Comparison of goose-type, chicken-type, and phage-type lysozymes illustrates the changes that occur in both amino acid sequence and three-dimensional structure during evolution

The three-dimensional structure of goose-type lysozyme (GEWL), determined by x-ray crystallography and refined at high resolution, has similarities to the structures of hen (chicken) egg-white lysozyme (HEWL) and bacteriophage T4 lysozyme (T4L). The nature of the structural correspondence suggests that all three classes of lysozyme diverged from a common evolutionary precursor, even though their amino acid sequences appear to be unrelated (Grütter et al. 1983). In this paper we make detailed comparisons of goose-type, chicken-type, and phage-type lysozymes. The lysozymes have undergone conformational changes at both the global and the local level. As in the globins, there are corresponding alpha-helices that have rigid-body displacements relative to each other, but in some cases corresponding helices have increased or decreased in length, and in other cases there are helices in one structure that have no counterpart in another. Independent of the overall structural correspondence among the three lysozyme backbones is another, distinct correspondence between a set of three consecutive alpha-helices in GEWL and three consecutive alpha-helices in T4L. This structural correspondence could be due, in part, to a common energetically favorable contact between the first and the third helices. There are similarities in the active sites of the three lysozymes, but also one striking difference. Glu 73 (GEWL) spatially corresponds to Glu 35 (HEWL) and to Glu 11 (T4L). On the other hand, there are two aspartates in the GEWL active site, Asp 86 and Asp 97, neither of which corresponds exactly to Asp 52 (HEWL) or Asp 20 (T4L). (The discrepancy in the location of the carboxyl groups is about 10 A for Asp 86 and 4 A for Asp 97.) This lack of structural correspondence may reflect some differences in the mechanisms of action of the three lysozymes. When the amino acid sequences of the three lysozyme types are aligned according to their structural correspondence, there is still no apparent relationship between the sequences except for possible weak matching in the vicinity of the active sites.     

Mutants ofStreptomyces hygroscopicus deregulated in amylase and α-glucosidase formation

Summary Two mutants, M36 and M39, of turimycin-producingS. hygroscopicus JA 6599/PR1 obtained by directed selection in a chemostat displayed altered pattern of amylase and -glucosidase production as revelaed by both constitutive enzyme formation and higher enzyme levels.     

Localization of the neuronal cell adhesion molecule D2-protein in explant cultures of dorsal root ganglia by use of the colloidal-gold immunocytochemical technique

Summary The localization of the neuronal cell adhesion molecule (N-CAM), D2-protein, in explant cultures of rat dorsal root ganglia was investigated at the electron microscope level by the use of 17-nm-diameter colloidal gold particles coated with swine anti-rabbit immunoglobulin molecules. The minimum amount of IgG needed to coat the gold particles and the pH optimal for coating were both determined. Immunocytochemical studies of cultures revealed the binding of gold particles to the neuronal plasma membrane, especially on neuritic processes. Schwann cells were not labeled, and the level of unspecific background staining was very low.     

Production estimates of the benthic invertebrate community in a small Danish stream

Quantitative samples were used to investigate density, biomass and annual production of the benthic invertebrate fauna in a small Danish stream. Forty-eight taxa were found and the total invertebrate densities varied from 3 810 m^?2 in July to 20 040 m^?2 in December. The total mean annual biomass of the invertebrate fauna was 6.1 g ash-free dry wt m^?2. The annual production of the invertebrates was estimated from their mean annual biomass and their annual P/B ratio. Production of the primary consumers (herbivores and detritivores) was 21.4 g ash-free dry wt m^?2 y^?1 and of secondary consumers (carnivores) 1.1 g m^?2 y^?1. The amount of invertebrate production available to the trout population and the importance of the species as food for trout are discussed.     

