Poly nuclear enzymes

It is known that peroxynitrite is able to induce DNA strand breakage, which activates nuclear enzyme poly(ADP ribose) synthase (PARS). Szabo et al. [257] showed that the inhibition of PARS by oral treatment with lipophilic inhibitor 5-iodo-6-amino-l,2-benzopyr-one delayed the onset of arthritis in rats. It is possible that infrared pulse laser therapy can be useful for the treatment of RA patients [258]. 

The enzyme catalyzing the addition of ADP-ribose units onto the histones and itself is poly(ADP-ribose) polymerase or synthetase. Poly(ADP-ribose) polymerase is a nuclear, DNA-dependent enzyme that is stimulated by DNA breaks [302]. This property of the enzyme would target its action to sites that have DNA strand breaks (regions of the genome involved in replication, repair, recombination). The enzyme is associated with chromatin areas and perichromatin regions in interphase Chinese hamster ovary cells [312]. Degradation of the ADP-ribose polymer is catalyzed by the nuclear enzyme poly(ADP-ribose) glycohydrolase and ADP-ribosyl protein lyase. 

Addition of a poly-A tail Most eukaryotic mRNAs (with several notable exceptions, including those coding for the histones and some interferons) have a chain of 40 to 200 adenine nucleotides attached to the 3 -end (see Rgure 30.17). This poly-A tail is not transcribed from the DNA, but rather is added after transcription by the nuclear enzyme, polyadenylate polymerase. A consensus sequence, called the polyadenylation signal sequence (AAUAAA), found near the 3 -end of the RNA molecule, signals that a poly-A tail is to be added to the mRNA. These tails help stabilize the mRNAs and facilitate their exit from the nucleus. After the mRNA enters the cytosol, the poly-A tail is gradually shortened. 

Inactivation of DNA repair enzymes can also turn on apoptosis. A fascinating apoptotic process can result from stress or toxicity that culminates in genomic damage in the cell nucleus, triggered by a nuclear enzyme poly (ADP-ribose) polymerase... 

The poly(ADP-ribose) polymerase (PARP) hypothesis in which DNA strand breaks, induced by mustard, activates the nuclear enzyme PARP culminating in metabohc dismp-tion and protease activation in the region of the basal epidermal cells (Papirmeister et al., 1985). 

Poly(ADP-ribose) synthase (120, 142) is a eukaryotic nuclear enzyme that catalyzes three reactions the transfer of the ADP-ribose group of NAD + to other... 

In eukaryotic cells, DNA damage may induce a several thousand fold stimulation of poly(ADP-ribose) metabolism. A few restrictions and rules apply yeast does not express such a response, and in all other eukaryotes tested so far, the most effective types of DNA damages are those that are substrates for the DNA base excision repair pathway. By far the largest amount of ADP-ribose is processed throi the catalytic domains of two nuclear enzymes poly(ADP-ribose)polymerase-l, (PARP-1), and its catabolic counterpart, poly(ADP-ribose)glycohydrolase (PARC). Other members of the growing PARP family may contribute to this metabolism, albeit to a much lesser extent and with mechanisms that await further elucidation (for reviews see refs. 1,2). 

Lohinai Z, Mabley JG, Feher E et al. Role of the activation of the nuclear enzyme poly(ADP-ribose) polymerase in the pathogenesis of periodontitis. J Dent Res 2003 82 987-92. 

Bovine thymus poly(ADP-ribose) polymerase was purified to near homogeneity (95%) as described previously [11]. The enzyme reaction was carried out principally as described in a previous report [5], except that the buffer concentration of the reaction mixture was decreased to 5 roM. The reaction mixture contained 5 m/lf Tris-HCl buffer, pH 8.0, 1 vaM dithiothreitol, 10 roM MgQ, 10 Mg of calf thymus DNA, 2 mM NAD", 5 Mg of purified poly(ADP-ribose) polymerase, and an appropriate amount (1 to 15 Mg protein) of various nuclear enzymes in a total volume of 0.2 ml. The mixture was incubated at 25°C for 40 min and the reaction was terminated by chilling the sample on ice or by the addition of a final concentration of 50 mM nicotinamide. 

As summarized in Table 1, various nuclear enzymes involved in the function of chromatin were strongly inhibited when they were incubated in a reconstituted poly(ADP-ribose) S5mthesizing enzyme system purified poly(ADP-ribose) itself was slightly effective when it was added to the system in place of NAD, suggesting that poly-(ADP-ribos)ylation of the enzyme molecules caused the observed inhibition. Thus, the mechanism of the inhibition was studied for respective enzymes as described in the following sections. 

Table 1. Inhibition of various nuclear enzymes by poly(ADP-ribos)ylation in vitro ...

The present results demonstrated that several nuclear enzymes involved in function or metabolism of chromatin could be inhibitied by poly(ADP-ribos)ylation in vitro. Although a direct demonstration for the binding of poly(ADP-ribose) to some of the enzyme molecules has not been performed as yet, various indirect evidences strongly support the hypothesis that all of these enzymes are inhibited as a result of the modification of the enzyme molecules. 

K. Yoshihara et al. Poly(ADP-Ribos)ylation of Nuclear Enzymes... 

Sugimura T, Shimizu T (1968) Formation of poly(ADP-ribose) from NAD by nuclear enzyme preparations. Seikagaku 40 1-17... 

Our results demonstrate that by using cell fractionation procedures, it is possible to measure quite a significant level of poly(ADP-ribose) synthetase in the microsomal-ribosomal fraction of the testis and not in other somatic tissues. However, a major criticism to this experimental approach, is that the activity detected might well be due to a contamination with the nuclear enzyme. One fact that supports this criticism is that the nuclei contain a considerable amount of enzyme. On the other hand, no matter which procedure one uses to homogenize the tissue, the possibiUty of damaging the nucleus and consequently releasing some amount of enzyme, is difficult to discard. 

In the late 1970 s as evidence started to mount [1,2] linking poly(ADP-ribose) polymerase to DNA repair, this laboratory started to explore the possible clinical significance of this nuclear enzyme. A number of papers had already been published concerning the effects of carcinogens on the metabolism of nicotinamide, NAD, and poly(ADP-ribose). These results can be summarized as follows ... 

The enzymes of ADP-ribose metabolism have not yet acquired universally acceptable trivial names and the Enzyme Commission has not yet definitely decided on formal appellations. Consequently, a variety of names for the nuclear enzyme appear in this book, including nuclear(ADP-ribosyl)transferase, poly(ADP-ribose) polymerase, or synthetase or synthase. Hopefully, a common convention will soon be established. 

When brain or plasmacytoma mRNP particles were incubated with pancreatic RNAse or T1 RNAse the ADP-ribosyl transferase activity was increased at least by a factor or 2. Such an activation was not observed for nuclear ADP-ribosyl transferase or with a purified calf thymus nuclear enzyme supplemented with or without RNA. The chain length of poly(ADP-ribose) in mRNP proteins also increased after RNAse treatment from 3.9 to 4.7 in plasmacytoma (26-28). 

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