Differential effects of mercurial compounds on excitable tissues.

Sarcoplasmic reticulum (SR), Ca2+ plus Mg2+-ATPase, and Ca2+-ionophore were obtained from white rabbit skeletal muscles. Methylmercury inhibited the Ca2+ plus Mg2+-ATPase and Ca2+-transport but had no effect on the Ca2+-ionophore. Mercuric chloride inhibited all three functions (i.e., ATPase, transport and ionophoric activity). The mechanism of HgCl2 inhibition of the Ca2+-ionophore was by competition with Ca2+ for Ca2+-ionophoric site whereas its inhibition of the enzyme and Ca2+-transport was due to the blockage of essential sulfhydryl (--SH) groups. Ca2+ plus Mg2+-ATPase and Ca2+-transport were more sensitive to methylmercury than to HgCl2. Acetylcholine receptor (AChR) was obtained for the electric organ of T. californica. Methylmercury inhibited the ACh binding to AChR WITH Ki = 5.7 - 10(-6) M. This effect was not due to mercuric ion alone since mercuric chloride up to 10(-4) M did not affect ACh binding to AChR. It is concluded that: the Ca2+ plus Mg2+-ATPase and Ca2+-transport contain --SH groups essential for their activity, and that the two functions are tightly coupled; the Ca2+-ionophore contains no --SH groups essential for its activity; CH3HgCl inhibition of Ca2+ plus Mg2+-ATPase and Ca2+-transport is partly due to its reactivity with --SH groups in hydrophobic environment; the Ca2+-transport is inhibited by HgCl2 through two processes, one which is the blockage of --SH groups and another which is the inhibition of the Ca2+-ionophoric site; and the inhibition of ACh binding to AChR is due to the blockage of --SH groups in hydrophobic environment, which is inaccessible to Hg2+. Our data present for the first time a molecular basis for the myopathy associated with mercurial compounds toxicity.     

Purification and characterization of the 45,000-Dalton fragment from tryptic digestion of (Ca2+ + Mg2+)-adenosine triphosphatase of sarcoplasmic reticulum.

Tryptic digestion of (Ca2+ + Mg2+)-ATPase from sarcoplasmic reticulum of rabbit skeletal muscle has previously been shown to cleave the enzyme initially into a 55,000-dalton fragment and a 45,000-dalton fragment. In the present study the two fragments are solubilized in sodium dodecyl sulfate (SDS) and separated by preparative polyacrylamide gel electrophoresis. The 45,000-dalton fragment is found to be a relatively nonselective, divalent cation-dependent ionophore when incorporated into an oxidized cholesterol membrane (BLM). Ionophoric activity of this fragment is inhibited by low concentrations of LaCl3, HgCl2, and various reducing agents. There appears to be one or two relatively inaccessible disulfide bonds in the 45,000-dalton fragment that are essential for transport. Addition of reducing agents inhibits the ionophoric activity of the succinylated undigested enzyme and the 45,000-dalton fragment, but has no effect on the 55,000-dalton fragment. These experiments imply that the 45,000-dalton fragment and the 55,000-dalton fragment are in a series arrangement in the membrane.     

Angiotensin-(1-7) prevents diabetes-induced cardiovascular dysfunction

The aim of this study was to test the hypothesis that treatment with angiotensin-(1-7) [ANG-(1-7)] or ANG-(1-7) nonpeptide analog AVE-0991 can produce protection against diabetes-induced cardiovascular dysfunction. We examined the influence of chronic treatment (4 wk) with ANG-(1-7) (576 microg.kg(-1).day(-1) ip) or AVE-0991 (576 microg.kg(-1).day(-1) ip) on proteinuria, vascular responsiveness of isolated carotid and renal artery ring segments and mesenteric bed to vasoactive agonists, and cardiac recovery from ischemia-reperfusion in streptozotocin-treated rats (diabetes). Animals were killed 4 wk after induction of diabetes and/or treatment with ANG-(1-7) or AVE-0991. There was a significant increase in urine protein (231 +/- 2 mg/24 h) in diabetic animals compared with controls (88 +/- 6 mg/24 h). Treatment of diabetic animals with ANG-(1-7) or AVE-0991 resulted in a significant reduction in urine protein compared with vehicle-treated diabetic animals (183 +/- 16 and 149 +/- 15 mg/24 h, respectively). Treatment with ANG-(1-7) or AVE-0991 also prevented the diabetes-induced abnormal vascular responsiveness to norepinephrine, endothelin-1, angiotensin II, carbachol, and histamine in the perfused mesenteric bed and isolated carotid and renal arteries. In isolated perfused hearts, recovery of left ventricular function from 40 min of global ischemia was significantly better in ANG-(1-7)- or AVE-0991-treated animals. These results suggest that activation of ANG-(1-7)-mediated signal transduction could be an important therapeutic strategy to reduce cardiovascular events in diabetic patients.     

Incidence of Virulence Factors and Antibiotic Resistance among Enterococci Isolated from Food

The incidence of virulence factors among 48 Enterococcus faecium and 47 Enterococcus faecalis strains from foods and their antibiotic susceptibility were investigated. No strain was resistant to all antibiotics, and for some strains, multiple resistances were observed. Of E. faecium strains, 10.4% were positive for one or more virulence determinants, compared to 78.7% of E. faecalis strains. Strains exhibiting virulence traits were not necessarily positive for all traits; thus, the incidence of virulence factors may be considered to be strain specific.     