Physical conditions of propagation media and their influence on the rooting of cuttings

Summary The formation and subsequent growth of roots by cuttings of poinsettia, hydrangea, rose and azalea in various propagation media, Jiffy-7, Jiffy-9 and Grodan under different conditions of aeration was investigated. The interrelationships of the effects of air content of the media, temperature and light intensity on the rooting of poinsettia cuttings was also studied.With low air contents (0 cm moisture tension) in the propagation media the formation and growth of roots was strongly inhibited. The rooting performance of rose appeared to be less affected by the poor aeration. Increasing air content improved rooting but best results were obtained at moisture tensions of 4 to 8 cm. Rooting seems to be better correlated with oxygen diffusion rate (ODR) than with air content.For poinsettia cuttings the optimum temperature for rooting was 24 to 28°C. At low temperatures rooting was delayed while at higher temperatures it was almost completely inhibited. Callus formation increased with temperature but decreased with increasing moisture tension. Conditions which induced large callus formation inhibited root formation.High light intensity during rooting reduced overall rooting performance and the inhibition was most pronounced in conjunction with high moisture tensions.Report No. 255.     

Function and structure of the carotid body

The carotid body is involved in both respiratory and cardiovascular control through complex neural pathways. Its most essential function is the reflex adjustment of respiration according to the arterial blood gas values. The location of the chemosensor within the organ is still unknown and is the subject of intensive research, there being presently several theories that seek to describe the interplay between glomus (chief) cells, nerve terminals and other elements within the organ.     

Improved demonstration of exocytotic profiles in glomus cells of rat carotid body after perfusion with glutaraldehyde fixative containing a high concentration of potassium

Extensive secretion by exocytosis was demonstrated in the glomus (type I) cells of the adult rat after perfusion of carotid bodies with a potassium-rich (high K) glutaraldehyde fixative. Similar secretory profiles were very rare with a glutaraldehyde fixative containing a low concentration of potassium (low K). The increase in the incidence of exocytotic profiles in glomus cells with the high K fixative was highly significant, whereas no statistical difference could be observed in the incidence of coated pits with the different fixatives. Exocytotic profiles were characterized by the following features: (1) they predominated in non-synaptic regions, but were occasionally observed near synapses between two glomus cells; they were not observed near synapses between glomus cells and nerve terminals; (2) extruded electron-dense material associated with coating of the cell membrane was frequent; (3) different stages of dissolution of the extruded granule material was evident. The possible role of exocytosis as a mode of secretion in the glomus cells and the characteristics of the new high K-glutaraldehyde fixative are discussed.     

Central innervation of the pineal organ of the Mongolian gerbil

Nerve fibers connecting the brain with the pineal gland of the Mongolian gerbil (central pinealopetal fibers) were investigated by means of light and electron microscopy. Several myelinated fibers penetrate from the brain into the deep pineal gland, extend further into the pineal stalk and continue to the superficial portion of the pineal gland. In the centripetal direction these fibers were traced to the stria medullaris and to the habenular nuclei, where they turned laterad and then occupied a position immediately ventral to the optic tract. As shown in electron micrographs, lesions of the habenular area led to degeneration of myelinated fibers and nerve boutons in the deep pineal gland, the pineal stalk and the superficial pineal gland. Only boutons containing clear transmitter vesicles (devoid of a dense core) were observed to degenerate after the habenular lesions. On the other hand, removal of the superior cervical ganglia resulted in degeneration of boutons containing small (40 to 60 nm in diameter) dense-core vesicles. Several of the nerve fibers that penetrate into the deep pineal directly from the brain (central fibers) exhibited a positive reaction for acetylcholinesterase (AChE). AChE-positive perikarya were located in the projections of the stria medullaris, the lateral portions of the deep pineal, the area of the posterior commissure, and the periventricular gray of the mesencephalon. Such perikarya were found neither in the pineal stalk nor in the superficial pineal gland. These results present anatomical evidence that the pineal organ of the Mongolian gerbil receives multiple nervous inputs mediated by peripheral autonomic (i.e., sympathetic) nerve fibers, on the one hand, and by central fibers, on the other.