Sphaerapus,A Poorly Known Invertebrate Trace Fossil From Nonmarine Permian and Jurassic Strata of North America

In 1858, Edward Hitchcock named Sphaerapus larvalis and S. magnus for burrows from the nonmarine Lower Jurassic Turners Falls Formation in Massachusetts. Walpia hermitensis White, 1929, from the Lower Permian Hermit Shale, Arizona, is also a little known ichnotaxon. Examination of the type material indicates that Sphaerapus is a senior subjective synonym of Walpia. Sphaerapus is also a nomen oblitum, but Walpia has not been sufficiently used to replace its senior synonym as a conserved name; thus, we use the senior synonym Sphaerapus as the valid name of this ichnogenus, which is monospecific (S. larvalis = S. magnus = W. hermitensis). Numerous specimens of Sphaerapus from the Lower Permian of New Mexico and Texas, and a new record from the Lower Jurassic of Massachusetts show that it is a horizontal endichnion or exichnion having an unpacked tunnel with a cylindrical to ellipsoidal cross section, in some specimens branching, and lined with flattened, lenticular, non-coprolitic sediment pellets that are irregularly arranged and in some specimens imbricated. The pellets distinguish Sphaerapus from other endichnia. Sphaerapus resembles burrows of recent variegated mud-loving beetles and mole crickets, so Sphaerapus was likely produced by a hexapod similarly adapted for subsurface, compaction burrowing. Variation in pellet shape and arrangement in Sphaerapus reflects fluidity of the sediment burrowed, so this variation is a taphonomic artifact of no ichnotaxonomic significance. The latest Wolfcampian first appearance of Sphaerapus is not facies related, as similar facies lacking Sphaerapus are present in middle-late Wolfcampian strata. Therefore, the first appearance of Sphaerapus may reflect the evolutionary first appearance of a hexapod that moved through the sediment by compaction tunneling. However, the stratigraphically disjunct distribution of Sphaerapus may indicate that its preservation and fossilization were sensitive to paleoenvironmental and/or taphonomic factors that may also be involved in its first appearance.     

Linear aggregation and the turbidimetric lag phase: type I collagen fibrillogenesis in vitro.

Using classical light scattering theory it is shown that the turbidimetric lag phase is a property of macromolecular systems that form linear aggregates during the initial period of self-assembly. This analysis and previous observations on Type I collagen suggests that initiation occurs by the conversion of single molecules into linear dimers in which neighboring molecules are staggered by 4·0 D (D = 67 nm). Linear.growth of dimers occurs by 4 D addition of either single molecules or linear aggregates until the aggregate is about 60 to 70 molecules long. Linear growth appears to involve charged binding sites in the amino and carboxy termini. The same sites have been shown to be involved in crosslink formation and in the attachment of disaccharides.Lateral growth occurs via the rapid formation of several discretely sized intermediates which lead to the formation of narrow fibrils ～ 25 nm wide. Narrow fibrils individually wrap around each other increasing the diameter to 100 nm or greater.     

Mouse bone collagenase inhibitor: purification and partial characterization of the inhibitor from mouse calvaria cultures

The organ culture of neonatal mouse calvaria produced both collagenase and collagenase inhibitor. The inhibitor was purified by a series of column chromatographies: DEAE-cellulose and CM-cellulose ion-exchange chromatography, concanavalin A-Sepharose and heparin-Sepharose affinity chromatography, and finally by Sephacryl S-200 gel filtration. The purified inhibitor migrated as a single band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis and had a molecular mass of 28,000. The inhibitor was purified 140-fold to a specific activity of 163 units/mg with a yield of 18% over the first step of the purification by DEAE-cellulose chromatography. The inhibitor stained positively for carbohydrate with periodic acid-Schiff's reagent indicating, in conjunction with its affinity to concanavalin A, that the inhibitor is a glycoprotein. In addition to mouse bone collagenase, this inhibitor also inhibited chick bone, rat bone, rabbit corneal, and human gingival collagenase, but did not inhibit bacterial collagenase.     

The oxidation of endogenous ascorbic acid during histamine secretion by rat peritoneal mast cells

Endogenous ascorbic acid is oxidized to the free radical species by rat mast cells during histamine secretion. This antioxidant may function as a radical scavenger of Superoxide and other membrane-damaging radicals known to be liberated by this process. The high levels of ascorbic acid in mast cells may, therefore, function to protect the cell membrane from oxidative damage and thereby promote cell survival after an extensive secretory response.     

Demonstration of rotational symmetries in alpha-keratin microfibrils of porcupine quill tip

Selected electron micrographs of transversely, obliquely and longitudinally sectioned microfibrils of transversely sectioned porcupine quill tip are shown to possess 2-fold radial, 3-fold radial and 5-fold polygonal rotational symmetries. These symmetries are verified with a rotation technique, and are similar to edge, corner and face projections of a pentagonal dodecahedron. The a-keratin microfibril is therefore suggested to be composed of a linear arrangement of morphologically identical microfibrillar subunits which approximate the shape of a pentagonal dodecahedron. The various line patterns present in electron micrographs of microfibrils are explained by different orientations of this three-dimensional shape within the thickness of the section. Previous electron microscopic models for the structure of the microfibrils are incompatible with these results. The image averaging methods used to arrive at these earlier models are discussed, and are thought to yield results which must differ from the demonstrated rotational symmetries.     

Adhesion-guided multicellular assembly: a commentary upon the postulates, real and imagined, of the differential adhesion hypothesis, with special attention to computer simulations of cell sorting.

The condition for local dynamic stability of the trajectories of a metabolic network in the presence of conserved moieties and steady state subnetworks is given.     

The hierarchical structure of metabolic networks and the construction of efficient metabolic simulators

Methods are presented for the efficient simulation of large scale metabolic networks based upon the hierarchical structure of such networks and the formation of steady-state aggregations. The methods are dynamic and result in a varying time scale which is always consonant with the response of the network. An algorithm for the generation of reduced equivalent networks is presented. Problems of accuracy and stability are discussed. Special methods such as cascading and telescoping are presented for speeding the solution of the steady-state aggregations.