Topsy-turvy: turning the counter-current heat exchange of leatherback turtles upside down

Counter-current heat exchangers associated with appendages of endotherms feature bundles of closely applied arteriovenous vessels. The accepted paradigm is that heat from warm arterial blood travelling into the appendage crosses into cool venous blood returning to the body. High core temperature is maintained, but the appendage functions at low temperature. Leatherback turtles have elevated core temperatures in cold seawater and arteriovenous plexuses at the roots of all four limbs. We demonstrate that plexuses of the hindlimbs are situated wholly within the hip musculature, and that, at the distal ends of the plexuses, most blood vessels supply or drain the hip muscles, with little distal vascular supply to, or drainage from the limb blades. Venous blood entering a plexus will therefore be drained from active locomotory muscles that are overlaid by thick blubber when the adults are foraging in cold temperate waters. Plexuses maintain high limb muscle temperature and avoid excessive loss of heat to the core, the reverse of the accepted paradigm. Plexuses protect the core from overheating generated by muscular thermogenesis during nesting.     

A RAPD study of the Sarcostemma group of Cynanchum (Apocynaceae-Asclepiadoideae-Asclepiadeae)

One hundred and thirty-seven accessions of Cynanchum viminale and its relatives, formerly known as Sarcostemma, were studied using randomly amplified polymorphic DNA (RAPD). A fingerprinting technique was used because sequencing had failed to differentiate between morphologically separable groups. Chromosome counts were conducted to establish the ploidy level of the accessions. The banding patterns resulting from RAPD analysis were evaluated with Canonical Analysis of Principal Coordinates, Permanova and neighbour-joining. A strong geographic component was found in the structure of the group. Taxa considered species or subspecies based on morphology often formed coherent groups. The data are interpreted to reflect at least two cycles of diversification: the first one from Madagascar and the second one most likely from the East African–Arabian region, reaching Madagascar again. In mainland Africa, polyploidisation has occurred several times.     

Carettacola hawaiiensis n. sp. (Trematoda: Spirorchidae) from the green turtle, Chelonia mydas, in Hawaii.

Carettacola hawaiiensis n. sp. (Trematoda: Spirorchidae) is described from the hepatic vessels of the green turtle, Chelonia mydas (L.), in Hawaii. The new species differs from any previously described species of Carettacola in size, placement of vitellaria, and shape and placement of Laurer's canal. The genus Haemoxenicon Martin and Bamberger, 1952, becomes a synonym of Carettacola Manter and Larson, 1950. Haemoxenicon stunkardi Martin and Bamberger, 1952, is transferred to the genus Carettacola Manter and Larson, 1950, and becomes Carettacola stunkardi n. comb. An emended generic diagnosis for Carettacola is given along with a key to the species.     

Characterization of an S-layer glycoprotein produced in the course of S-layer variation of<Emphasis Type="Italic"> Bacillus stearothermophilu</Emphasis>s ATCC 12980 and sequencing and cloning of the<Emphasis Type="Italic"> sbsD</Emphasis> gene encoding the protein moiety

The cell surface of Bacillus stearothermophilus ATCC 12980 is completely covered by an oblique lattice which consists of the S-layer protein SbsC. On SDS-polyacrylamide gels, the mature S-layer protein migrates as a single band with an apparent molecular mass of 122 kDa. During cultivation of B. stearothermophilus ATCC 12980 at 67 degrees C instead of 55 degrees C, a variant developed that had a secondary cell wall polymer identical to that of the wild-type strain, but it carried an S-layer glycoprotein that could be separated on SDS-polyacrylamide gels into four bands with apparent molecular masses of 92, 118, 150 and 175 kDa. After deglycosylation, only a single protein band with a molecular mass of 92 kDa remained. The complete nucleotide sequence encoding the protein moiety of this S-layer glycoprotein, termed SbsD, was established by PCR and inverse PCR. The sbsD gene of 2,709 bp is predicted to encode a protein of 96.2 kDa with a 30-amino-acid signal peptide. Within the 807 bp encoding the signal peptide and the N-terminal sequence (amino acids 31-269), different nucleotides for sbsD and sbsC were observed in 46 positions, but 70% of these mutations were silent, thus leading to a level of identity of 95% for the N-terminal parts. The level of identity of the remaining parts of SbsD and SbsC was below 10%, indicating that the lysine-, tyrosine- and arginine-rich N-terminal region in combination with a distinct type of secondary cell wall polymer remained conserved upon S-layer variation. The sbsD sequence encoding the mature S-layer protein cloned into the pET28a vector led to stable expression in Escherichia coli HMS174(DE3). This is the first example demonstrating that S-layer variation leads to the synthesis of an S-layer glycoprotein.     

Kinetics of irreversible dissociation for proteins bound cooperatively to DNA

We consider the irreversible dissociation kinetics of proteins that bind cooperatively and nonspecifically to DNA. Our model consists of an infinitely long one-dimensional nucleic acid lattice on which are bound protein ligands. A set of adjacent bound proteins forms a cluster of length n. A protein molecule may dissociate from any site within the bound cluster, not only from the ends, as was assumed in a previous model of this process due to Lohman [(1983) Biopolymers 22 , 1697–1713]. By considering this additional pathway, we present a more general treatment of the dissociation kinetics of cooperatively bound ligands. We show that dissociation from the (n?2) internal positions of an n-cluster is an important pathway when the initial fractional saturation of the lattice is close to unity and the co operatively is low. When the fractional saturation is initially equal to 1 and the co operatively is low, our model does not give the zero-order dissociation kinetics predicted by the Lohman model.