharhinus springeri) cartilage that bears a striking resemblance to the tetranectin monomer originally described by Clemmensen et al. (1986, Eur. J. Biochem. 156, 327-333). The protein was isolated by extraction of neural arch cartilage with 4 M guanidine hydrochloride, dialysis of the extract to bring the guanidine to 0.4 M (reassociating proteoglycan aggregates), followed by cesium chloride density gradient removal of the proteoglycans. The amino acid sequence had 166 amino acids and a calculated molecular weight of 18,430. The shark protein was 45% identical to human tetranectin, indicating that it was in the family of mammalian C-type lectins and that it was likely to be a shark analog of human tetranectin. The function of tetranectin is unknown; it was originally isolated by virtue of its affinity for the kringle-4 domain of plasminogen. Sequence comparison of human tetranectin and the shark-derived protein gives clues to potentially important regions of the molecule.

Amino Acid Sequence↗
PubMed1994

Molecular modeling and electrostatic potential calculations on chemically modified Cu,Zn superoxide dismutases from Bos taurus and shark Prionace glauca: role of Lys134 in electrostatically steering the substrate to the active site.

The three-dimensional structure of Cu,Zn superoxide dismutase (SOD) from the shark Prionace glauca was homology modeled on the structure of the bovine enzyme used as a template. Shark SOD displays the conservative substitution of one of the residues involved in the electrostatic guidance of superoxide toward the active site of the enzyme, i.e., Lys134, which is replaced by arginine. The association rate, calculated by brownian dynamics simulations incorporating electrostatic terms, and the enzyme reaction rate, measured by the pulse radiolysis method, were found to be identical for both bovine and shark SODs. In order to quantify the role of Lys134 in electrostatically steering the superoxide to the active site, chemical modification of the lysine residues by carbamoylation was carried out on both bovine and shark SODs. Experimental determination of the enzymatic reaction rate indicated that the charge located on the residue 134 gives 19% contribution to the guidance of superoxide anion at low ionic strength. This value matches the association rates predicted by brownian dynamics.

Amino Acid Sequence↗
PubMed1984

Synthetic surfactants: a new approach to the development of shark repellents.

The toxic and shark repellent secretion of Pardachirus marmoratus (PMC) and a series of 15 surfactants and industrial detergents were assayed for their lethality to fish, termination of shark's tonic immobility and feeding inhibition of aggressive, hungry lemon sharks. Sodium and lithium lauryl sulfate salts were more potent than PMC in all three bioassays. Graduated activity, from mildly repellent to inactive, was demonstrated by several other surfactants. The abundance, versatility, chemical stability, modifiability, and low price of detergents justify their use in further development of effective shark repellents.

Animals↗
PubMed2005

Caudal fin allometry in the white shark Carcharodon carcharias: implications for locomotory performance and ecology.

Allometric scaling analysis was employed to investigate the consequences of size evolution on hydrodynamic performance and ecology in the white shark Carcharodon carcharias. Discriminant analysis using the power equation y=ax(b) was negative for caudal fin span (S) versus fork length (FL) in C. carcharias. In contrast in two delphinid species, Delphinus capensis and Tursiops aduncus, the span of the flukes versus fork length rises in positive allometric fashion, and strong positive allometry of S versus [corrected] radicalA (area) was also recorded. The latter reflects a high lift/drag ratio. S versus radicalA in C. carcharias displays negative allometry and consequently a lower lift/drag ratio. A lower aspect ratio (AR) caudal fin in C. carcharias compared to that of the delphinids (mean 3.33 and 4.1, respectively) and other thunniform swimmers provides the potential for better maneuverability and acceleration. The liver in sharks is frequently associated with a buoyancy function and was found to be positively allometric in C. carcharias. The overall findings suggest that the negatively allometric caudal fin morphometrics in C. carcharias are unlikely to have deleterious evolutionary fitness consequences for predation. On the contrary, when considered in the context of positive liver allometry in C. carcharias it is hereby suggested that buoyancy may play a dominant role in larger white sharks in permitting slow swimming while minimizing energy demands needed to prevent sinking. In contrast hydrodynamic lift is considered more important in smaller white sharks. Larger caudal fin spans and higher lift/drag ratio in smaller C. carcharias indicate greater potential for prolonged, intermediate swimming speeds and for feeding predominantly on fast-moving fish, in contrast to slow-swimming search patterns of larger individuals for predominantly large mammalian prey. Such data may provide some answers to the lifestyle and widespread habitat capabilities of this still largely mysterious animal.

