Inhibitory effect of polyelectrolytes on oligomeric enzymes

The effect of polyelectrolytes on the stability and catalytic characteristics of oligomeric enzymes--pig muscle lactate dehydrogenase (LDH) and bovine liver glutamate dehydrogenase (GDH)--was studied by fluorescent spectroscopic and steady state kinetic methods. It was shown that the binding of negatively charged polyelectrolytes--polystyrene sulfonate, polymethacrylate, and polyphosphate--destroys the tertiary and partially the secondary structure of LDH and GDH, resulting in their complete inactivation at pH < 7. The concentrations of polyelectrolytes needed for inhibition of the enzymes were in this case by two or more orders of magnitude lower than the corresponding concentrations for monomers--toluene sulfonate, methacrylate, and phosphate. The affinity of the substrate (pyruvate) for LDH did not vary in the presence of the polyelectrolytes, but the inhibition was removed by excess of substrate. We propose that the oligomeric state of enzymes causes polyelectrolytes to act on them in a special manner, this special effect differing significantly from the effect of polyelectrolytes on monomeric enzymes. The effect consists in that polyelectrolytes cleave the oligomeric structure of the enzymes, this "cleaving" effect being higher the greater the hydrophobicity of the polyelectrolyte chain.     

Left sided ablation for Atrioventricular Nodal Re-entrant Tachycardia: Frequency,Characteristics and Outcomes

BackgroundLeft-sided ablation, targeting left inferior AV nodal extensions, is thought to be necessary for success in a small proportion of atrioventricular nodal re-entrant tachycardia (AVNRT) ablations; however Indian data are scarce in this regard.MethodsConsecutive cases of AVNRT undergoing slow pathway ablation in a single centre over an 18-month period were retrospectively analyzed. Left-sided ablation at the posteroseptal mitral annulus was performed if right-sided ablation failed to abolish AVNRT.ResultsFrom January 2017 to June 2018, out of 215 consecutive supraventricular tachycardia (SVT) cases, 154 (71.6%) were AVNRT (47.1 ± 13.1 years, 46.1% male). Trans-septal ablation was required in 5 (3.2%) cases (mean age 48.8 ± 9.4 years; 4 female, 1 male); all with typical (slow-fast) form of AVNRT. Compared with cases needing only right-sided ablation, radiofrequency time (50.8 ± 16.9 vs. 9.9 ± 8.5 min; p = 0.005) and procedure time (166.0 ± 35.0 vs 79.6 ± 35.9 min; p = 0.004) were significantly longer for trans-septal cases, while baseline intervals and tachycardia cycle length were not significantly different. Junctional ectopy was seen in only 2 of the 5 cases during left-sided ablation, but acute success (non-inducibility) was obtained in 3 cases. There were no instances of AV block. Over mean follow-up of 12.2 ± 4.0 months, clinical recurrence of AVNRT occurred in one case, while others remained arrhythmia-free without medication.ConclusionLeft-sided ablation was required in a small proportion of AVNRT ablations. Trans-septal approach targeting the posteroseptal mitral annulus was safe and yielded good mid-term clinical success.     

Dyssynchronous Ventricular Activation in Asymptomatic Wolff-Parkinson-White Syndrome: A Risk Factor for Development of Dilated Cardiomyopathy

A subset of children and adults with Wolff-Parkinson-White (WPW) syndrome develop dilated cardiomyopathy (DCM). Although DCM may occur in symptomatic WPW patients with sustained tachyarrhythmias, emerging evidence suggests that significant left ventricular dysfunction may arise in WPW in the absence of incessant tachyarrhythmias. An invariable electrophysiological feature in this non-tachyarrhythmia type of DCM is the presence of a right-sided septal or paraseptal accessory pathway. It is thought that premature ventricular activation over these accessory pathways induces septal wall motion abnormalities and ventricular dyssynchrony. LV dyssynchrony induces cellular and structural ventricular remodelling, which may have detrimental effects on cardiac performance. This review summarizes recent evidence for development of DCM in asymptomatic patients with WPW, discusses its pathogenesis, clinical presentation, management and treatment. The prognosis of accessory pathway-induced DCM is excellent. LV dysfunction reverses following catheter ablation of the accessory pathway, suggesting an association between DCM and ventricular preexcitation. Accessory pathway-induced DCM should be suspected in all patients presenting with heart failure and overt ventricular preexcitation, in whom no cause for their DCM can be found.     

