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Biomedical subjects

H A Lowenstam

Publications and source records attributed to H A Lowenstam.

12 recordsLinked to original sources
PubMed1992

Phosphatic shell plate of the barnacle Ibla (Cirripedia): a bone-like structure.

The carbonate apatite crystals and the segmented structure of the shell plates of the barnacles in the genus Ibla distinguish them from the shell plates of all other barnacles, which are coherent calcitic structures. A detailed study of the hierarchical organization of one of the two shell plate types, the tergum, reveals a remarkably complex structure. Cylinders composed of a chitin-protein complex and nodes of plate-shaped crystals constitute the basic building blocks. The crystals are organized into layered stacks in which the c crystallographic axes are all aligned perpendicular to a 25-nm banded structure. The cylinders are, in turn, ordered in arrays such that parts of each cylinder are aligned in a plane, and parts form arcuate out-of-plane structures. The overall result is a lamellar structure, with a plywood-like motif, that is present throughout an individual segment. A series of segments forms an interlocking mineralized core, which is enclosed within a thick organic envelope. The flexible and complex skeletal structure of the tergum shows some marked similarities to the structure of lamellar bone. Although this is undoubtably a product of convergent evolution, the iblid tergum provides a unique perspective on bone structure, which was heretofore unavailable.

Amino Acids↗
PubMed1981

Mössbauer spectroscopy of iron-containing dermal granules from Molpadia intermedia.

Dermal granules containing hydrous ferric oxide cores from Molpadia intermedia were studied by Mössbauer spectroscopy from 1.5 to 300 K and in magnetic fields up to 80 kOersted at 4.2 K. A magnetic phase transition to an antiferromagnetically ordered state is observed at 10 K. The results are compared with the magnetic behavior of micellar cores of ferritin from eukaryotes and iron-storage materials from prokaryotes.

Animals↗
PubMed1981

Minerals formed by organisms.

Organisms are capable of forming a diverse array of minerals, some of which cannot be formed inorganically in the biosphere. The initial precipitates may differ from the form in which they are finally stabilized, or during development of the organism one mineral may substitute for another. Biogenic minerals commonly have attributes which distinguish them from their inorganic counterparts. They fulfill important biological functions. They have been formed in ever-increasing amounts during the last 600 million years and have radically altered the character of the biosphere.

Animals↗
PubMed1980

Evolutionary prerequisites for early Phanerozoic calcareous skeletons.

This paper develops the concept that the dramatic appearance of calcareous skeletons in the Lower Cambrian is directly related to the origin of refined mechanisms of intracellular modulation of calcium ion concentration. An homologous family of calcium modulated proteins has recently been discovered. These proteins contain "EF hands", involved in the maintenance of low concentrations of intracellular calcium and the informational use of calcium ion flow (Kretsinger, 1977). The evolution of this specialized calcium physiology, especially in muscle systems, coupled with natural selection by predators are identified as some of the preadaptations for the impressive Tommotian diversification of calcified metazoans. The distribution of calcium biominerals in the phyla of the five kingdoms and the time of first appearance of calcareous mineralization in the fossil record are tabulated. Macroscopic calcified hard parts apparently required the prior evolution of certain cell, tissue and organ system physiologies which are briefly discussed here.

Animals↗
PubMed1976

Characterization of 80-million-year-old mollusk shell proteins.

Fossil glycoproteins of the soluble organic matrix are present in an 80-million-year-old mollusk shell from the Late Cretaceous Period. Discrete molecular weight components, as determined by gel electrophoresis, are preserved. The fossil organic matrix was compared with the organic matrix of a living representative species of the same superfamily. A particular repeating amino acid sequence, found in contemporary mollusk shell proteins, was identified in the fossil glycoproteins. The ultrastructure, mineralogy, and chemistry of the inorganic components of the fossil and contemporary shells provide information on the state of preservation of the fossil. The use of fossil shell proteins to further our understanding of molecular evolution is discussed.

Amino Acids↗
PubMed1975

Vaterite: a mineralization product of the hard tissues of a marine organism (Ascidiacea).

X-ray diffraction and infrared absorption spectra show that the spicules of the common tropical ascidian, Herdmania momus, are mineralized with vaterite. These are the first strictly marine organisms known to normally precipitate vaterite. The biomineralization of vaterite may constitute another link between the urochordates and vertebrates. The vaterite of ascidian spicules immersed in natural seawater remains mineralogically unchanged for 1 year, which indicates that vaterite may be preserved transiently in marine sediments.

Animals↗
PubMed1971

Opal precipitation by marine gastropods (Mollusca).

The high silicon content of certain radular sites of the Patellacea (Mollusca, Gastropoda) is shown by infrared absorption spectrums to be fixed in the form of the mineral opal. Opal and goethite mineralize the cusps and bases of the teeth. The presence of opalized base plates only in the families Acmaeidae and Lepetidae appears to be of taxonomic significance. Minimum values of the volume of fixation and of the turnover rate of opal by the Patellacea are calculated to assess the role of this previously neglected taxon in biological fixation of silica in the oceans. The significance of these organisms points to the much needed study of the silica transport system in tissue-grade Metazoa.

Animals↗
PubMed1968

Biologic precipitation of fluorite.

X-ray diffraction patterns show that the statoliths of marine mysid crustaceans are composed of fluorite, and that this mineral is also a principal phase of the gizzard plates of some tectibranch gastropods. A phosphatic phase is also indicated by chemical analyses in the gizzard plates, but its crystallochemical characterization has not been feasible by x-ray diffraction. The occurrence of fluorite in mysid statoliths confirms the earlier interpretations based on insufficient documentation. Fixation of fluorine in hard tissues of marine invertebrates is extensive in the shelf seawaters and minor in the bathyal zone of the oceans.

Animals↗
PubMed1967

Lepidocrocite, an apatite mineral, and magnetic in teeth of chitons (Polyplacophora).

X-ray diffraction patterns show that the mature denticles of three extant chiton species are composed of the mineral lepidocrocite and an apatite mineral, probably francolite, in addition to magnetite. Each of the three minerals forms a discrete microarchitectural unit of the chiton denticles. This is the first indication that lepidocrocite is precipitated by marine organisms and an apatite mineral by chitons.

Animals↗