Animal Structures↗
PubMed2002

Ultrastructure of basement membranes in developing shark tooth.

Based on studies of the tooth of largely mammalian species, the dental basement membranes are shown to be specialized for various roles significant in the development and maintenance of the tooth. Comparative studies with the nonmammalian tooth will facilitate further clarification of the mechanisms of mammalian tooth formation. In this study, basement membranes of the shark tooth in successive developmental stages was ultrastructurally examined for elucidation of their roles in odontogenesis. Teeth of a shark, Cephaloscyllium umbratile, were processed for thin section electron microscopy. Throughout the developmental stages the lamina densa of the basement membrane was made up of a fine network of "cords," irregular anastomosing strands known to be the major component of mammalian basement membranes. In the presecretory stage of the shark tooth, dental papilla cells were immobilized for their differentiation into odontoblasts by means of the binding of their processes to numerous narrow extensions of the lamina densa of the inner dental epithelium. In the secretory stage, a number of cords of the widened lamina densa were extended towards and bound to tubular vesicles of the forming enameloid. During the mineralization stage, fragments of the degrading enameloid matrix appeared to be moving through the lamina densa to the epithelial cells for processing. In the maturation stage, half of the lamina densa facing the enameloid was mineralized forming an advancing edge of mineralization of the enameloid. It provided strong binding and smooth transition of organic to mineral phase which may allow transportation of substances across the phases for enameloid maturation in a way similar to that reported in the mammalian tooth. These observations indicate that basement membranes of the developing shark tooth, as those in the mammalian tooth, play various roles, including anchoring, firm binding, and possible mediation of the transport of substances that are known to be vital for the development of the tooth.

Animals↗
PubMed2000

Congener-specific determination of polychlorinated biphenyls in shark and grouper livers from the northwest African Atlantic Ocean.

Concentrations of 24 individual PCB congeners have been measured in livers of groupers (Epinephelus marginatus) and eight shark species (Centroscymnus coelolepis, Centrophorus squamosus, Dalatias licha, Hydrolagus affinis, Deania profundorum, Centroscymnus cryptacanthus, Etmopterus princeps, Deania histricosa) collected between 1994 and 1995 from the northwest African Atlantic Ocean. The concentration range of the total PCBs was 39.4-4,723 ng/g (wet weight). The TEQs found were between 0.15 and 197 pg/g (wet weight). Analysis has revealed differences in PCB content and PCB profiles among the eight shark and grouper species. The location and depth at which the shark lives and the liver lipid content were related with their PCB liver concentrations. The PCB profiles were dominated by congeners 138 and 153, and among the most toxic congeners the order of abundance was PCB 77 > 126 > 169. Chiral PCBs 95, 132, 136, 149, and 174 were found to be racemic or nearly racemic in almost all the groupers (E. marginatus) studied. The PCB profiles of shark species and groupers were compared by principal component analysis. Samples were separated into groups according their trophic levels and geographical variations.

Analysis of Variance↗
PubMed2004

Infrastructure in the electric sense: admittance data from shark hydrogels.

Elasmobranchs (sharks, skates, and rays) possess an electrosensory system with an infrastructure of canals connecting the electrosensors to the environment. The electrosensors and canals are filled with a uniform hydrogel, but the gel's function has not yet been determined. We present electrical admittance spectra collected from the hydrogel from 0.05 to 100 kHz, covering the effective range of the electrosensors. We have taken samples of this gel, postmortem, from Triaenodon obesus and Carcharodon carcharias; for purposes of comparison, we have synthesized a series of collagen-based hydrogel samples. The shark hydrogels demonstrate suppressed admittance when compared to both seawater and collagen gels. In particular, collagen hydrogels with equivalent ion concentrations are roughly 2.5 times more polarizable than the shark samples. We conclude that the shark hydrogels strongly localize ionic species, and we discuss the implications for the related roles of the gel and the canals in the electric sense. The gel-filled canals appear better suited to fostering voltage differences along their length than to providing direct electrical contact to the seawater environment.

