Electrical properties of hydrated collagen. II. Semiconductor properties

The dc conductivity of hydrated bovine Achilles' tendon collagen has been determined as a function of hydration over a limited temperature range. At ambient temperature the conductivity changes from 10^?15 (Ω cm)^?1 in the dry state to about 10^?8 (Ω cm)^?1 at ～24% water content by weight. For all temperatures the conductivity increases exponentially with hydration obeying σ(h) = A exp (βh), where h is a measure of the hydration, A is independent of temperature, and the parameter β ～ T^?1. It is shown that the data may be described by an impurity-type mechanism in which the effective activation energy for the process is dependent on temperature and hydration. Conduction is assumed to be electronic with the impurity (water) acting as a donor. In the solid state the effect of water on the conductivity is reversible indicating the absence of chemical alteration of the hydrated collagen.     

Electrical properties of hydrated collagen. I. Dielectric properties

The effect of water on the low-frequency (10²-10⁵ H_z) complex permittivitv of native, sold-state collagen has been investigated experimentally. Measurements at ambient temperature show that dry collagen exhibits essentially no frequency or temperature dependence. As water is absorbed, both dielectric constant and loss factor increase simultaneously and rise sharply upward at a hydration level which may be associated with the completion of the primary absorption layer as determined from independent water absorption studies. The behaviour is qualitatively identical to that observed for other proteins and related materials. Temperature-dependent measurements made under vacuum conditions in the range ?196°C to +100°C are characteristic of the dielectric properties of the water in the sample. Dehydration produced by successive temperature recycling to the maximum temperature effectively eliminates any temperature or frequency dependence. A maximum in the temperature-dependent curves is found at about +40°C and is explained as the superposition of two processes: (1) the transition of water molecules from bound to free states, and (2) the difffusion of water molecules out of the system. The dielectric constant of dry collagen, after desorption at ambient temperature, is about 4.5. Desorption at elevated temperatures reduced the room temperature value to about 2.3 and the liquid nitrogen temperature value to a number indistinguishable from the optical value of n² = 2.16.     

Biological properties of selenobiotin.

Selenobiotin is an excellent growth factor, as efficient as biotin in supporting the growth of biotin requiring microorganisms. It is incorporated in carboxylases leading to active “selenocarboxylases”. With E. Coli, the activity of the selenoacetyl CoA carboxylase is very similar to that of the normal enzyme.     

Thermotropic properties of phosphatidylethanols.

Phosphatidylethanol is formed when ethanol substitutes in the transphosphatidylation reaction catalyzed by phospholipase D. The structural and thermotropic properties of dipalmitoylphosphatidylethanol and dimyristoylphosphatidylethanol have been studied using differential scanning calorimetry, fluorescence spectroscopy, and 31P nuclear magnetic resonance. These lipids exist in a bilayer phase with no indication of nonbilayer phase formation, as shown by 31P nuclear magnetic resonance. It was found that the phase behavior of these phospholipids before and during the main chain melting transition is different in 50 mM Tris buffer compared to salt solutions. The phase transition behavior and the 6-propionyl-2-(dimethylamino)naphthalene (Prodan) fluorescence spectra for both lipids are consistent with the formation of the interdigitated gel phase under certain conditions. Both lipids become interdigitated in Tris-HCl, and ethanol enhances the formation of this phase. Comparative studies of the 6-propionyl-2-(dimethylamino)naphthalene spectra in dipalmitoylphosphatidylglycerol, dielaidoylphosphatidylethanolamine, and dipalmitoylphosphatidylcholine further elucidate the value and limitations of this probe as a diagnostic tool for lipid structure.     

Antimicrobial properties of diacetyl.

Diacetyl preparations from three commercial sources were found to be essentially similar when tested primarily against a set of 40 cultures, including 10 of lactic acid bacteria, 4 of yeasts, 12 of gram-positive non-lactic acid bacteria, and 14 of gram-negative bacteria. The compound was effective at pH less than or equal to 7.0 and progressively ineffective at pH greater than 7.0. The lactic acid bacteria were essentially unaffected by concentrations between 100 and 350 micrograms/ml over the pH range of 5.0 to 7.0. Of the 12 gram-positive non-lactic acid bacteria, 11 were inhibited by 300 micrograms/ml at pH less than or equal to 7.0. The three yeasts and the 13 gram-negative bacteria that grew at pH 5.5 were inhibited by 200 micrograms/ml. Diacetyl was ineffective against four clostridia under anaerobic conditions. It was lethal for gram-negative bacteria and generally inhibitory for gram-positive bacteria. Nongrowing cells were not affected. The effectiveness of diacetyl was considerably less in brain heart infusion broth, Trypticase soy agar, and cooked-meat medium than in nutrient broth or plate count agar. The antimicrobial activity was antagonized by glucose, acetate, and Tween 80 but not by gluconic acid. As an antimicrobial agent, diacetyl was clearly more effective against gram-negative bacteria, yeasts, and molds than against gram-positive bacteria.     

Leukocyte relaxation properties.

Study of the mechanical properties of leukocytes is useful to understand their passage through narrow capillaries and interaction with other cells. Leukocytes are known to be viscoelastic and their properties have been established by micropipette aspiration techniques. Here, the recovery of leukocytes to their normal spherical form is studied after prolonged deformation in a pipette which is large enough to permit complete entry of the leukocyte. The recovery history is characterized by the time history of the major diameter (d1) and minor diameter (d2). When the cell is removed from the pipette, it shows initially a small rapid recoil followed by a slower asymptotic recovery to the spherical shape. In the presence of cell activation and formation of pseudopods, the time history for recovery is prolonged compared with passive cell recovery. If a protopod pre-existed during the holding period, the recovery only begins when the protopod starts to retract.     

Hyaluronate binding properties of versican.

We have previously cloned a large chondroitin sulfate proteoglycan (versican) from human fibroblasts. The primary sequence shows that the N terminus contains sequence homology with known hyaluronate-binding molecule, suggesting that versican can bind hyaluronate. To test this hypothesis we have reconstructed a full-length versican cDNA and a versican cDNA fragment encoding the N terminus and have transfected Chinese hamster ovary cells and mouse 3T3 fibroblasts, respectively, with these constructs. The transfected Chinese hamster ovary cells make a proteoglycan shown to be versican by enzymatic and immunologic analysis. No corresponding proteoglycan was seen in the control cells. Using hyaluronate affinity chromatography, we show that recombinant versican specifically binds hyaluronate and does not bind to heparin or chondroitin sulfate. The transfected fibroblasts make a 78-kDa truncated form of versican that also binds hyaluronate and does not bind the related polysaccharides, showing that the hyaluronate binding activity resides at the N terminus of versican. The binding of versican to hyaluronate is substrate-concentration dependent and time dependent and can be competed with unlabeled versican. The dissociation constant for versican binding to hyaluronate was determined to be 4 x 10(-9) M.     

Purification and properties of staphylocoagulase.

Staphylocoagulase, an exoprotein of coagulase-positive Staphylococci, has been purified to a state in which only trace amounts of contaminating proteins are detectable. Aspartic acid was found as a single N-terminal amino acid in this preparation. The molecular weight is 61 000; the isoelectric point lies as pH 4.53. The amino acid composition was determined.