Francis O. Schmitt

Tropocollagen: significance of protease-induced alterations.

Interaction properties of tropocollagen are markedly altered by treatment with pepsin. This treatment liberates terminal or near-terminal covalently bonded peptides whose amino acid composition is strikingly different from the composition of the pepsin-resistant triple-helix body of the macromolecule. Pepsin also converts most of the β-chains to α-chains. This fact indicates that the interchain link is also external to the body of the macromolecule and probably involves peptides. The role of these properties in bioregulative mechanisms is briefly discussed.

The Structure of Certain Muscle Fibrils as Revealed by the Use of Electron Stains

Fibrils from certain molluscan muscles, in particular the adductor muscles of the clam Venus mercenaria, were examined with the electron microscope and found to possess periodic variations in structure. In order to make these structural variations visible, it was necessary to treat the fibrils with reagents of high electron scattering power (electron stains). Phosphotungstic acid was found to be particularly suitable. This stain combines with specific regions in the fibrils, forming a remarkably regular geometrical pattern of which the most prominent feature is a regular cross striation, representing a fiber‐axis spacing of about 145A. Within each stained band, the stain is more highly concentrated in spots spaced about 193A from center to center across the band. A line drawn through any such spot parallel to the fiber axis passes through other similar spots, spaced five cross bands apart, making the length of the fiber‐axis period precisely five times the fiber‐axis spacing. X‐ray diffraction data obtain...

X-ray Diffraction Studies on Nerve

FROM analysis by means of polarized light it has long been known that nerves possess a high degree of molecular organization. The axis cylinder is positively birefringent due to the presence of anisotropic material, the optic axis of which lies parallel to the long axis of the fiber. The myelin sheath is constructed of lipoid fluid crystals with optic axes perpendicular to the direction of the fiber and radially oriented (Schmidt, 18). The positive birefringence of the axis cylinder is due presumably to the protein neurofibrils which, though visible in fixed and stained preparations, have never been demonstrated in living medullated axons under physiological conditions (Peterfi, 16). In view of the success with which the x-ray diffraction method for fine-structure analysis has been applied to certain other fibrous animal tissues such as hair, chitin, connective tissue, etc., it is desirable that full use be made of this tool in the case of nerve, particularly since modern research on nerve energetics reve...

Some factors involved in the fibrogenesis of collagen in vitro.

Summary 1. A variety of organic substances derived from animal and plant sources can induce the precipitation of collagen- and long-spacing-type fibrils from acid extracts of ichthyocol in a manner similar to that of serum glycoprotein. These fibril-precipitating agents appear to be thermostable and are not altered by subsequent exposure to 20% trichloracetic acid. 2. Hyaluronate, chondroitin sulfate and heparin produce fibrous precipitates directly on addition to ichthyocol filtrates. At low ionic strength these fibrils are unstriated. At ionic strengths of 0.1 to 0.2 (NaCl) some long-spacing-type fibrils are formed but collagen-type fibrils have not been observed. 3. The components necessary for the formation of cross-striated fibrils appear to be contained in the fibrous material extracted from the connective tissue; the action of the precipitating substances seems to be relatively non-specific under the conditions of these experiments.

Structural Proteins of Cells and Tissues

Publisher Summary This chapter focuses on structural proteins of the cells and tissues. Proteins and complexes of proteins with lipids and carbohydrates form the basis of the structural components of cells and tissue. These structural proteins have, in the past, been investigated chiefly by the techniques of classical morphology, advances during the last two decades in the chemistry of these complex molecules and in physical techniques for investigating their internal architecture have laid the foundation for new correlations between structure and function. In this new synthesis, data of analytical chemistry must be related not only to ultrastructural considerations, but to the whole body of available information of morphology, physiology, and biochemistry. In certain tissues, such as muscle, it is possible to extract the structural protein and characterize its chemical and physical properties. The extraction of intracellular protein components by suitable reagents, such as water and salt solutions, and the isolation of these components by differential centrifugation has proven a powerful tool in determining the chemical composition and probable role of these constituents in the cell.

