Diel plasma melatonin profile in a cyclostome, the river lamprey

Plasma melatonin levels in adult river lampreys Lampetra fluviatilis , sampled during their upstream migration showed a pronounced diel profile, with high levels during the night and lower levels during the day, showing that a cyclostome, in common with other vertebrates, exhibits such a diel plasma profile.     

Direct branch of external carotid: a masseteric artery

An additional branch of the right external carotid in the form of an unusual direct artery to m. masseter is described. It arose as a terminal branch along with the maxillary and superficial temporal arteries, ran in the substance of the parotid gland to supply the muscle on its lateral aspect. The pertinent anatomical literature is reviewed.     

A synthetic peptide encompassing the binding site of the second zinc atom (the 'structural' zinc) of alcohol dehydrogenase.

A 23-residue peptide was synthesized that incorporates the loop which binds the structural zinc atom of mammalian alcohol dehydrogenases and contributes, in part, to subunit interactions in the native enzyme. Neither the amino acid composition nor the sequence of the peptide resemble those of zinc fingers. The reduced peptide stoichiometrically binds zinc or cobalt to form stable complexes with a dissociation constant of the peptide/CO2+ complex of 2.1 microM at pH 7.5. EDTA disrupts the complex. The absorption and magnetic circular dichroic spectra of the cobalt-peptide are indicative of a tetrahedral coordination geometry, and are similar to those of the cobalt-substituted structural site of horse and human (beta 1 beta 1) liver alcohol dehydrogenases. Consequently, the synthetic peptide can serve as a model for the metal-binding segment of alcohol dehydrogenase and for studies of fundamental problems concerning protein/metal interactions.     

Properties of a rat liver smooth microsomal subfraction not aggregated by Mg2+

A smooth microsomal fraction (smooth II microsomes) was earlier isolated and characterized in a number of investigations. Using a three-layer discontinuous sucrose gradient containing Mg²⁺ this fraction was divided into two subfractions (IIa and IIb) by a single centrifugation. The smooth IIa fraction proved to be a purified smooth microsomal fraction of specific composition. It contains high amounts of cytochromes $\text{b}{}_5$ and P-450, low activities of other electron transport enzymes and glucose-6-phosphatase, and no UDP-glucuronic acid transferase. No membrane or enzyme synthesis is induced in this subfraction by treatment with phenobarbital or methylcholanthrene. It appears that the membranes of smooth IIa microsomes derive from the smooth endoplasmic reticulum and are devoted to specific functions.     

Aging of the hypothalamo-pituitary-ovarian axis: hormonal influences and cellular mechanisms

Longitudinal studies employing heterochronic ovarian grafts and long-term ovariectomy indicate that there is no single pacemaker of reproductive aging. Neuroendocrine dysfunction, the declining follicular reserve, and ovarian secretions all contribute to reproductive decline, and their relative importance to the different stages of reproductive aging varies markedly. Moreover, although ovarian secretions during adulthood potentiate certain aspects of the reproductive aging process, their behavior does not fit a simple model of cumulative steroidal damage incurred over the lifespan. Current data are more consistent with temporally distinct windows of steroidal vulnerability for the events affected: cycle lengthening is affected by ovarian secretions during the period of cyclicity, and post-cyclic neuroendocrine failure is potentiated by ovarian secretions during the peri- and post-cyclic period of the lifespan. Recent examination of estradiol receptor dynamics reveals multiple, albeit selective, changes during aging that may contribute to the age-related impairments of tissue sensitivity to estrogen. These changes vary qualitatively and quantitatively among target tissues. Thus, aging of the hypothalamo-pituitary-ovarian axis at the cellular level mirrors, in its multifactorial nature, aging at the organismic level.     

TheGunnera symbiosis: DNA restriction fragment length polymorphism and protein comparisons ofNostoc symbionts

Cyanobacteria separated from symbiosis with several species of the angiospermGunnera were comparatively characterized and correlated with the locales and taxonomy of their host plants. All were identified as strains ofNostoc. Protein profiles and DNA restriction fragment length polymorphisms (from hybridizations with heterologousnifH andglnA probes) determined that three of the four cyanobacteria fromGunnera grown at one site in Sweden, each from a different host species, were very similar or identical. Plants of one species,G. manicata, grown in a second location at the site were infected with a different cyanobiont. Among five isolates from two species ofGunnera, collected in the same locale in New Zealand, three subgroups were documented. Isolates from three differentGunnera species grown in separate locations in the United States were each uniquely different. None of the cyanobacteria differed in the molecular weights of their glutamine synthetase and Fe-nitrogenase proteins. The diversity and accessibility of compatibleNostoc populations present in the soil micro-environment, not a critical selective factor required byGunnera, were concluded to be a major determinant in symbiont selection.