Mutation of E1-CONJUGATING ENZYME-RELATED1 decreases RELATED TO UBIQUITIN conjugation and alters auxin response and development

The ubiquitin-like protein RELATED TO UBIQUITIN (RUB) is conjugated to CULLIN (CUL) proteins to modulate the activity of Skp1-Cullin-F-box (SCF) ubiquitylation complexes. RUB conjugation to specific target proteins is necessary for the development of many organisms, including Arabidopsis (Arabidopsis thaliana). Here, we report the isolation and characterization of e1-conjugating enzyme-related1-1 (ecr1-1), an Arabidopsis mutant compromised in RUB conjugation. The ecr1-1 mutation causes a missense change located two amino acid residues from the catalytic site cysteine, which normally functions to form a thioester bond with activated RUB. A higher ratio of unmodified CUL1 relative to CUL1-RUB is present in ecr1-1 compared to wild type, suggesting that the mutation reduces ECR1 function. The ecr1-1 mutant is resistant to the auxin-like compound indole-3-propionic acid, produces fewer lateral roots than wild type, displays reduced adult height, and stabilizes a reporter fusion protein that is degraded in response to auxin, suggesting reduced auxin signaling in the mutant. In addition, ecr1-1 hypocotyls fail to elongate normally when seedlings are grown in darkness, a phenotype shared with certain other RUB conjugation mutants that is not general to auxin-response mutants. The suite of ecr1-1 molecular and morphological phenotypes reflects roles for RUB conjugation in many aspects of plant growth and development. Certain ecr1-1 elongation defects are restored by treatment with the ethylene-response inhibitor silver nitrate, suggesting that the short ecr1-1 root and hypocotyl result from aberrant ethylene accumulation. Further, silver nitrate supplementation in combination with various auxins and auxin-like compounds reveals that members of this growth regulator family may differentially rely on ethylene signaling to inhibit root growth.     

Cyclization of the Urokinase Receptor-Derived Ser-Arg-Ser-Arg-Tyr Peptide Generates a Potent Inhibitor of Trans-Endothelial Migration of Monocytes

The receptor for the urokinase-type plasminogen activator (uPAR) is a widely recognized master regulator of cell migration and uPAR_88-92 is the minimal sequence required to induce cell motility. We and others have previously documented that the uPAR_88-92 sequence, even in the form of synthetic linear peptide (SRSRY), interacts with the formyl peptide receptor type 1 (FPR1), henceforth inducing cell migration of several cell lines, including monocytes. FPR1 is mainly expressed by mammalian phagocytic leukocytes and plays a crucial role in chemotaxis. In this study, we present evidence that the cyclization of the SRSRY sequence generates a new potent and stable inhibitor of monocyte trafficking. In rat basophilic leukaemia RBL-2H3/ETFR cells expressing high levels of constitutively activated FPR1, the cyclic SRSRY peptide ([SRSRY]) blocks FPR1 mediated cell migration by interfering with both internalization and ligand-uptake of FPR1. Similarly to RBL-2H3/ETFR cells, [SRSRY] competes with fMLF for binding to FPR1 and prevents agonist-induced FPR1 internalization in human monocyte THP-1 cells. Unlike scramble [RSSYR], [SRSRY] inhibits fMLF-directed migration of monocytes in a dose-dependent manner, with IC₅₀ value of 0.01 nM. PMA-differentiated THP-1 cell exposure to fMLF gradient causes a marked cytoskeletal re-organization with the formation of F-actin rich pseudopodia that are prevented by the addition of [SRSRY]. Furthermore, [SRSRY] prevents migration of human primary monocytes and trans-endothelial migration of monocytes. Our findings indicate that [SRSRY] is a new FPR1 inhibitor which may suggest the development of new drugs for treating pathological conditions sustained by increased motility of monocytes, such as chronic inflammatory diseases.     

The effect of hydroxylamine on microsomal ATPase

The (Na⁺ + K⁺)-stimulated Mg²⁺-ATPase, but not the Mg²⁺-ATPase, is irreversibly inhibited when turtle bladder microsomes were incubated with hydroxylamine.

The Mg²⁺-dependent or the (Mg²⁺ + Na⁺)-dependent phosphorylation of ADP by the phospho-protein (the exchange reaction) is reversibly inhibited when the microsomes are incubated with hydroxylamine.

The Na⁺-induced increment of ³²P-labelling of microsomes previously incubated with [λ-³²P]ATP is completely eliminated by hydroxylamine, but the Mg²⁺-dependent ³²P-labelling of such microsomes is unaffected by hydroxylamine.

It is concluded that the phospho-enzyme formed during the Mg²⁺-dependent hydrolysis does not contribute to the Mg²⁺-dependent exchange reaction. Instead, the phosphoenzyme formed during the (Na⁺ + K⁺)-stimulated hydrolysis is apparently the only substance which phosphorylates ADP in the exchange reaction, even in the absence of Na⁺ and/or K⁺.

The hydroxylamine-sensitive nature of the sodium form of the phospho-enzyme in the (Na⁺ + K⁺)-stimulated ATPase sequence is consistent with the existence of an enzyme-acyl-phosphate bond of high internal energy with respect to that of ADP.

On the other hand, the hydroxylamine-resistant nature of the phospho-enzyme in the Mg²⁺-ATPase sequence suggests the existence of a non-acyl type of enzyme phosphate bond with low internal energy relative to that of ADP.