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Summary  

The thermodynamic properties of the cardiac and skeletal a-actin isoforms were studied to characterize the molecular bases of the functional differences between them with the method of differential scanning calorimetry (DSC). The thermal properties of the actin filaments were described in the presence of calcium and magnesium ions as well. Based on the calculated free energy changes the α-cardiac actin filaments appeared to be more stable in its physiologically more relevant, magnesium saturated form. The magnesium saturated form of the α-cardiac actin filaments seemed to be more stable compared to the calcium saturated form of it. The enthalpy and entropy changes could differentiate between the α-cardiac and α-skeletal actin isoforms and between the calcium and magnesium saturated cardiac actin isoforms as well. Our results can demonstrate that the few differences between the amino acid sequences of the α-actin isoforms have an influence on the thermal properties and maybe on the function of these proteins as well.

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Abstract  

The effect of phalloidin on filaments polymerized from ADP-actin monomers of the heart muscle was investigated with differential scanning calorimetry. Heart muscle contains α-skeletal and α-cardiac actin isoforms. In the absence of phalloidin the melting temperature was 55°C for the α-cardiac actin isoform and 58°C for the α-skeletal one when the filaments were generated from ADP-actin monomers. After the binding of phalloidin the melting temperature was isoform independent (85.5°C). We concluded that phalloidin stabilized the actin filaments of α-skeletal and α-cardiac actin isoforms to the same extent when they were polymerized from ADP-actin monomers.

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Summary  

The effect of pH was characterised on the thermal stability of magnesium saturated skeletal and cardiac α-actin isoforms with differential scanning calorimetry (DSC) at pH 7.0 and 8.0. The calorimetric curves were further analysed to calculate the enthalpy and transition entropy changes. The activation energy was also determined to describe the energy consumption of the initiation of the thermal denaturation process. Although the difference in T mvalues is too small to interpret the difference between the a-actin isoforms, the values of the activation energy indicated that the α-skeletal actin is probably more stable compared to the α-cardiac actin. The difference in the activation energies indicated that lowering the pH can produce a more stable protein matrix in both cases of the isoforms. The larger range of the difference in the values of the activation energies suggested that the α-cardiac actin is probably more sensitive to the change of the pH compared to the α -skeletal actin.

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Cyclin C is a highly conserved protein that is involved in divergent cellular processes. The exact roles of its isoforms are presently not very well defined and it is possible that there is a functional divergence amongst them. We therefore sought to assess the expression pattern of cyclin C1 and C2 isoforms in various human tissues and in cell cycle by using real-time PCR experiments. Our findings strongly suggest that the C2 isoform may play a presently unexplored and important role in mammalian testis and probably this isoform is the one that is mainly implicated in cell cycle regulation.

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Polistes dominulus is known to be an allergenically important social wasp. Its venom has four major allergens (ziv. phospholipase A1, hyaluronidase, antigen 5 and a serine-protease). Amino acid sequences of its serine-protease and Antigen 5 have been published. In this paper, the partial amino acid sequence of its venom phospholipase native protein is reported. Also, we give an account to the complete nucleotide sequence of Polistes dominulus venom phospholipase A1 gene, its isoforms and their complete deduced amino acid sequences. Their similarity to the other phospholipases A1 of the family: Vespidae is discussed.

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expression of the highly sialylated isoform of the neural cell adhesion molecule in neurons and astrocytes of the adult rat spinal cord. Neuroscience 4 , 619-623. Dorsal rhizotomy induces transient expression of the highly

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phenotypic adaptation as atrophy or hypertrophy ( 8 ). Low-frequency stimulated muscles increase the combination of slower myosin heavy chain (MHC) isoforms ( 7 ). Unloaded soleus muscle fibers show slow-to-fast MHC transition in a time-dependent manner

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Acta Biologica Hungarica
Authors: Edit Hermesz, Anett P. Gazdag, Ali K. Said, J. Nemcsók, and Magdolna Ábrahám

, G. S., Nakanishi, T., Muto, N., Tanaka, K. (2000) Two metallothioneins in the fresh-water fish, crucian carp ( Carassius cuvieri ): cDNA cloning and assignment of their expression isoforms. Biol. Pharm. Bull. 23 , 145

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Physiology International
Authors: J Fodor, A Gomba-Tóth, T Oláh, E Zádor, Zs Cs Tóth, I Ioannis, B Molnár, I Kovács, and L Csernoch

a shift from slow oxidative to fast glycolytic fiber type in the rat diaphragm including the shift from slow sarcoplasmic–endoplasmic reticulum Ca 2+ ATPase (SERCA2a) to the fast-type isoform, SERCA1 ( 9 ). However, no fiber-type shift was reported

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Acta Biologica Hungarica
Authors: Diana Hazai, Katalin Halasy, D. Mornet, F. Hajós, and Veronika Jancsik

Lumeng, C. N., Hauser, M. (1999) Expression of the 71 kDa dystrophin isoform (Dp71) evaluated by gene targeting. Brain Res. 830 , 174-178. Expression of the 71 kDa dystrophin isoform

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