Adenosine diphosphate accumulation

To demonstrate polymerase activity in a model cell, Chakrabarti et al. [79] encapsulated polynucleotide phosphorylase in vesicles composed of dimyris-toylphosphatidylcholine (DMPC). This enzyme can produce RNA from nucleoside diphosphates such as adenosine diphosphate (ADP) and does not require a template, so it has proven useful for initial studies of encapsulated polymerase activity (Fig. 10a). Furthermore, DMPC liposomes are sufficiently permeable so that 5-10 ADP molecules per second enter each vesicle. Under these conditions, measurable amounts of RNA in the form of polyadenylic acid were synthesized and accumulated in the vesicles after several days incubation. The enzyme-catalyzed reaction could be carried out in the presence of a protease external to the membrane, demonstrating that the vesicle membrane protected the encapsulated enzyme from hydrolytic degradation. Similar behavior has been observed with monocarboxylic acid vesicles [80], and it follows that complex phospholipids are not required for an encapsulated polymerase system to function. 

Chlorophenols block adenosine triphosphate (ATP) production, without blocking the electron transport chain. They inhibit oxidative phosphorylation, which increases basal metabolic rate and increases body temperature. As body temperature rises, heat-dissipating mechanisms are overcome and metabolism is accelerated. Adenosine diphosphate (ADP) and other substrates accumulate, and stimulate the electron transport chain further. This process demands more oxygen in a futile effort to produce ATP. Oxygen demand quickly surpasses oxygen supply and energy reserves of the body become depleted. 

The covalent modification of proteins has been demonstrated to be an important and general in vivo mechanism for metabolic regulation (1). More recently it has been shown that nicotinamide adenine dinucleotide (NAD) can participate in such reactions as a donor of the adenosine diphosphate ribose (ADP-ribose) moiety (2, 3). Although the biological function of these reactions is still unknown, evidence has begun to accumulate suggesting that this class of modification constitutes an important regulatory mechanism. 

The sugar nucleotides (an uninformative name that has been used for glycosyl nucleotides, or more strictly, glycosyl esters of nucleoside di- or mono-phosphates) were discussed in this Series12 in 1973. Since then, accumulation of new data about these derivatives has continued, and now, about 35 representatives of this class are known to participate in the biosynthesis of polysaccharide chains of bacterial polymers (for a survey, see Ref. 13). These include glycosyl esters of uridine 5 -diphosphate (UDP), thymidine 5 -diphosphate (dTDP), guanosine 5 -diphosphate (GDP), cytidine 5 -diphosphate (CDP), cytidine 5 -monophosphate (CMP), and adenosine 5 -diphosphate (ADP). 

Development of differentiated cells of bacilli or strep-tomycetes is accompanied by accumulation of adenosine and guanosine highly phosphorylated nucleotides. Guano-sine-5 -diphosphate-3 -diphosphate (ppGpp) is known to act as a pleiotropic effector regulating metabolic pathways and transcription of different operons during nu-... 

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