Functional Properties of Lactate Dehydrogenase from Dunaliella salina and Its Role in Glycerol Synthesis

The dependence of the catalytic properties of lactate dehydrogenase (LDH, EC 1.1.1.27) from a halophilic alga Dunaliella salina, a glycophilic alga Chlamydomonas reinhardtii, and from porcine muscle on glycerol concentration, medium pH, and temperature was investigated. Several chemical properties of the enzyme from D. salina differentiated it from the LDH preparation obtained from C. reinhardtii and any homologous enzymes of plant, animal, and bacterial origin. (1) V _max of pyruvate reduction manifested low sensitivity to the major intracellular osmolyte, glycerol. (2) The affinity of LDH for its coenzyme NADH dropped in the physiological pH region of 6–8. Above pH 8, NADH virtually did not bind to LDH, while the enzyme affinity for pyruvate did not change considerably. (3) The enzyme thermostability was extremely low: LDH was completely inactivated at room temperature within 30 min. The optimum temperature for pyruvate reduction (32°C) was considerably lower than with the enzyme preparations from C. reinhardtii (52°C) and porcine muscle (61°C). (4) NADH greatly stabilized LDH: the ratio of LDH inactivation constants in the absence of the coenzyme and after NADH addition at the optimum temperature in the preparation from D. salina exceeded the corresponding indices of LDH preparations from C. reinhardtii twelve times and from porcine muscle eight times. The authors believe that these LDH properties match the specific metabolism of D. salina which is set at rapid glycerol synthesis under hyperosmotic stress conditions. The increase of cytoplasmic pH value produced in D. salina by the hyperosmotic shock can switch off the terminal reaction of the glycolytic pathway and thus provide for the most efficient utilization of NADH in the cycle of glycerol synthesis. As LDH is destabilized in the absence of NADH, this reaction is also switched off. In the course of alga adaptation to the hyperosmotic shock, glycerol accumulation and the neutralization of intracellular pH stabilize LDH, thus creating the conditions for restoring the complete glycolytic cycle.     

Selection of active strains of Actinomadura carminata, the producer of carminomycin

The method of selecting active strains among a definite group of analogue-resistant mutants was used on the basis of studying the dependence of the carminomycin-producing organism growth and the antibiotic synthesis level on some metabolites. As a result, gamma-ray induced mutants 4 times more active than the parent strains were obtained.     

Dynamic aspect of kinetics of reaction catalyzed by lactate dehydrogenase

The influence of solvent viscosity on the kinetic parameters of the pyruvate reduction reaction catalyzed by lactate dehydrogenase has been investigated. The viscosity was adjusted by sucrose and glycerol solutions at concentrations from 0 to 44% and from 0 to 63%, respectively. The reaction rate decreased abruptly with an increase in viscosity. The study of different reaction stages (enzyme-substrate complex formation, catalysis, inhibitory complex decomposition, competitive inhibition by chlorine ions) revealed that the catalysis (and the related conformational changes) is the only stage (of the above mentioned) that depends markedly on the solvent viscosity. The reaction is insensitive to the changes in the dielectric properties of the solution induced by the addition of alcohols and dioxane. The observed power dependence of the rate constant on viscosity is explained in terms of Kramer's theory which considers the proton transition through the activation barrier to be a diffusion in the field of random forces. The influence of solvent viscosity on enzymic kinetics indicates a direct relation between solvent dynamics and relevant protein conformational movements.