Pseudo-inhibitors of neutrophil superoxide production: evidence that soybean-derived polypeptides are superoxide dismutases

We have previously reported the purification of polypeptides from soybean which are potent inhibitors of superoxide production by human neutrophils. We now report that neither oxygen uptake nor hydrogen peroxide production by stimulated neutrophils is affected by these inhibitors. Furthermore, the E-1 and E-3 polypeptides inhibit ferricytochrome c reduction by a xanthine oxidase superoxide generation system. The inhibitory activity of E-3 in the model system is blocked by 1 mM KCN while E-1 is only slightly cyanide sensitive. Atomic absorption analysis of E-1 and E-3 polypeptides reveal copper in the latter and manganese in the former. Thus, E-3 is a copper-containing superoxide dismutase while E-1 appears to be a manganese-containing superoxide dismutase.     

Physicochemical characterization of large unilamellar phospholipid vesicles prepared by reverse-phase evaporation

Properties of large unilamellar vesicles (LUV), composed of phosphatidylcholine and prepared by reverse-phase evaporation and subsequent extrusion through Unipore polycarbonate membranes, have been investigated and compared with those of small unilamellar vesicles (SUV) and of multilamellar vesicles (MLV). The unilamellar nature of the LUV is shown by 1H-NMR using Pr3+ as a shift reagent. The gel to liquid-crystalline phase transition of LUV composed of dipalmitoylphosphatidylcholine (DPPC) monitored by differential scanning calorimetry, fluorescence polarization of diphenylhexatriene and 90 degrees light scattering, occurs at a slight lower temperature (40.8 degrees C) than that of MLV (42 degrees C) and is broadened by about 50%. The phase transition of SUV is shifted to considerably lower temperatures (mid-point, 38 degrees C) and extends over a wide temperature range. In LUV a well-defined pretransition is not observed. The permeability of LUV (DPPC) monitored by leakage of carboxyfluorescein, increases sharply at the phase transition temperature, and the extent of release is greater than that from MLV. Leakage from SUV occurs in a wide temperature range. Freeze-fracture electron microscopy of LUV (DPPC) reveals vesicles of 0.1-0.2 micron diameter with mostly smooth fracture faces. At temperatures below the phase transition, the larger vesicles in the population have angled faces, as do extruded MLV. A banded pattern, seen in MLV at temperatures between the pretransition and the main transition, is not observed in the smaller LUV, although the larger vesicles reveal a dimpled appearance.     

Involvement of histidine and tryptophan residues of glutamine binding protein in the interaction with membrane-bound components of the glutamine transport system of Escherichia coli

We treated the glutamine binding protein with diethyl pyrocarbonate (DEPC) and N-bromosuccinimide (NBS) to modify respectively the sole histidine and tryptophan residues and examined the effect of these modifications on the ability of the binding protein to bind glutamine as well as the ability to restore glutamine transport in membrane vesicles of Escherichia coli. Under the conditions used, both DEPC and NBS markedly inhibited the ability to restore glutamine transport in vesicles without any significant effect on glutamine binding. Moreover, saturating quantities of glutamine had no protective effect on the inactivation of the binding protein by DEPC or NBS. Fluorometric measurement and amino acid analysis indicate that the inactivation of the binding protein in restoring vesicle transport by NBS can be attributed to the oxidation of a single tryptophan residue. Similar analysis and the inability of hydroxylamine to reverse the effect of DEPC indicate that the effects of DEPC can probably be attributed to alterations of the sole histidine and/or one or more lysine residues of the binding protein. We conclude that the glutamine binding protein possesses at least two largely nonoverlapping functional domains, one responsible for glutamine binding and the other for the interaction with the other components of the glutamine transport system.     

Tubular Transport Maxima of PAH and Diodrast Measured Individually in the Aglomerular Kidney of Lophius, and Simultaneously as Competitors Under Conditions of Equimolar Loading

The maximal tubular transfer rates (Tm) of both p-aminohippurate (PAH) and diodrast (3,5-diiodo-4-pyridone-N-acetic acid or iodopyracet) were found to be fixed and reproducible when measured separately in Lophius (goosefish) under standard laboratory conditions. Expressed on a molar basis Tm_PAH was four times Tm_D. However, when these transport competitors were presented simultaneously in equimolar concentrations with the plasma levels of each sufficiently high enough to saturate the carrier system, the relative rates of excretion were reversed with the diodrast transfer rate then four times that of PAH. The combined rate of excretion was far below Tm_PAH alone, and roughly equal to Tm_D. Interaction with a common carrier was indicated by the gradations in degree of inhibition which resulted when plasma concentration ratios of diodrast to PAH were extended from 0.1 to 3.2, and PAH transfer rates expressed as percentage of Tm_PAH were correspondingly depressed from 17 to 1.0 per cent respectively. These observations again point up the inverse relationship between transfer rate and competitive effectiveness which exists for members of a series of substances actively transported by a common mechanism. It appears that carrier affinity and dissociation characteristics may be quite different for various compounds in a series, and also that these parameters may vary significantly from species to species.     

A Rapid Screening Test for Aflatoxin-synthesizing Aspergilli of the flavus-oryzae Group

A rapid test for the recognition of aflatoxin-synthesizing strains of the Aspergillus flavus–oryzae group is described. For this purpose the strains are cultivated on Czapek–Dox agar enriched with an aqueous extract of groundnuts, and in which sodium nitrate is replaced by ammonium chloride. Toxin production is observed by the production of a bright blue fluorescence in the medium when placed under an ultraviolet lamp.     

生态系统与耗散结构

1977年,比利时著名科学家伊·普里高津成功地提出耗散结构理论,荣获了诺贝尔奖。普里高津的理论告诉我们:“一个远离平衡态的复杂系统,各元素的作用具有非线性特点,正是这种非线性的相关机制,导致了大量离子的协同动作,突变而产生有序结构。”普里高津的耗散结构理论,研究系统怎样从混沌无序的动态向稳定有序的结构组织演化及其规律,故也称为非平衡系统自组织理论。这一系统理论的奇葩,对于生态系统的深入研究将起到不可估量的作用。同时,这一理论使我们对生态     

Molecular dissection of the NH2-terminal signal/anchor sequence of rat dipeptidyl peptidase IV

Dipeptidyl peptidase IV (DPPIV) is a membrane glycoprotein with a type II orientation in the plasma membrane. As shown in a cell-free translation system, the amino-terminal 34 amino acids of rat DPPIV are involved in translocating nascent polypeptide across the membrane of microsomes and in anchoring the translocated polypeptide in the microsomal membrane. The amino-terminal sequence performing this dual function is composed of: a central hydrophobic core of 22 amino acid residues; 6 amino-terminal residues preceding the hydrophobic core (MKTPWK); and 6 residues following the hydrophobic core. The six residues preceding the hydrophobic core are exposed on the outside (cytoplasmic side) of the microsomal membrane. Site-directed mutagenesis studies show that deletion of this cytoplasmic domain, excluding the amino-terminal initiating methionine, does not affect translocation of nascent DPPIV polypeptide, but does affect significantly anchoring of the translocated polypeptide in the microsomal membrane. In contrast, changing the two cytoplasmic Lys to Glu residues or shortening of the hydrophobic core from 22 to 15 residues or converting the last 11e of the shortened hydrophobic core into Ala affects neither translocation across nor anchoring of the DPPIV polypeptide in the microsomal membrane. These and other structural features of the DPPIV amino-terminal signal-anchor sequences are discussed along with other types of sequences for their role in targeting nascent polypeptides to the RER.