Function of Lactate Dehydrogenase in Cardiac and Skeletal Muscle of Phrynocephalus Lizard in Relation to High-Altitude Adaptation

Poikilothermic animals living in high-altitude environments can be greatly affected by the anaerobic metabolism and lactate recycling, which are catalyzed by an enzyme called lactate dehydrogenase(LDH). However, the function and possible regulatory mechanisms of their anaerobic glycolysis remained elusive. We compared the difference in LDH between a native high-altitude(4 353 m) lizard, Phrynocephalus erythrurus, and a closely related species, Phrynocephalus przewalskii that lives in intermediate altitude environment(1 400 m). The activity of LDH, the concentration of lactate, the distribution of isoenzyme, and the mRNA amounts of Ldh-A and Ldh-B were determined. In cardiac muscle, the lactate-forming activity of P. erythrurus in LDH was higher than of P. przewalskii LDH at all three temperatures tested(10 °C, 25 °C and 35 °C), while lactate-oxidation activity of LDH was significantly different between the two species only at 25 °C and 35 °C. In skeletal muscle, both lactate-forming and lactate-oxidation rates of P. erythrurus were lower than that of P. przewalskii. There was a higher proportion of H subunit and a significantly higher expression of Ldh-B, with a concomitant decrease of lactate concentration in P. erythrurus. These results indicate that P. erythrurus may have a strong potential for anaerobic metabolism, which is likely adapted to the hypoxic environment at high altitudes. Furthermore, P. erythrurus is capable of oxidizing more lactate than P. przewalskii. The Ldh-A cDNA of the two species consists of a 999 bp open reading frame(ORF), which encodes 332 amino acids, while Ldh-B cDNA consists of a 1 002 bp ORF encoding 333 amino acids. LDHA has the same amino acid sequence between the two species, but three amino acid substitutions(V12 I, N21S and N318K) were observed in LDHB. Structure analysis of LDH indicated that the substitutions of residues Val12 and Asp21 in P. erythrurus could be responsible for the highaltitude adaptation. The LDH characteristics of LDH in P. erythrurus suggest unique adaptation strategies of anaerobic metabolism in hypoxia and cold environments at high altitudes for poikilothermic animals.

Inactivation of Lactate Dehydrogenase from Pig Heart by o-Phthalaldehyde

Treatment of lactate dehydrogenase (LDH) with o phthalaldehyde resulted in a time dependent loss of enzyme activity. The inactivation followed pseudo first order kinetics over a wide range of the inhibitor. The second order rate constant for the inactivation of LDH was estimated to be 1.52 (mol/L) -1 ·s -1 . The modified enzyme showed a characteristic fluorescence emission spectrum with a maximum at 405 nm upon excitation at 337 nm, consistent with the formation of isoindole derivatives by the cross linking of proximal cysteine and lysine residues. The loss of enzyme activity was concomitant with the increase in absorbance at 337 nm. Stoichiometric study of the reaction showed that complete loss of activity was accompanied by formation of approximately four moles of isoindole derivatives per mole of LDH subunits. One of the substrates, NADH, partially prevented the enzyme from reacting with o phthalaldehyde, whereas the other substrate, pyruvate, did not provide any protection. Protection experiments suggest that one of the cysteine lysine pairs modified by o phthalaldehyde is near the NADH binding site of LDH.

Laboratory Indicators and Some Considerations in Albanian Patients with Beta Thalassemia Major and Sickle Cell Disease

Haemoglobinopathies are very serious clinical conditions caused by genetic mutations. They belong to autosomal recessive disorders and the most frequent genetic inherited diseases seen, specifically and above all among Mediterranean countries. Thalassaemia syndromes (included Beta Thalassaemia and Sickle Cell Disease) have been the first diagnosed diseases since in intrauterine life using reccombinant DNA techniques. So, the better understanding of their pathophysiology has given a spectacolar improvement and a considerable impact on these conditional managements. Every year there are nearly 300,000 children born with haemoglobinopathies globally, and there are 60,000 - 70,000 children with Beta Thalassemia among them. Nowadays in Albania like everywhere, there is a significant increase of survival in these patients. As a result of life longevity and improvement of patients life quality, we can see that these patients may suffer from other concomitant illnesses. In our country, there are registered approximately 500 patients with haemoglobinopathies. We studied 50 pediatric patients at random ranging from age 2 until 18 years old. We excluded other pathologies among them. We found high values of biochemical indicators in blood (Ca 15-3 was found elevated in 75% of our patients, Lactate Dehydrogenases was found elevated in 70% of cases, Indirect Bilirubin was found elevated in 66% of cases). All three parameters are indicators of hemolysis. We found a correlation between high values of Ca 15-3 marker and high levels of LDH, Indirect Bilirubin and low level of hemoglobin (p < 0.05). Ca 15-3 is much elevated among patients non regularly transfused and in those who take an unsufficient amount of blood. Continuous monitoring of these biochemical parameters is going to help in the more effective follow up of patients with haemoglobinopathies.