Photoaffinity labeling of the adenine binding site of the lectins from lima bean, Phaseolus lunatus, and the kidney bean, Phaseolus vulgaris

8-Azidoadenine was employed as a photoaffinity probe of the adenine binding site of the seed lectin from lima beans and from Phaseolus vulgaris erythroagglutinin. This compound was shown to (a) bind competitively to the adenine binding site of these lectins and (b) exhibit enhanced binding in the presence of 1,8-anilinonaphthalenesulfonic acid in the same manner as adenine. The presence or absence of 1,8-anilinonaphthalenesulfonic acid during labeling caused no change in the peptide maps of either lectin when digested with trypsin. The peptide maps of each lectin showed one major peak of radioactivity. Sequencing of the corresponding tryptic peptide from lima bean lectin indicated the primary structure to be Val-Leu-Ile-Thr-Tyr-Asp-Ser-Ser-Thr-Lys. The sequence of the labeled peptide isolated from P. vulgaris erythroagglutinin was Thr-Thr-Thr-Trp-Asp-Phe-Val-Gly-Glu-Asn-Glu-Val-Leu-Ile-Thr-Tyr, which corresponded to residues 173-190 of the cDNA-derived sequence (Hoffman, L. M., and Donaldson, D. D. (1985) EMBO J. 4, 883-889). Residues 186-190 (italicized) are identical to the first five amino acids in the lima bean lectin peptide. The peptides are located at the COOH-terminal half of the lectin and show extensive homology with other legume lectins.     

Thymosin fraction 5 (TF5) stimulates secretion of adrenocorticotropic hormone (ACTH) from cultured rat pituitaries

In vivo administration of a partially purified thymic hormone-containing extract of the thymus gland, TF5, causes an increase in serum glucocorticoids. The lack of a direct effect of TF5 on adrenal corticosterone secretion suggests that it is mediated at the level of the pituitary. Cultured rat pituitary monolayers were used to determine if the effect is mediated by stimulation of ACTH secretion from the pituitary. Two lots of TF5, BPP100 and C114080-01, caused a dose dependent secretion of ACTH from cultured pituitary monolayers. There was a synergistic effect when the cells were treated with both TF5 and corticotropin-releasing factor (CRF). Immunoneutralization studies were done in which the cells were treated with TF5 or CRF and an antibody to CRF. The antibody completely blocked CRF induced ACTH release, but had no effect on TF5 stimulated ACTH release, suggesting that the activity is not due to a CRF-like peptide in TF5. A number of peptides isolated from TF5, and certain other peptides produced by the immune system were evaluated for their ability to stimulate ACTH secretion. These included thymosin (TSN) alpha 1, alpha 11, and beta 4, prothymosin alpha (PT alpha, thymopoeitin 5 (TP5), factuer thymique serique (FTS), interferon alpha (INF alpha), INF gamma, interleukin 1 (IL-1), and interleukin 2 (IL-2). None of these factors had any effect on pituitary ACTH secretion. These results demonstrate that some peptide component of TF5 causes an increase in serum corticosteroids by stimulating pituitary ACTH release.     

Motility of the spirochete Leptospira

Spirochetes are a group of bacteria with a unique ultrastructure and a fascinating swimming behavior. This article reviews the hydrodynamics of spirochete motility, and examines the motility of the spirochete Leptospira in detail. Models of Leptospira motility are discussed, and future experiments are proposed. The outermost structure of Leptospira is a membrane sheath, and within this sheath are a helically shaped cell cylinder and two periplasmic flagella. One periplasmic flagellum is attached subterminally at either end of the cell cylinder and extends partway down the length of the cell. In swimming cells, each end of the cell may assume either a spiral or a hook shape. Translational cells have the anterior end spiral shaped, and the posterior end hook shaped. In the model of Berg et al., the periplasmic flagella are believed to rotate between the sheath and the cell cylinder. Rotation of the anterior periplasmic flagellum causes the generation of a gyrating spiral-shaped wave. This wave is believed sufficient to propel the cells forward in a low-viscosity medium. The cell cylinder concomitantly rolls around the periplasmic flagella in the opposite direction--which allows the cell to literally screw through a gel-like viscous medium without slippage. This model is presented, and it is contrasted to previous models of Leptospira motility.     

What is Unique About Superoxide Toxicity as Compared to Other Biological Reductants? — A Hypothesis

Usually the toxicity of superoxide is attributed lo its ability to reduce metal ions and subsequently reoxidation of the metal by hydrogen peroxide yields deleterious oxidizing species. As many other nontoxic biological reductants reduce metal compounds, we suggest that part of the mechanism of superoxide toxicity results from its ability to oxidize metal ions bound to biological targets, which subsequently degrade the target via an intramolecular electron Transfer reaction.     

Transthyretin Pro55, a variant associated with early-onset,aggressive, diffuse amyloidosis with cardiac and neurologic involvement

Summary Mutations in the protein transthyretin cause amyloidosis involving the heart, peripheral nerves, and other organs. A family from West Virginia developed an unusually aggressive form of widespread transthyretin amyloidosis. Single-strand conformation polymorphism analysis revealed a variant in the transthyretin gene, which was found on sequencing to be a TC transversion at position 2 of codon 55, corresponding to a Leu Pro substitution. The variant sequence was confirmed by restriction analysis and polymerase chain reaction (PCR)-primer introduced restriction analysis.     

