a1_The purpose of the present study was to compare the ontogenetic development of the activity of myocardial energy-supplying enzymes in two mammalian species, differing significantly in their level of maturation at birth. The animals were investigated during the late prenatal period and 2, 7, 14, 21, 25, 30, 63, 120 and 730 days after birth in the rat and 2, 21, 84 and 175 days in the guinea-pig. The following enzymes were assayed in the right and left ventricular myocardium: lactate dehydrogenase (LDH, lactate uptake and/or formation), triose phosphate dehydrogenase (TPDH, carbohydrate metabolism), glycerol phosphate dehydrogenase (GPDH, glycerol-P shuttle)), hexokinase (HK, glucose phosphorylation), malate dehydrogenase (MDH, tricarboxylic cycle), citrate synthase (CS, tricarboxylic cycle) and hydroxyacyl-CoA dehydrogenase (HOADH, fatty acid breakdown). The rat heart, highly immature at birth, exhibits three different developmental patterns of energy-supplying enzymes, identical in both ventricles: (i) two mitochondrial enzymes of aerobic metabolism (CS, HOADH) and GPDH have a relatively low activity at the end of prenatal life; thereafter their activity steadily increases, approaching the adult levels between the 3rd and 4th postnatal weeks. A significant decrease was observed between the 4th and 24th months. (ii) MDH and LDH: prenatal values were significantly higher as compared with the 2nd postnatal day; after this period the activities increased up to adulthood (4 months) and decreased during senescence. (iii) The activities of HK and TPDH are characterized by only moderate changes during development. HK differs from all other enzymes by the highest prenatal values, which exceed even adult values. In contradiction to the rat heart, the developmental differences in more mature guinea-pig heart were significantly less pronounced., a2_The only ontogenetic differences observed were the lower activities of enzymes connected with aerobic metabolism at the end of the prenatal period. Our results point to possible differences in the development of adaptive metabolic pathways in animals with different levels of maturation at birth., A. Bass, M. Stejskalová, A. Stieglerová, B. Ošťádal, M. Šamánek., and Obsahuje bibliografii
The determination of cytochrome c oxidase (COX) activity represents an important indicator for the evaluation of cell oxidative capacity. However, it has been shown repeatedly that different factors modify the rate of COX activity under various experimental conditions. The most important concern the ionic concentrations of the medium and the application of various detergents for the solubilization of mitochondrial membranes. We found the highest activity of COX in rat heart homogenates and mitochondria at 40-60 mM potassium phosphate. The rate of COX activity is dependent on the detergent/protein (P) ratio. Using n-dodecyl-b-D-maltoside (lauryl maltoside, LM) as the detergent, we obtained the highest activity at LM/P ratios of (50:100):1. By kinetic measurements of low-affinity binding sites in heart mitochondria, we found Vlim values of 4.3 and 22.2 mmol cytochrome c per min per mg P in the presence or absence of lauryl maltoside, respectively. The Km values were 16.7 mmol in the presence or absence of lauryl maltoside. Our results thus indicate that 1) the exact assessment of COX activity in heart homogenates and mitochondria requires the determination of optimum phosphate concentrations in the medium used, and 2) even small modifications of the experimental procedure may induce significant differences in the maximum values of COX activity., A. Stieglerová, Z. Drahota, B. Ošťádal, J. Houštěk., and Obsahuje bibliografii