Oxytocin and an oxytocin agonist administered centrally decrease food intake in rats.

Intracerebroventricular administration of oxytocin (OT) and an OT agonist significantly decreased food intake in a dose-related manner in fasted rats. Central administration of an OT antagonist by itself (up to doses of 8 nmol) did not potentiate deprivation-induced food intake, but pretreatment with the OT receptor antagonist prevented the expected inhibition of food intake produced by OT and the OT agonist. Once-daily ICV injections of OT led to the development of tolerance to the inhibitory effects on food intake by the third day of treatment, but daily pretreatment with the OT antagonist prevented the development of this tolerance. In addition to causing decreased food intake, ICV administration of OT significantly increased grooming behavior but produced no dyskinesias. The inhibitory effect of OT on food intake was characterized by decreased amounts of food intake but a normal pattern of ingestion. The anorexia produced was central in nature and was not associated with altered plasma levels of hormones involved in caloric homeostasis or with changes in blood glucose. The OT agonist had relatively little effect on water intake when given in doses that significantly inhibited food intake. These results support the hypothesis that specific OT receptors within the central nervous system participate in the inhibition of feeding under certain conditions in rats.     

Thermodynamic analysis of the lactose repressor-operator DNA interaction

Kinetic and equilibrium constants for lactose repressor-operator DNA interaction have been examined as a function of salt concentration, size and sequence context of the operator DNA, and temperature. Significant salt effects were observed on kinetic and equilibrium parameters for pLA 322-8, an operator-containing derivative of pBR 322, and pIQ, an operator and pseudooperator-containing derivative of pBR 322. The association rate constant and equilibrium constant for the 40 base pair operator fragment were also salt dependent. Data for all the DNAs were consistent with a sliding mechanism for repressor-operator association/dissociation [Berg, O. G., & Blomberg, C. (1978) Biophys. Chem. 8, 271-280]. Calculation of the number of ionic interactions based on salt dependence yielded a value of approximately 8 for repressor binding to pIQ and pLA 322-8 vs. approximately 6 for the repressor-40 base pair fragment. These data and the differences in binding parameters for the plasmids vs. the 40 base pair operator are consistent with the formation of an intramolecular ternary complex in the plasmid DNAs. Unusual biphasic temperature dependence was observed in the equilibrium and dissociation rate constants for pLA 322-8, pIQ, and the 40 base pair fragment. These observations coupled with a discontinuity found in the inducer association rate constant as a function of temperature suggest a structural change in the protein. The large positive entropy contributions associated with repressor binding to all the DNAs examined provide the significant driving force for the reaction and are consistent with involvement of ionic and apolar interactions in complex formation.     

Heparin and ionic strength-dependent conversion of antithrombin III from an inhibitor to a substrate of alpha-thrombin

The stoichiometry of antithrombin III (AT) inhibition of alpha-thrombin (T) has been investigated in the presence and absence of heparin as a function of ionic strength by quantitative titration of enzyme active sites. In contrast to the ionic strength-independent stoichiometry of 1.0 mol of AT/mol of T observed in the absence of heparin, the presence of high-affinity heparin (HAH) resulted in an ionic strength-dependent increase in the apparent stoichiometry of inhibition from a molar ratio of 1.1 AT/T at an ionic strength of 0.3 to 9.8 mol of AT/T when the ionic strength was lowered to 0.01. Reduced sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the reaction products revealed that the increased AT/T stoichiometry was due to preferential formation of a specific proteolytically cleaved form of AT that was indistinguishable from the previously characterized reactive site-cleaved AT (ATM). Using high-performance liquid chromatography and sodium dodecyl sulfate-polyacrylamide gel electrophoresis to quantitate ATM, the cleaved inhibitor was shown to be formed rapidly and concomitant with the stable thrombin-antithrombin complex (TAT) and quantitatively accounted for the apparent increase in reaction stoichiometry at low ionic strength in the presence of HAH. The levels of HAH required to produce maximum ATM were catalytic at mu greater than or equal to 0.15, but became stoichiometric as the ionic strength decreased below 0.1. Substantially less ATM was produced in the presence of low-affinity heparin, while a low molecular weight HAH, virtually inactive in accelerating T inhibition by AT, was unable to promote significant ATM formation. These results indicate competition between substrate and inhibition reactions of AT with T which are affected by an ionic strength-dependent heparin interaction. A reaction mechanism accounting for these observations is proposed.     