FIBROUS PROTEINS AND NEURONAL DYNAMICS

Publisher Summary This chapter presents, in historical perspective, the confluence of two major lines of investigation in neurobiology that, apart from helping to solve problems raised by each, adds new insight into the dynamic repertoire of the neuron. It discusses the general characterization of neuronal fibrous proteins. The chapter discusses the general characteristics of neuroplasmic rheology. Intracellular movement—whether of large organelles, such as chromosomes, cilia, flagella, sperm tails, or of particulates, such as pigment granules—occurs in many cell types and in conjunction with the microtubules of varying degrees of structural differentiation. Although the evidence remains circumstantial, the reasonable conclusion is that the two occurrences are causally related. The same situation exists in nerve axons; for example, the microtubules in sympathetic axons, observed with the electron microscope, are the only obvious structural mechanisms for the fast transport of catecholamine storage vesicles. Microtubules are responsible for at least a portion of neuroplasmic transport, most probably for which the velocities are high. The chapter also discusses chemomechanical transduction in neuroplasmic transport.

Molecular and ultrastructural correlates of function in neurons, neuronal nets, and the brain

I. Introduction The permanent storage of experiential information as psychological memory and its subsequent retrieval or recall, it is generally believed, is mediated by electric action-waves sweeping through complex branching sequences of neurons: neuronal nets. From what is currently known of neuroanatomy and of the dendritic and axonal branching, it would appear certain that these nets have numerous interconneetions. Therefore, if particular nets or subnets are to represent specific memory traces or engrams, it seems necessary to conclude that switching at net junctions must depend on subneuronal structures, possibly molecules or their aggregates. The process by which such switching might be permanently determined at the numerous junctions defining particular nets or engrams constitutes one of the most challenging problems of a field only now emerging: molecular neurology. The cellular and subcellular interactions by which genetic and immunological information can be stored, transferred, and read out or retrieved in macromolecular DNA, RNA, and protein polymers have been intensively investigated in recent years; this conceptually rich branch of the life sciences has come to be known as molecular biology or, more specifically, molecular genetics and molecular immunology. From the findings in these fields, some model of psychological memory might be sought. The phenomenology of immunology provides an example of plasticity, i.e., an adaptive modification of cellular and molecular specification in response to environmental changes, which may be analogous to the phenomena of permanent memory storage, where modification of structure may also occur in the formation of the permanent engram. Application of genetic and immunological concepts and techniques to the study of the engram as a macromolecular entity encounters difficulties of a temporal sort. Signaling in the nervous system is accomplished primarily by transient electrochemical changes in the surface membranes of neurons and synapses; the transduction of such signals into permanent molecular engrams probably requires incorporation of chemical groups into molecular structure with bonding stability of the order of that of covalent bonds. By what processes could ion fluxes or changes in the surface membrane or intracellular structures trigger and direct

Electron microscopy in morphology and molecular biology

Electron microscopy, in scarcely more than two decades, has led to revolutionary new concepts of cell structure and the mechanism of basic life processes. In many instances biological systems have been observed at or near the molecular level. These advances become the more significant because of profound parallel discoveries in biochemistry, biophysics, and biophysical chemistry in about the same period. The fusion of these sciences into a single unified effort has already been begun, leading toward what may appropriately be called molecular biology, a term early employed by one of the pioneers in the field, W. T. Astbury.

Fluid crystals and meristematic growth.

In an attack upon certain phases of the problem of meristematic growth, a cytological investigation of the cells of the squash root tip was made. Tissues fixed in fluids which preserve lipoidal structures, such as formalin-bichromate mixture, and osmic acid revealed structures which warrant description. The growing tips were fixed by two to three weeks impregnation in 2 per cent osmic acid, after the Kopsch-Mann technique. The sections were mounted in balsam unstained. In such preparations there appeared granules of varying sizes but of uniformly high refringency. These granules were practically round, and in ordinary light the centers appear lighter than the periphery. They are present in all parts of the tip. In the growing point they are small and occur from three to six to the cell and are usually clumped in one corner or are arranged along the cell wall. Some cells, however, appear to he devoid of these characteristic granules. In the highly vacuolated cells they are much larger and fewer to the cell than in the tip. In such cases they are almost invariably found to lie at the periphery of the vacuole, close to the cell wall. The object in making these osmic acid preparations was to determine whether any structures are present which might correspond to the Golgi bodies of animal cells. It is not certain whether these granules are actually Golgi bodies. Other granules which are not hirefringent are also present arid the probability is that they represent different stages in the metabolic activity of the cell. There is no evidence of a canalicular apparatus such as Bensley 1 found in the cells of the onion root tip. When these granules were studied with the polarizing microscope they were found to be uniaxial sphaero-crystals.

Macromolecular data processing in the central nervous system

Macromolecules and macromolecular aggregates physical and chemical properties importance to data processing activities in brain research