Since we hypothesized that the TC transition could have a direct impact on PARP enzyme activity through the V762A point mutation, we focused on analyzing data concerning genotype distributions from individuals who had been previously tested for PARP activity [15]. None of the genotype combinations at any locus studied showed any association with a high or low level of maximal PARP activity expressed in cpm/106 (by the Mann-Whitney test: locus TC; total n=95; TT(n=69) versus TC(n=19), P=0.89; TT(n=69) versus CC(n=7), P=0.89; TC(n=19) versus CC(n=7), P=0.88. Locus TC: total n=94 individuals; TT(n=39) versus TC(n=42), P=0.76; TT(n=39) versus CC(n=13), P=0.92; TC(n=42) versus CC(n=13), P=0.69). Moreover, no difference could be found between the values of specific PARP activity assembled according to the three possible combinations of genotype at these two loci (locus TC: total n=40 individuals; TT(n=27) versus TC(n=11), P=0.15; TT(n=27) versus CC(n=2), P=0.86; TC(n=11) versus CC(n=2), P=0.55. Locus TC: total n=38 individuals; TT(n=16) versus TC(n=18), P=0.81; TT(n=16) versus CC(n=4), P=0.63; TC(n=18) versus CC(n=4), P=0.86). In conclusion, the results of the analysis of PARP activity as a function of observed alleles at nucleotide positions 1011 and 244The text has already been shown to modify the thermo-sensitivity and finally the activity of a protein such as the methylenetetrahydrofolate reductase (MTHFR) [38]. Moreover, the C-terminus region, in which V762A is located, is the region most strictly conserved during evolution of the PARP-1 protein sequence. This segment can be separated from the rest of the protein, generating a 40 kDa C-terminal fragment that retains a basal level of catalytic activity [39]. The crystal structure of the catalytic fragment of chicken PARP-1 has been described [40]. Residue 762 is located in the helical domain of the catalytic fragment of PARP-1. As depicted in Fig. 5 (G. de Murcia, personal communication), the closest neighbor of residue 762 is G888. This amino acid is part of the PARP-1 signature (active site) and is totally conserved during evolution. Hence, in order to relate a specific genotype pattern to a high or low enzyme activity, we focused on genotype distributions from individuals who had previously been tested for PARP activity. However, none of the genotype combinations, at any locus studied, showed any association either with a particularly high or low maximal PARP activity (expressed in cpm/106) or with the specific enzyme activity. Finally, analysis of PARP activity as a function of the observed alleles at nucleotide positions 1011 and 2444 of PARP-1 cDNA did not reveal any significant difference between individuals with different genotypes. This suggests that the polymorphisms TC and TC at positions 1011 and 2444 do not have any impact on the activity of the enzyme. Likewise, in independent work, it was recently shown that putative differences in enzyme kinetic parameters of PARP-1, such as V and K, could not account for the maximum differences observed in the poly(ADP-ribosyl)ation capacity of human and rat cells [41], although the latter was positively correlated with the lifespan of these mammalian species [28]. However, one should keep in mind that in the present work, we have focused on seeking evidence for changes in the PARP-1 coding region that would confer increased specific activity in centenarians. Our findings might reflect the tip of the iceberg since (1) additional rare polymorphisms might exist in the coding region and (2) additional polymorphisms might exist in the non-coding region as well, for instance, in enhancer sequences far upstream of the coding sequences. Those may have an impact on the regulation of gene expression, and, hypothetically, changes in PARP-1 gene expression might influence the rate of PARP-1 protein turnover, and thus the functional status of PARP-1 protein. Using this reproducible and convenient method, we obtained data from 648 samples (324 centenarians and 324 controls). We calculated allele and genotype frequencies in each population to compare them and analyzed the association with human longevity. When we compared allelic frequencies and genotypes from the two populations studied, we found a clear absence of genetic association with human longevity both at the TC and the TC locus. We even observed a perfect identity of allele-frequencies between the two populations for the TC locus (Fig. 3). On the other hand, we expected that TC transition, which is responsible for a V762A exchange in the catalytic domain of the enzyme, would influence PARP activity. Although the structural consequence of a valine-to-alanine transition is expected to be rather weak, as it leads to the loss of a single methyl residue on the amino acid lateral chain, such an exchange has already been shown to modify the thermo-sensitivity and finally the activity of a protein such as the methylenetetrahydrofolate reductase (MTHFR) [38]. Moreover, the C-terminus region, in which V762A is located, is the region most strictly conserved during evolution of the PARP-1 protein sequence. This segment can be separated from the rest of the protein, generating a 40 kDa C-terminal fragment that retains a basal level of catalytic activity [39]. The crystal structure of the catalytic fragment of chicken PARP-1 has been described [40]. Residue 762 is located in the helical domain of the catalytic fragment of PARP-1. As depicted in Fig. 5 (G. de Murcia, personal communication), the closest neighbor of residue 762 is G888. This amino acid is part of the PARP-1 signature (active site) and is totally conserved during evolution. Hence, in order to relate a specific genotype pattern to a high or low enzyme activity, we focused on genotype distributions from individuals who had previously been tested for PARP activity. However, none ofConcept de base de Hayflick au concept de seuil critique d'accumulation d'erreurs. Pathol Biol: Harman D () Aging: a