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Stereochlaena cameronii, a grass widely distributed in south central Africa, possesses tolerance towards heavy metals. Its tolerance and accumulation of zinc, lead, copper, iron, manganese and magnesium as well as sulphur have been studied and compared with similar phenomena in two other local metal-tolerant grasses, Gynodon dactylon and Trachypogon spicatus, as well as in some herbs and trees. The grasses accumulate high levels of copper in their roots in contrast with the herbaceous plants which accumulate the metal in their leaves. Distribution of other metals between roots and leaves is variable and is related to soil composition. Heavy-metal tolerance in Stereochlaena cameronii does not appear to be dependent directly on sulphur or nitrogen metabolism. In S. cameronii from zinc-rich soil, the zinc is largely in insoluble form in the roots, but in plants from other soils about half of this metal is in soluble form. [ABSTRACT FROM AUTHOR]

Beef liver 5-aminolevulinate dehydratase was purified 700-fold by salt fractionation, heat treatment, gel filtration and ion-exchange chromatography. The final product was homogeneous by electrophoretic, ultracentrifugal and immunological criteria and had a molecular weight, by the low-speed equilibrium method, of 260000. Treatment with sodium dodecylsutfate and 2-mercaptoethanol dissociated the enzyme into dimeric subunits which could be further dissociated into monomeric subunits by treatment with 7.3 M guanidine hydrochloride and dithioerythreitol. The molecular weight of the monomeric subunit and the results of amino acid analysis suggested the presence of 14 subunits per mole. Carboxymethylation and hydrolysis showed the presence of 56 cysteine residues per mole, approximately half of which were available for titration with p-ehloromereuribenzoate in the urea-denatured enzyme. The enzyme has a pH optimum of 6.3 and a Km of 0.46 mM in the crude state and 0.15 mM when pure. Thiol activation was required for catalytic activity and some evidence was obtained for a requirement for zinc as a co-factor. Heavy metals inhibited the enzyme in a complex manner. Zinc acted as a competitive inhibitor, lead acted as a non-competitive inhibitor, while cadmium acted in a unique manner, causing inhibition at low concentrations of subtrate and stimulation at high levels of substrate. [ABSTRACT FROM AUTHOR]

The cellular location of lead and potassium has been studied in the lichen Cladonia rangiformis, collected from a lead-rich site. Elution of ions by dilute acid or their replacement by other ions has demonstrated that lead is ionically bound, most probably within the cell wall. The same techniques have shown a proportion of the total potassium to be also bound ionically in the cell wall. In addition potassium is present as freely diffusible material retained within the permeability barriers of the intact cell and also firmly bound in an insoluble form. The reported tolerance of lichens to heavy metals is discussed in relation to the demonstrated location of lead. [ABSTRACT FROM AUTHOR]

The flowering plant Becium homblei is able to accumulate copper and other heavy metals to a relatively high level in its leaves. Approximately 17% of the total copper is concentrated in cell walls where it is bound as an organic complex. Copper in water extracts of leaf tissue is not in free ionic form but is complexed with amino acids or peptides. In vitro experiments indicate the strong complexing powers with copper of certain substances in leaf tissue. [ABSTRACT FROM AUTHOR]

Studies the metal concentrations of Hypnum cupressiforme, Hylocomium splendens and Sphagnum magellanicum from different parts of Scandinavia. Mean concentrations of Cd, Co, Cr, Cu, Ni, Pb and Zn in Hypnum cupressiforme from southern Sweden; Metal gradients in a transect across southern Sweden; Differences between southern and northern Scandinavia; Metal concentrations of Sphagnum magellanicum from bog sites.

Two different cross striation patterns can be seen under the electron microscope when fibrin fibrils are treated with heavy metal salts. The first shows two bands of different intensities per period (Type I), while the second has four bands per period (Type II). In this work, the factors involved in the formation of this particular cross striation pattern have been investigated. The origin of the Type I pattern is attributed to a reaction between uranyl acetate or phosphotungstic acid with the polar groups of fibrin (positive staining). Type II pattern arises from the embedding of excess heavy metal salts in the loosely structured portions of the fibrin fi bill (negative staining). The sites of accumulation of the polar groups are not the areas of greatest mass density of the molecule. [ABSTRACT FROM AUTHOR]