Inhibition of mushroom tyrosinase by 3-amino-L-tyrosine: molecular probing of the active site of the enzyme

We report the ability of 3-amino-L-tyrosine to act as a fully reversible competitive inhibitor of mushroom tyrosinase. The inhibition is linked to the ortho-aminophenol structure, and a copper bridging mechanism in the active site is proposed.     

Influence of the carbohydrate moiety on the growth inhibitory activity and adhesiveness of 3T3 cell plasma membranes

Summary Treatment of 3T3 cell plasma membranes with glycosidase enzymes decreased their ability to inhibit cell growth and also decreased their binding to 3T3 cells. This suggests that carbohydrate is required for complete function of inhibitory activity and that inhibition is associated with membrane adhesion.     

Inhibition of the growth of cariogenic bacteria in vitro by plant falvanones

Phytoalexins, defensive compounds produced by plants against microbial infections, were purified fromSophora exigua (Leguminosae) and their growth inhibitory effects on oral cariogenic bacteria were determined in vitro. Among three isolated compounds, 5,7,2,4-tetrahydroxy-8-lavandulylflavanone completely inhibited the growth of oral bacteria including primary cariogenic mutans streptococci, other oral streptococci, actinomycetes, and lactobacilli, at concentrations of 1.56 to 6.25 g/ml.     

Molecular ecology of a Neolithic meadow: The DNA of the grass remains from the archaeological site of the Tyrolean Iceman

The paper reports on the molecular analysis of samples of approximately 5,300-year-old grass found at the alpine archaeological site where the so-called Tyrolean Iceman was discovered. The grass comes from a cloak made of long grass blades and/or the stuffing of the snow footwear worn by the Iceman. The results show that while the largest fraction of the DNA extractable from the grass is of foreign origin, a much smaller part belongs to the original genetic material of the grass itself, and can be used as a valuable taxonomic clue to the plant species utilized by neolithic men to manufacture their equipment. On the other hand, the foreign DNA, or at least a portion of it, comes from microorganisms-mainly filamentous fungi and unicellular algae-which seem to have been associated with the grass since the time the grass was harvested.     

Inhibition by tetanus and botulinum A toxin of the release of [3H]noradrenaline and [3H]GABA from rat brain homogenate

Summary Rat brain homogenate was preloaded with [³H]noradrenaline or [³H]GABA and stimulated with high K⁺. Tetanus toxin and botulinum A neurotoxin partially prevent the evoked [³H]noradrenaline release in the same range of toxin concentrations starting below 10^–10M. In contrast, release of -amino butyric acid (GABA) is much more sensitive to tetanus than to botulinum A toxin.     

Family I.3 lipase: bacterial lipases secreted by the type I secretion system

Based on the classification of bacterial lipolytic enzymes, family I.3 lipase is a member of the large group of Gram-negative bacterial true lipases. This lipase family is distinguished from other families not only by the amino acid sequence, but also by the secretion mechanism. Lipases of family I.3 are secreted via the well-known type I secretion system. Like most of proteins secreted via this system, family I.3 lipases are composed of two domains with distinct yet related functions. Recent years have seen an increasing amount of research on this lipase family, in terms of isolation, secretion mechanism, as well as biochemical and biophysical studies. This review describes our current knowledge on the structure-function relationships of family I.3 lipase, with an emphasis on its secretion mechanism. Received 18 April 2006; received after revision 3 July 2006; accepted 24 August 2006     

Ecdysteroid conjugates in the ovaries of the silkworm,Bombyx mori: 3-phosphates of 2,22-dideoxy-20-hydroxyecdysone and of bombycosterol

Summary Two novel ecdysteroid conjugates, 2,22-dideoxy-20-hydroxyecdysone 3-phosphate (1) and bombycosterol 3-phosphate (2), as well as four known ecdysteroid 22-phosphate esters, have been isolated and characterized from the ovaries of the silkworm,Bombyx mori.     

The Arp2/3 complex: a central regulator of the actin cytoskeleton

In recent years the Arp2/3 complex has emerged as a central regulator of actin dynamics, assembling and cross-linking actin filaments to produce a diverse array of cellular structures. Here I discuss our current state of knowledge about this actin-remodelling machine. The predicted structure of the Arp2/3 complex can be directly correlated with its ability to nucleate, cap and cross-link actin filaments. A growing family of Arp2/3 complex activators such as the WASP family, type I myosins, and the newly identified activators cortactin and Abp1p tightly regulate this activity within the cell. Localised activation of the Arp2/3 complex produces structures such as lamellipodia or actin patches via a process termed dendritic nucleation. Furthermore, several pathogenic microorganisms have evolved strategies to 'hijack' the Arp2/3 complex to their own advantage. Finally, I discuss some of the questions which remain unanswered about this fascinating complex. Received 2 April 2001; received after revision 15 May 2001; accepted 18 May 2001     

Evidence of a direct action of triiodothyronine (T3) on the cell membrane of GH3 cells: an electrophysiological approach

Summary Electrophysiological experiments demonstrate that triiodothyronine (T₃) exerts a direct effect on the membrane of a strain of cultured rat pituitary tumor cells, GH₃/B₆. These cells respond to pressure application of T₃ (2–5 nl, concentration 1·10^–10 M) with an increase in the membrane resistance (R_m) and a hyperpolarization. Spontaneously firing cells become silent.     

Identification and biological significance of 4-methyl-3Z,5-hexadienoic acid produced by males of the gall-forming tephritidsUrophora cardui (L.) andUrophora stylata (Fab.) (Diptera: Tephritidae)

Summary A new natural substance has been identified in the rectal ampullae of gall-forming fruit flies. The substance was found to be the only volatile compound in the rectal ampulla of maleUrophora cardui andUrophora stylata. GC-MS methods were used to characterize its structure as 4-methyl-3Z,5-hexadienoic acid. Physiological parameters such as the amount of the acid at different ages and under different conditions were investigated. The biological significance of the new volatile as an arresting pheromone was tested in several bioassays. The arrestant function could not be established, but the results gave hints of a territorial function between conspecific males. The results are discussed with respect to gland morphology and predictions of communication models among fruit flies.     

Effect of platinum derivatives on the inducible and repressible liver microsomal enzyme systems in the rat: inhibition of zoxazolamine-hydroxylase and induction of dimethyl-nitrosamine demethylase isoenzymes by cis-dichlorodiamine platinum (cis-PtCl2(NH3)2) and ammonium hexachloroplatinum (PtC16(NH4)2)]

Two platinum derivatives, cis-PtCl2(NH3)2 and PtCl6(NH4)2 have been studied for their effects on the Rat on cytochrome P450 in hepatic parenchyma on zoxazolamine-hydroxylase, a typical inducible system and on the two isoenzymes of dimethyl-nitrosamine demethylase, typical repressible systems. The inhibitory effect of PtCl6(NH4)2 on zoxazolamine-hydroxylase activity, previously shown by the authors, has been confirmed. The cis-PtCl2(NH3)2 also significantly inhibits zoxazolamine-hydroxylase activity. On the other hand, both of the platinum derivatives decrease cytochrome P450 level and enhance the dimethyl-nitrosamine metabolism. These various effects and their relationship are discussed.