Animals↗
PubMed2004

Freshwater to seawater acclimation of juvenile bull sharks (Carcharhinus leucas): plasma osmolytes and Na+/K+-ATPase activity in gill, rectal gland, kidney and intestine.

This study examined the osmoregulatory status of the euryhaline elasmobranch Carcharhinus leucas acclimated to freshwater (FW) and seawater (SW). Juvenile C. leucas captured in FW (3 mOsm l(-1) kg(-1)) were acclimated to SW (980-1,000 mOsm l(-1) kg(-1)) over 16 days. A FW group was maintained in captivity over a similar time period. In FW, bull sharks were hyper-osmotic regulators, having a plasma osmolarity of 595 mOsm l(-1) kg(-1). In SW, bull sharks had significantly higher plasma osmolarities (940 mOsm l(-1) kg(-1)) than FW-acclimated animals and were slightly hypo-osmotic to the environment. Plasma Na(+), Cl(-), K(+), Mg(2+), Ca(2+), urea and trimethylamine oxide (TMAO) concentrations were all significantly higher in bull sharks acclimated to SW, with urea and TMAO showing the greatest increase. Gill, rectal gland, kidney and intestinal tissue were taken from animals acclimated to FW and SW and analysed for maximal Na(+)/K(+)-ATPase activity. Na(+)/K(+)-ATPase activity in the gills and intestine was less than 1 mmol Pi mg(-1) protein h(-1) and there was no difference in activity between FW- and SW-acclimated animals. In contrast Na(+)/K(+)-ATPase activity in the rectal gland and kidney were significantly higher than gill and intestine and showed significant differences between the FW- and SW-acclimated groups. In FW and SW, rectal gland Na(+)/K(+)-ATPase activity was 5.6+/-0.8 and 9.2+/-0.6 mmol Pi mg(-1) protein h(-1), respectively. Na(+)/K(+)-ATPase activity in the kidney of FW and SW acclimated animals was 8.4+/-1.1 and 3.3+/-1.1 Pi mg(-1) protein h(-1), respectively. Thus juvenile bull sharks have the osmoregulatory plasticity to acclimate to SW; their preference for the upper reaches of rivers where salinity is low is therefore likely to be for predator avoidance and/or increased food abundance rather than because of a physiological constraint.

Adaptation, Physiological↗
PubMed2004

Analysis of EphA4 in the lesser spotted catshark identifies a primitive gnathostome expression pattern and reveals co-option during evolution of shark-specific morphology.

The Eph family is the largest known group of structurally related receptor tyrosine kinases (RTKs). Each Eph receptor has a specific Ephrin ligand, and these function to define spatial boundaries during development. Analyses of EphA4 in mouse, chick, frog and zebrafish embryos have implicated this gene in a number of developmental processes, including maintenance of segmental boundaries, axon guidance, limb development, neural crest migration and patterning of the ear. In order to determine which components of EphA4 function may be primitive for gnathostomes, we cloned EphA4 from the lesser spotted catshark ( Scyliorhinus canicula) and examined its expression pattern during shark embryonic development. Consistent with the patterns reported for bony fish and tetrapods, we observed segmental expression of EphA4 in the developing hindbrain and later in the pharyngeal arches of shark embryos. EphA4 was also detected during sensory organogenesis, in the developing ear, eye, nasal pits and lateral line. A dynamic pattern of EphA4expression occurs during shark fin development, suggesting an early role in outgrowth and patterning of the fin buds and a later role in tissue differentiation. We also observed several novel domains of EphA4expression that have not been reported in other vertebrates, including external gill buds, dermal denticles, median fins and claspers. While some of these domains may reflect co-option of EphA4expression to novel sites for development of shark-specific characters, others are more likely to be ancestral patterns of expression that were lost in other vertebrate lineages.

Amino Acid Sequence↗
PubMed1985

Chemical nature of collagen in the placoid-scale dentine of the blue shark, Prionace glauca L.