The stimulation of hepatic gluconeogenesis by acetoacetate precursors. A role for the monocarboxylate translocator

The regulation of the gluconeogenic pathway from the 3-carbon precursors pyruvate, lactate, and alanine was investigated in the isolated perfused rat liver. Using pyruvate (less than 1 mM), lactate, or alanine as the gluconeogenic precursor, infusion of the acetoacetate precursors oleate, acetate, or beta-hydroxybutyrate stimulated the rate of glucose production and, in the case of pyruvate (less than 1 mM), the rate of pyruvate decarboxylation. alpha-Cyanocinnamate, an inhibitor of the monocarboxylate transporter, prevented the stimulation of pyruvate decarboxylation and glucose production due to acetate infusion. With lactate as the gluconeogenic precursor, acetate infusion in the presence of L-carnitine stimulated the rate of gluconeogenesis (100%) and ketogenesis (60%) without altering the tissue acetyl-CoA level usually considered a requisite for the stimulation of gluconeogenesis by fatty acids. Hence, our studies suggest that gluconeogenesis from pyruvate or other substrates which are converted to pyruvate prior to glucose synthesis may be limited or controlled by the rate of entry of pyruvate into the mitochondrial compartment on the monocarboxylate translocator.     

Mutagen sensitivity of Neurospora meiotic mutants

The Neurospora meiotic mutants, mei-1, mei-2, mei-3, and mei-4 were tested for cross sensitivity to mutagens. Mei-2 and mei-3 are sensitive to MMS, gamma-irradiation and histidine. Mei-2 is not sensitive to ultraviolet (UV) at 20 degrees C. Tests with recombinants with crossovers to either side of mei-2 or mei-3 show that these traits are the pleiotropic properties of a single gene which also determines meiotic behavior. The mei-2 gene maps to the right of al-3 on linkage group V. It is not allelic to mus-11. Upon backcrossing, the originally dominant meiotic effect of mei-2 becomes recessive to partially dominant. The histidine sensitivity is recessive.     

Structure of tomato busy stunt virus IV. The virus particle at 2.9 A resolution

The structure of tomato bushy stunt virus has been determined crystallographically to 2.9 A resolution. Details are presented of both the molecular structure and the methods by which it has been solved. The icosahedrally symmetric viral shell is composed of 180 protein subunits (Mr 43,000), with three similar but distinct modes of subunit bonding. This capacity for alternative packing is due to localized flexibility in the folded polypeptide (hinges between domains) and to multiple conformations for surface side-chains. The polypeptide backbone has an essentially invariant fold within a compact domain. A mechanism for correct positioning of the different modes of subunit interaction is evident from the structure of the TBSV particle. Thirty-five residues of the polypeptide chain fold in an ordered way on 60 of the 180 subunits, forming an internal framework. Interaction of folded domains with this framework permits accuracy of long-range geometry (correct curvature and closure) to be determined by unambiguous switching between alternative local contact angles. RNA packs tightly into the particle interior. Protein-RNA interactions occur through parts of the subunit that are flexibly linked to the well-ordered domains of the shell. This variable interaction imposes minimum restrictions on the folding of the RNA chain.     

Ultrastructural evidence for the biflagellate origin of the uniflagellate fungal zoospore

Summary The morphological similarities between the kinetosome and the second centriole of the zoospores of Phlyctochytrium kniepii and P. punctatum (Chytridiomycetes) suggest that the second centriole in the chytrid zoospore is a vestigial flagellum base. It is suggested that the term vestigial kinetosome may also be used when referring to the structure which is presently termed the second centriole of the chytrid zoospore. Morphological similarities between the chytrid zoospores of P. kniepii and P. punctatum and the zoospores of Rhizidiomyces apophysatus (Hyphochytridiomycetes) are noted. The possible biflagellate origin of fungi with uniflagellate zoospores is discussed. The third fiber (C fiber) of the kinetosome triplet is shown to form as an outgrowth of the B fiber of the kinetosome doublet.     

Vulnerability to predation and physiological stress responses of experimentally descaled juvenile chinook salmon,Oncorhynchus tshawytscha

Synopsis Juvenile salmonids,Oncorhynchus spp., commonly encounter conditions (e.g., during hatchery release and dam passage) that result in damage to the skin, scale, and slime complex. We conducted laboratory experiments to determine if descaling of juvenile chinook salmon,O. tshawytscha, increased their vulnerability to predation, and to assess the physiological stress responses elicited by descaling. Salmon were experimentally descaled on either 10% or 20% of their total body area. When offered equal numbers of control and descaled juvenile chinook salmon, northern squawfish,Ptychocheilus oregonensis, did not consume significantly more of either prey type (48–60% of consumed prey were descaled). Juvenile chinook salmon descaled on 10% of their body area did show significant physiological stress responses, however. Mean concentrations of plasma cortisol peaked 1 h after descaling, and returned to control levels by 12 h. Plasma glucose peaked 3 h post-treatment and remained elevated for 24 h. Plasma lactate increased immediately following treatment and returned to undisturbed control levels by 3 h. The osmoregulatory response of plasma potassium was highly variable, but plasma sodium decreased immediately and remained low for 24 h. The observed physiological responses suggest that descaling of juvenile chinook salmon could result in decreased resistance to disease and other stressors encountered in the field, possibly leading to reduced performance capacity and lowered survival.