Gas stimulants

As discussed in Chapter 22, the activity of gnanyl cyclase is regulated by the messenger nitric oxide this gas stimulates the activity of this enzyme. Nitric oxide is generated from arginine catalysed by the enzyme nitric oxide synthase (NOS) (Figure 19.16). 

A close look at the events which occur during the lag period In GA Induction of novo synthesis of new enzymes has provided some Important clues as to whether GA acts at the transcriptional or translational level (16 and papers cited therein). An increase in polyribosome formation and an increased synthesis of ribosomes and endoplasmic reticulum membranes were found. All of these effects begin within 2 to 4 hr after application of GA. Their observations led Evins and Varner (16) to conclude that the GA-stimulated increases in the number of monoribosomes and the percentage of polyribosomes probably are prerequisite for the hormone induction of protein synthesis. 

Higgins at al. (17) provided a quite direct link between GA-stimulated dtt novo enzyme synthesis and appearance of the complementary mRNA. They demonstrated convincingly that the level of translatable a-amylase mRNA increased in GA-treated tissue in parallel with the increased rate of enzyme synthesis. These results provide still more evidence that GA acts to induce selective mRNA and de novo enzyme synthesis in aleurone cells. 

SAFETY PROFILE Moderately toxic by intravenous route. Experimental reproductive effects. Questionable carcinogen with experimental carcinogenic data. Mutation data reported. An experimental nerve gas stimulant. A flame retardant. When heated to decomposition it emits toxic fumes of POx. 

Tzou and Weller (1994) have studied the catalytic oxidation of dimethyl methylphosphonate (DMMP), a nerve gas stimulant, over laboratory-prepared Pt/AbOs as a function of Pt loading (0.5 or 2.0%) and temperature (150, 250, or 400 °C).A conventional flow system was used for the activity studies. They identified intermediate phosphorous-containing compounds in the reactor effluent after catalyst activity decline and looked for evidence of aluminum phosphate in the catalyst, which could be produced by reaction of alumina support with phosphoric acid. 

Toxicology LD50 (oral, rat) 8210 mg/kg, (IV, rat) 1050 mg/kg mod. toxic by IV route mutagenic data suspected carcinogen experimental reproductive effects experimental nerve gas stimulant TSCA listed... 

There is extensive evidence that GA increases auxin levels either by enhancement of auxin biosynthesis (Jindal and Hemberg 1976, Sastry and Muir 1965) or by retardation of auxin destruction (Kogl and Elema 1960). Nevertheless, there is convincing evidence that GA can also stimulate elongation independently of auxin (Kazama and Katsumi 1974, Cleland et al. 1968, Kaufman et al. 1969). In excised Avena stem internodes, for example, GA stimulates cell elongation, while auxin is inhibitory (Kaufman et al. 1969). Similarly, stimulation of lettuce hypocotyl elongation has been used as a bioassay for GA, while... 

GA stimulates ethylene production in first internodes of Phaseolus vulgaris (Abeles and Rubinstein 1964), but is ineffective in enhancing ethylene production in pea seedlings, at least during the first 6 days of growth (Fuchs and Liebermann 1968). 

Definitive proof for the de novo synthesis of a-amylase by GA-stimulated barley aleurone tissue was obtained by Filner and Varner [36] in 1967. They used a density-labelling technique which involved incubation of aleurone layers in (plus GA). The in the water becomes introduced as a density-label in the carboxyl oxygen of amino acids formed during breakdown of protein in the aleurone cells. 

Some workers have claimed that the number of ribosomes present in isolated barley aleurone cells increases in response to GA [35, 65] although others have shown no GA-stimulated synthesis of ribosomal RNA (or transfer RNA) [59, 109]. Since rRNA synthesis can be stopped in GA-treated aleurone layers without significant effect on either a-amylase synthesis or cellular rRNA levels [59] this can be taken as evidence that synthesis of new ribosomes is not... 

Induction of a-amylase synthesis Stimulated Pre-incubation of aleurone tissue with cytokinin enhances subsequent GA stimulation... 

Initially, about half a century ago, the apparently simple idea of collective atomic excitations, analogous to hydrodynamical oscillations of a homogeneous electron gas stimulated the development of extensive experimental and theoretical investigations. 

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