The dentine fraction was obtained from powdered placoid scales by differential density-flotation, and demineralized with 0.5 M EDTA. Monomeric alpha 1 and alpha 2 chains of collagen were extracted from the residual organic matrix, and the two alpha chains purified by chromatography. The two alpha chains were also isolated from shark-skin collagen. The corresponding alpha chains from shark dentine and skin collagens resembled each other closely in chromatographic and electrophoretic behaviour and in their CNBr-peptide maps but differed from calf-skin alpha chains. The differences in the chemical composition between shark dentine and skin were due only to post-translational modification (hydroxylation and phosphorylation), indicating that the collagens are of the same type. The hydroxylation of prolyl and lysyl residues occurred more in the dentine alpha chains than in the skin chains. Among the four alpha chains, the phosphate content was the highest in the alpha 2 chain of the dentine collagen. These differences in hydroxylation and phosphorylation have been observed among alpha chains of mammalian mineralized and unmineralized tissues. The preferential dimerization to form alpha 1-alpha 2, characteristic of shark-skin collagen, was not observed in the dentine collagen. Other dimers were hardly detectable in the latter.

Animals↗
PubMed1992

Crystal structure of the unique parvalbumin component from muscle of the leopard shark (Triakis semifasciata). The first X-ray study of an alpha-parvalbumin.

The three-dimensional structure of parvalbumin from leopard shark (Triakis semifasciata) with 109 amino acid residues (alpha-series) is described at 1.54 A resolution. Crystals were grown at 20 degrees C from 2.9 M-potassium/sodium phosphate solutions at pH 5.6. The space group is P3(1)21 and unit cell dimensions are a = b = 32.12 A and c = 149.0 A. The structure has been solved by the molecular replacement method using pike 4.10 parvalbumin as a model. The final structure refinement resulted in an R-factor of 17.3% for 11,363 independent reflections at 1.54 A resolution. The shark parvalbumin shows the main features of all parvalbumins: the folding of the chain including six alpha-helices, the salt bridge between Arg75 and Glu81, and the hydrophobic core. Compared to the structure of beta-parvalbumins from pike and carp, one main difference is observed: the chain is one residue longer and this additional residue, which extends the F helix, is involved through its C-terminal carboxylate group in a network of electrostatic contacts with two basic residues, His31 in the B helix and Lys36 in the BC segment. Furthermore, hydrogen bonds exist between the side-chains of Gln108 (F helix) and Tyr26 (B helix). There is therefore a "locking" of the tertiary structure through contacts between two sequentially distant regions in the protein and this is likely to contribute to making the stability of an alpha-parvalbumin higher in comparison to that of a beta-parvalbumin. The lengthening of the C-terminal F helix by one residue appears to be a major feature of alpha-parvalbumins in general, owing to the homologies of the amino acid sequences. Besides the lengthening of the C-terminal helix, the classification of the leopard shark parvalbumin in the alpha-series rests upon the observation of Lys13, Leu32, Glu61 and Val66. As this is the first crystal structure description of a parvalbumin from the alpha-phylogenetic lineage, it was hoped that it would clearly determine the presence or absence of a third cation binding site in parvalbumins belonging to the alpha-lineage. In beta-pike pI 4.10 parvalbumin, Asp61 participates as a direct ligand of a third site, the satellite of the CD site. In shark parvalbumin, as in nearly all alpha-parvalbumins, one finds Glu at position 61. Unfortunately, the conformation of the polar head of Glu61 cannot be inferred from the X-ray data.(ABSTRACT TRUNCATED AT 400 WORDS)

Amino Acid Sequence↗
PubMedDate not supplied

Functional equivalence of monomeric (shark) and dimeric (bovine) cytochrome c oxidase.

Cytochrome c oxidase isolated from hammerhead shark red muscle is monomeric in relation to the dimeric form of isolated bovine cytochrome c oxidase but in other ways bears a close resemblance to the enzyme isolated from mammalian tissue [1, 2]. Comparative studies of shark and bovine cytochrome c oxidase were extended to address the degree of functional similarity between the monomeric (shark) and dimeric (bovine) enzymes in the kinetics of peroxide binding and in the extent to which the catalytic action of the enzymes in vesicles can establish a proton gradient. Although the kinetics of peroxide binding and the proton pumping processes are complex, the dimeric and monomeric forms are quite similar with respect to these functional attributes. The kinetic heterogeneity of the process of peroxide binding is expressed in the shark enzyme as well as in the bovine enzyme, and both types of enzymes in vesicles can generate transmembrane proton gradients. On this basis we conclude that the dimeric state of isolated cytochrome c oxidase from mammalian sources is not essential for its function in vitro.

Animals↗