Wide occurrence of guanosine 5'-tetraphosphate in commercial preparations of GTP

New Insight into Plant Signaling: Extracellular ATP and Uncommon Nucleotides

New players in plant signaling are described in detail in this review: extracellular ATP (eATP) and uncommon nucleotides such as dinucleoside polyphosphates (NpnN's), adenosine 5'-phosphoramidate (NH2-pA), and extracellular NAD+ and NADP+ (eNAD(P)+). Recent molecular, physiological, and biochemical evidence implicating concurrently the signaling role of eATP, NpnN's, and NH2-pA in plant biology and the mechanistic events in which they are involved are discussed. Numerous studies have shown that they are often universal signaling messengers, which trigger a signaling cascade in similar reactions and processes among different kingdoms. We also present here, not described elsewhere, a working model of the NpnN' and NH2-pA signaling network in a plant cell where these nucleotides trigger induction of the phenylpropanoid and the isochorismic acid pathways yielding metabolites protecting the plant against various types of stresses. Through these signals, the plant responds to environmental stimuli by intensifying the production of various compounds, such as anthocyanins, lignin, stilbenes, and salicylic acid. Still, more research needs to be performed to identify signaling networks that involve uncommon nucleotides, followed by omic experiments to define network elements and processes that are controlled by these signals.

Presence of diguanosine tri, tetra-, and pentaphosphates in commercial samples of GTP and guanosine 5'-tetraphosphate

Commercial samples of GTP and guanosine 5'-tetraphosphate were analyzed, with or without previous treatment with alkaline phosphatase, by high-pressure liquid chromatography on a Hypersil ODS column. They showed the presence of diguanosine 5',5"'-Pl,Pn-tri, tetra-, and pentaphosphates in varying amounts depending on the sample, but usually in proportions of around 0.3%.

Presence of cytidine 5'-tetraphosphate in commerical samples of cytidine 5'-triphosphate

A contaminant compound has been isolated from commercial samples of CTP by ion-exchange chromatography on a Dowex-1 column. It has been characterized as cytidine 5'-tetraphosphate from its ultraviolet spectrum, labile and total phosphate content, and periodate consumption. It is present in proportions from 0.3 to 3.9%, apparently regardless of the method of preparation, age of sample, or commericial source of CTP.

Dinucleosidetetraphosphatase from Ehrlich ascites tumour cells: inhibition by adenosine, guanosine and uridine 5'-tetraphosphates

1. An enzyme has been partially purified from Ehrlich ascites tumour cells which specifically hydrolyses dinucleosidetetraphosphates, with Km values of around 2 microM. The products of the hydrolysis are the corresponding nucleoside tri- and monophosphates. Dinucleoside Tri- and diphosphates were not substrates of the reaction. 2. The enzyme requires Mg2+ or Mn2+, is maximally active at a pH value of approx. 7.5 and has a mol, wt of 19,800 as estimated by filtration on Sephadex G-75. Nucleoside mono-, di- and triphosphates were competitive inhibitors of the reaction with Ki values in the 0.1 mM range. 3. Particularly relevant is the inhibition of this enzyme by adenosine and guanosine 5'tetraphosphates. In the course of this investigation, the presence of uridine 5'-tetraphosphate was detected in a commercial preparation of UTP. Adenosine, guanosine and uridine 5'-tetraphosphates were very strong inhibitors of the reaction with Ki values in the nM range.