Aminoguanidine prevented impairment of blood antioxidant system in insulin-dependent diabetic rats.

Non-enzymatic glycation is implicated in the development of various diseases such as Alzheimer's and diabetes mellitus. However, it is also observed during the physiologic process of aging. There is considerable interest in the contribution of oxidative stress to diabetes mellitus. An increase in the generation of reactive oxygen species can occur by non-enzymatic glycation and glucose autoxidation. Both of these processes lead to the formation of AGEs (Advanced glycation end-products) that contribute to the irreversible modification of enzymes, proteins, lipids and DNA. In this study, the effect of chronic hyperglycemia on the antioxidant system of diabetic rats was evaluated. The working hypothesis is that the loss of glucose homeostasis reduces the capacity to respond to oxidative damage. The enzymatic activities of CAT (catalase), GPx (gluthatione peroxidase), GR (gluthatione reductase) and GSH (reduced gluthatione) were increased in the blood of healthy rats subjected to endurance training, whereas, in diabetic rats the activities of CAT, GPx and GR were unaltered by similar training. SOD showed low activity in endurance-trained rats. The administration of aminoguanidine (an inhibitor of glycation reactions) in the drinking water increased the activities of CAT, GPx and GR, suggesting that glycation may be responsible for the partial inactivation of these enzymes. These results indicate that the association of hyperglycemia with strenuous physical exercise may induce cellular damage by impairing the antioxidant defense system.

Molecular characterization of hemoglobin alpha-D chains from Geochelone carbonaria and Geochelone denticulata land turtles.

In order to help elucidate the evolution of alpha-globins, the complete cDNA and amino acid sequences of Geochelone carbonaria and Geochelone denticulata land turtles alpha-D chains have been described. In G. carbonaria, the cDNA is 539 bp with ATG start codon located at position 46, TGA stop codon at position 469 and AATAAA polyadenylation signal at position 520. In G. denticulata, the cDNA is 536 bp with ATG start codon located at position 46, TGA stop codon at position 469 and AATAAA polyadenylation signal at position 517. Both cDNAs codify 141 amino acid residues, differing from each other in only four amino acid residues. When comparing with human Hb alpha-chain, alterations in important regions can be noted: alpha110 Ala-Gly, alpha114 Pro-Gly, alpha117 Phe-Tyr and alpha122 His-Gln. There is a high homology between the amino acids of these turtles when compared with chicken alpha-D chains, progressively decreasing when compared with human, crocodile, snake, frog and fish alpha-chains. Phylogenetic analysis of alpha-D chains shows that those of turtles are closer to those of birds than to snakes and lizards.

Polyphosphate binding sites in Liophis miliaris hemoglobin: evidence with reduced nicotinamide adenine dinucleotide phosphate

The water-snake Liophis miliaris presentes hemoglobin which binds organic polyphosphate through a simple single-site per tetramer (Mol. Wt. 64500) as judged by titration curves of reduced nicotinamide adenine dinucleotide phosphate either in the presence or absence of inositol hexaphosphate. The site seems to have the same structural nature of that found on other hemoglobins and is able to strongly bind most of the known protein effectors such as inositol hexaphosphate, adenosine triphosphate or 2,3-disphosphoglicerate. The high association constant at pØ7 of reduced nicotinamide for the deoxy hemoglobin of about K (D) = 7 x 10***6 M***-1 comparaed to human hemoglobin (K(D) = 7 x 10***5 M***-1), and to that of adenosine triphosphate (its natural erythrocytic polyphosphate) still higher of about K(D) = 10***11 M ***-1, shows clearly the very high affinity of this snake hemoglobin for such allosteric effector. The results besides corroborating the dimer-tetramer transition mechanism proposed to describe the oxygen transport by the hemoglobin of Liophis miliaris - may explain the difficulties to obtain the oxy dimeric conformation of the protein by usual hemolysis and stripped off procedures