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PubMed1980

The effect of alcohols on guanosine 5'-diphosphate-3'-diphosphate metabolism in stringent and relaxed Escherichia coli.

The effects of a series of alcohols on the stringent response system of Escherichia coli were studied. The alcohols used could be divided into two groups on the basis of the response of pppGpp and ppGpp to the growth downshift induced by the alcohols. The cells responded to the alcohols, methanol, ethanol, and propanol, as if they were being starved of amino acids. In the stringent strain CP78 these alcohols induced pppGpp and ppGpp accumulation and curtailed RNA synthesis, whereas in the relaxed strain CP79, both of these responses were absent. It was determined that this response was most likely due to an interference by these alcohols with the uptake of amino acids required by these strains. By contrast both stringent and relaxed cells elevated their level of ppGpp and decreased RNA accumulation when treated with butanol or pentanol. This response is similar to the effect of carbon source limitation. It was determined that the elevation of ppGpp in the stringent strain was primarily the result of increased ppGpp synthesis in response to these alcohols. In the relaxed strain the rise in ppGpp was dependent on a decrease in ppGpp degradation coupled with a moderate increase in ppGpp synthesis. This stimulation of ppGpp synthesis in relaxed cells, although small, suggests the existence of an enzyme distinct from stringent factor which is capable of synthesizing ppGpp. Data are presented which suggest that the activity of this enzyme is coupled to the potential for protein synthesis and energy availability of the cell, perhaps being regulated by the overall ratio of unchanged to amino-acylated tRNA.

Alcohols↗
PubMed1994

Purification and properties of geranylgeranyl-diphosphate synthase from bovine brain.

Geranylgeranyl-diphosphate synthase was purified to homogeneity from bovine brain in a one-step procedure employing an affinity column. For the construction of the affinity column, a farnesyl diphosphate analog, O-(6-amino-1-hexyl)-P-farnesylmethyl phosphonophosphate, was synthesized and linked to the spacer of the matrix of Affi-Gel 10 via the amino group. The native enzyme appeared to be a homooligomer (150-195 kDa) with a molecular mass of the monomer of 37.5 kDa. The pI for the enzyme was 6.2. The Km values for dimethylallyl diphosphate, geranyl diphosphate, and farnesyl diphosphate were estimated to be 33, 0.80, and 0.74 microM, respectively. The Km value for isopentenyl diphosphate in the reaction with isopentenyl diphosphate and farnesyl diphosphate was 2 microM. The reaction velocities for the formation of geranylgeranyl diphosphate from dimethylallyl diphosphate, geranyl diphosphate, and farnesyl diphosphate were in the ratio of 0.004:0.145:1. The intermediate farnesyl diphosphate was formed in the reaction with geranyl diphosphate as an allylic primer. Geranylgeranyl diphosphate acted as a competitive inhibitor against farnesyl diphosphate with an approximate Ki value of 1.2 microM in the condensation reaction of farnesyl diphosphate with isopentenyl diphosphate. Farnesyl-diphosphate synthase catalyzing the formation of farnesyl diphosphate from dimethylallyl diphosphate and isopentenyl diphosphate was also purified to homogeneity from the same organ by similar affinity chromatography using a geranyl diphosphate analog, O-(6-amino-1-hexyl)-P-geranylmethyl phosphonophosphate, as a ligand. This enzyme was a homodimer with a monomeric molecular mass of 40.0 kDa. These results indicate that geranylgeranyl diphosphate, a lipid precursor for the biosynthesis of a majority of prenylated proteins, is synthesized from dimethylallyl diphosphate and isopentenyl diphosphate by the action of farnesyl-diphosphate synthase catalyzing the reaction of C5-->C15, followed by the action of geranylgeranyl-diphosphate synthase catalyzing a single reaction of C15-->C20, and that geranylgeranyl diphosphate can down-regulate its own synthesis through the inhibition of the geranylgeranyldiphosphate synthase action.

Alkyl and Aryl Transferases↗