Changes in Osmotic Pressure and Mucilage during Low-Temperature Acclimation of Opuntia ficus-indica

Opuntia ficus-indica, a Crassulacean acid metabolism plant cultivated for its fruits and cladodes, was used to examine chemical and physiological events accompanying low-temperature acclimation. Changes in osmotic pressure, water content, low molecular weight solutes, and extracellular mucilage were monitored in the photosynthetic chlorenchyma and the water-storage parenchyma when plants maintained at day/night air temperatures of 30/20°C were shifted to 10/0°C. An increase in osmotic pressure of 0.13 megapascal occurred after 13 days at 10/0°C. Synthesis of glucose, fructose, and glycerol accounted for most of the observed increase in osmotic pressure during the low-temperature acclimation. Extracellular mucilage and the relative apoplastic water content increased by 24 and 10%, respectively, during exposure to low temperatures. These increases apparently favor the extracellular nucleation of ice closer to the equilibrium freezing temperature for plants at 10/0°C, which could make the cellular dehydration more gradual and less damaging. Nuclear magnetic resonance studies helped elucidate the cellular processes during ice formation, such as those revealed by changes in the relaxation times of two water fractions in the chlorenchyma. The latter results suggested a restricted mobility of intracellular water and an increased mobility of extracellular water for plants at 10/0°C compared with those at 30/20°C. Increased mobility of extracellular water could facilitate extracellular ice growth and thus delay the potentially lethal intracellular freezing during low-temperature acclimation.     

A semiempirical study of the prototropic tautomerism of hypoxanthine

The total and relative energies, bond order matrices and localized MOs for the eight possible tautomers of hypoxanthine (HYP) have been calculated, with full geometry optimization, using both AM1 and MNDO methods. The AM1 relative energies show that HYP(9,1), HYP(7,1) and HYP (9,10) are the predominant species at room temperature, the two former being in larger concentration that the latter. The calculated IR spectra for these species agree well with the reported spectrum in an isolated matrix, which has been interpreted in terms of the presence of these three tautomeric forms. The MNDO method does not predict the right order, and the more stable tautomer would be HYP(9,10). The calculated structure for the HYP(9,1) species shows that the molecule is essentially planar. The bond distances compare well with those of hypoxanthine hydrochloride and guanine and also correlate well with the calculated bond orders. The proton affinities for the three more stable tautomers have also been calculated. For HYP(9,1) the prefered site of protonation is N7, whereas for HYP(7,1) the protonation occurs rather at N9. These results agree well with¹⁵N and¹³C NMR studies in DMSO.     

Determination of epithelial half-somites in skeletal morphogenesis.

The segmental body plan of vertebrates arises from the metameric organization of the paraxial mesoderm into somites. Each mesodermal somite is subdivided into at least two distinct domains: rostral and caudal. The segmental pattern of dorsal root ganglia, sympathetic ganglia and nerves is imposed by differential properties of either somitic domain. In the present work, we have extended these studies by investigating the contribution of rostral or caudal-half somites to vertebral development using grafts of multiple somite halves. In both rostral and caudal somitic implants, the grafted mesoderm dissociates normally into sclerotome and dermomyotome, and the sclerotome further develops into vertebrae. However, the morphogenetic capabilities of each somitic half differ. The pedicle of the vertebral arch is almost continuous in caudal half-somite grafts and is virtually absent in rostral half-somite implants. Similarly, the intervertebral disk is present in rostral half-somite chimeras, and much reduced or virtually absent in caudal somite chimeras. Thus, only the caudal half cells are committed to give rise to the vertebral pedicle, and only the rostral half cells are committed to give rise to the fibrocartilage of the intervertebral disk. Each vertebra is therefore composed of a pedicle-containing area, apparently formed by the caudal half-somite, followed by a pedicle-free zone, the intervertebral foramen, derived from the rostral somite. These data directly support the hypothesis of resegmentation, in which vertebrae arise by fusion of the caudal and rostral halves of two consecutive somites.     

Human mast cell proteases hydrolyze neurotensin, kinetensin and Leu5-enkephalin.

Purified mast cell carboxypeptidase cleaved the C-terminal leucines from Leu5-enkephalin (Leu-ENK), neurotensin (NT), and kinetensin (KT), with Km values of 36, 16, and 15 microM, and kcat values of 44, 51, and 53 s-1, respectively. To better predict potential in vivo hydrolysis products generated by mast cell proteases, these peptides were incubated with released skin mast cell supernatants. Leu5-enkephalin was hydrolyzed only by carboxypeptidase. Kinetensin was cleaved by tryptase, chymase, and carboxypeptidase to yield KT(1-3), KT(1-7), KT(1-8), KT(4-7), and KT(4-8), the last two peptides by the concerted action of two of the proteases. NT(1-11) and NT(1-12) were generated from neurotensin by chymase and carboxypeptidase, respectively.     

Distribution of opioidergic,sympathetic and neuropeptide Y-positive nerves in the sphincter of Oddi and biliary tree of the monkey,Macaca fascicularis

Summary The opioidergic, sympathetic and neuropeptide Y-positive innervation of the sphincter of Oddi (common bile duct sphincter and pancreatic duct sphincter), as well as other segments of the extrahepatic biliary tree was studied in the monkey by use of immunohistochemistry. Methionine-enkephalin-positive nerves were seen to innervate the smooth muscle of all portions of the sphincter of Oddi and also local ganglion cells. No methionine-enkephalin-positive nerves could be detected in the common bile duct, pancreatic duct or gallbladder. Tyrosine hydroxylase-positive nerves occurred between smooth muscle bundles and also ran to local ganglion cells as well as along the common bile duct. Neuropeptide Y-positive nerves were observed within smooth muscle of the sphincter of Oddi (all portions), common bile duct, pancreatic duct and gallbladder. No evidence of any differential innervation of the pancreatic duct and common bile duct sphincters could be detected with these markers.