The effects of divalent salts and 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) upon nicotinamide adenine dinucleotide phosphate (NADP) reduction and P700 in isolated chloroplasts are described and compared with the influence of DCMU on oxygen evolution and P700 in intact cells. Most experiments were carried out with a steady-state relaxation spectrometer. A kinetic mechanism for the estimatio...

The role of divalent cations in the mechanism of pyrophosphate-activated, template-directed oligoribonucleotide ligation has been investigated. The dependence of the reaction rate on Mg2+ concentration suggests a kinetic scheme in which a Mg2+ ion must bind before ligation can proceed. Mn2+, Ca2+, Sr2+, and Ba2+ can also catalyze the reaction. Although Pb2+ and Zn2+ do not catalyze the reac...

The individual effect of different major cations (Ca2+, Mg2+, Na+, K+, and H+) on the acute toxicity of zinc to the waterflea Daphnia magna was investigated. The 48-h median effective concentration (EC50) in the baseline test medium (i.e., a standard medium with very low ion concentrations) was about 6 microM (Zn2+). An increase of Ca2+ (from 0.25 mM to 3 mM), Mg2+ (from 0.25 mM to 2 mM), and N...

VILIP and NCS-1, neural-specific, 22-kDa Ca(2+)-binding proteins possessing four EF-hands, were expressed in Escherichia coli to study their divalent cation properties. Flow dialysis (Ca2+ binding) and equilibrium gel filtration (Mg2+ binding) revealed that both recombinant proteins possess only two active metal-binding sites, which can accommodate either Ca2+ or Mg2+. VILIP binds cations witho...

Tight junctions play a key selectivity role in the paracellular conductance of ions. Paracellin-1 is a member of the tight junction claudin protein family and mutations in the paracellin-1 gene cause a human hereditary disease, familial hypomagnesemia with hypercalciuria and nephrocalcinosis (FHHNC) with severe renal Mg2+ wasting. The mechanism of paracellin-1 function and its role in FHHNC are...

A partially purified D-xylose isomerase has been isolated from cells of Streptomyces albus NRRL 5778 and some of its properties have been determined. D-Glucose, D-xylose, D-ribose, L-arabinose, and L-rhamnose served as substrates for the enzyme with respective Km values of 86, 93, 350, 153, and 312 mM and Vmax values measuring 1.23, 2.9, 2.63, 0.153, and 0.048 mumol min per mg of protein. The h...

In this work we selected double-stranded DNA sequences capable of forming stable triplexes at 20 or 50 degrees C with corresponding 13mer purine oligonucleotides. This selection was obtained by a double aptamer approach where both the starting sequences of the oligonucleotides and the target DNA duplex were random. The results of selection were confirmed by a cold exchange method and the influe...

Five metallic cations (Fe3+, Cr3+, Cal+, Mg2+, Mn2+; concentration range, 1.85 X 10-4 to 37 X 10-4 M) were incorporated individually as chlorides into nutrient broth and agar media used for the recovery of phenol-treated Escherichia coli. The effects observed varied with the concentration and the ionic species. In nutrient agar, Fe3+ and Cr3+ were generally beneficial but were toxic at 37 X 10-...

The passive binding of cations to submitochondrial fragments prepared by sonic oscillation of bovine heart mitochondria has been examined. At least two different types of binding sites can be distinguished. The first site appears to be phospholipid in nature and binds the following cations in the sequence indicated: La3+ > Ca2+ > Mg2+ > K+ and Na+. Each of these cations inhibits the binding of ...

Inwardly rectifying K+ channels are distantly related to their voltage-gated counterparts and possess a structural motif of only two putative transmembrane segments in each subunit. They are formed by the assembly of an unknown number of subunits. We have examined the subunit stoichiometry of a strongly rectifying K+ channel, IRK1, by linking together the coding sequence of three or four subuni...