No abstract

No abstract

Alkyl-dihydroxyacetonephosphate synthase (alkyl-DHAP synthase) is a peroxisomal enzyme that plays a key role in ether phospholipid biosynthesis. To determine the turnover of alkyl-DHAP synthase in several peroxisomal disorders, pulse-chase experiments were performed. In control fibroblasts, mature alkyl-DHAP synthase displayed a half-life of 23 +/- 12 h. In Zellweger syndrome and rhizomelic chondrodysplasia punctata fibroblast cell lines, in which alkyl-DHAP synthase cannot be imported into peroxisomes, the enzyme was mainly detected in its precursor form. This precursor form showed a much shorter half-life, 5 +/- 2 h. In contrast, when the precursor protein accumulated inside the peroxisome of a particular neonatal adrenoleukodystrophy cell line in which processing does not take place, a half-life of 18 +/- 8 h, resembling that of the mature protein in controls, was observed. In a cell line from a patient with a single deficiency in the activity of alkyl-DHAP synthase, the mature form was detected and its radioactivity decreased with a half-life of 16 +/- 7 h. Collectively, these results provide an explanation for the instability of alkyl-DHAP synthase outside its target organelle. Additionally, they indicate that both the precursor and mature form of alkyl-DHAP synthase exhibit considerable intraperoxisomal turnover.

Tire/road noise is one of the most urgent problems in traffic noise abatement. Therefore, to facilitate the design process of low noise tire/road systems, the development of appropriate computational tools, accounting for the most relevant effects of the noise generation and radiation, seems essential. However, until now no physically based and validated models exist that can be used to determine the sound radiation of rolling vehicle tires within the relevant frequency range and with reasonable accuracy. The numerical model presented here is based on a simulation process that may be split into several analysis steps: computation of the nonlinear stationary rolling process, analysis of the tire dynamics caused by the road roughness, and computation of the sound radiation. This contribution is concerned with the latter part of the analysis procedure. For the sound radiation analysis, the vibrations on the tire surface are extracted from a preceding structural analysis and used as boundary conditions in the acoustic model. The acoustic simulation process is based on the finite/infinite element approach, where an improved variant of the so-called Astley-Leis elements is used to model the sound radiation. The efficiency of the employed numerical methods is somewhat essential, because computational costs generally restrict the frequency range which can be simulated. By evaluating the sound pressure field, it is possible to compare the acoustic performance of specific tire/road systems, and the influence of certain parameters, such as the road texture or the impedance, on the noise radiation can be studied. The current work focuses on the validation of the computational model. Hence, characteristic results from the numerical simulations are compared with corresponding measurement data obtained from different test setups, including standing as well as rolling tires. This paper is dedicated to Em. O. Univ. Professor Dipl.-Ing. Dr. Techn. Dr. H. C. Franz Ziegler on the occasion of his 70th birthday.