Kinetische Untersuchungen und Modellstudien zur Funktion essentieller Reste im aktiven Zentrum der L-Asparaginase II aus E. coli

Peroxisomes are compartments in cells called organelles that perform many different functions. In humans, peroxisomal defects result in serious disorders, leading to early death. Peroxisomes need proteins to perform their function but they cannot make these proteins themselves. Therefore, peroxisomes take up (import) proteins from the cytosol, which is the fluid that surrounds organelles inside cells. Under certain conditions, peroxisome numbers need to be increased in cells, and one way to achieve this is by the division of pre-existing ones. This process is termed ‘fission’ but we do not understand fully how this occurs. In this thesis, we have studied details of the peroxisomal fission and import processes by analysing them in yeast. Pex11p is a protein which is important for peroxisome fission. Pex11p reshapes the peroxisomal membrane so that peroxisomes can start dividing. We investigated how Pex11p is stimulated to perform this function and how it interacts with the peroxisomal membrane. Our studies indicate that membrane reshaping occurs due to Pex11p interacting with specific regions of the membrane. Proteins destined for peroxisomes contain Peroxisome Targeting Signals (PTS) that are recognized by proteins Pex5p and Pex7p. These receptors transport PTS containing proteins from the cytosol, where they are made, into peroxisomes. We have identified that Aspartate aminotransferase-2 (Aat2p) localises to peroxisomes despite lacking a classical PTS. Peroxisomal localisation persisted in the absence of Pex5p and Pex7p. Instead, Pex20p is required for targeting. Functional analysis suggests that Aat2p may contribute to the regulation of metabolism inside peroxisomes

Peroxisomes in intestinal and gallbladder epithelial cells of the stickleback, Gasterosteus aculeatus L. (Teleostei)

The occurrence of microbodies in the epithelial cells of the intestine and gallbladder of the stickleback, Gasterosteus aculeatus L., is described. In the intestine the organelles are predominantly located in the apical and perinuclear zone of the cells and may contain small crystalline cores. In gallbladder epithelial cells the microbodies are distributed randomly. The latter organdies are characterized by the presence of large crystalloids. Cytochemical and biochemical experiments show that catalase and D-amino acid oxidase are main matrix components of the microbodies in both the intestinal and gallbladder epithelia. These organelles therefore are considered peroxisomes. In addition, in intestinal mucosa but not in gallbladder epithelium a low activity of palmitoyl CoA oxidase was detected biochemically. Urate oxidase and L-α hydroxy acid oxidase activities could not be demonstrated.

Determination of nutrient salts by automatic methods both in seawater and brackish water: the phosphate blank

9 páginas, 2 tablas, 2 figurasThe main inconvenience in determining nutrients in seawater by automatic methods is simply solved: the preparation of a suitable blank which corrects the effect of the refractive index change on the recorded signal. Two procedures are proposed, one physical (a simple equation to estimate the effect) and the other chemical (removal of the dissolved phosphorus with ferric hydroxide).Support for this work came from CICYT (MAR88-0245 project) and Conselleria de Pesca de la Xunta de GaliciaPeer reviewe