GARY R. BURNS’s research while affiliated with Freie Universität Berlin and other places

Human erythrocyte ghosts were shown to have palmitoylating activity which acylates both endogenous ghost polypeptides and exogenous proteins derived from Semliki Forest virus (SFV). Cell-free fatty acid transfer from [3H]palmitoyl-CoA to endogenous protein was greatly enhanced in ghosts when pre-existing fatty acids linked to the endogenous acyl proteins were removed by hydroxylamine treatment prior to the transfer reaction. In contrast to erythrocyte acyl proteins acceptor proteins present in human placental membranes were palmitoylated in vitro to a similar extent with or without prior deacylation by hydroxylamine treatment. This indicates the presence of large pools of non-acylated proteins in placenta and small pools in erythrocytes. In testing for the protein substrate specificity of the palmitoyl transferase (PAT) present in ghosts we found that the SFV acceptor proteins, which are totally unrelated to erythrocytes, competed with the palmitoylation of endogenous ghost protein acceptors. This palmitoylating enzyme is inhibited by Cibacron Blue, SDS, and heat treatment, but stimulated in the presence of low concentrations of mild detergent (TX-100). Since PAT operating at the surface membrane of red blood cells has properties very similar to those of PAT present in human placental microsomes [1], we suggest that only one type of PAT may transfer fatty acids to various acylproteins that occur at multiple locations in different tissues [2].

Twelve years have passed since the initial report on the modification of viral proteins with covalently linked fatty acids appeared (Schmidt et al., 1979). With gratitude the first author and his students look back on a number of fruitful and happy years in Professor Rott's department, during which we contributed to furthering insight into the fatty acylation of proteins. Following the initial discovery this area has expanded tremendously, and as reflected by a great number of review articles (e.g. Schmidt 1982a; Low 1987, Schulz et al., 1988; Towler et al., 1988; Grand 1989; Schmidt 1989; Schmidt and Schlesinger, 1991) research on "hydrophobic modifications of proteins" has occupied virologists, cell-biologists and biochemists alike. Rather than duplicating the circulating reviews at this stage we take this occasion to report new data on the enzymatic nature of fatty acylation. We believe that the knowledge of the acylating enzymes will provide the cornerstone for full understanding of this hydrophobic modification of proteins.

XMM is a highly nested (58 individual shells) Wolter-I type X-ray telescope with a focal length of 7.5 m consisting of 3 individual modules. The specified resolution (HEW) is 30 (goal 15) arcsec. In order to qualify single mirror shells and align and assemble the whole mirror module in a reasonable time it is inevitable to apply fast test and strongly converging alignment procedures. By means of two scanning laser beams intra- and extrafocal images of two mirror shells will be registered on a CCD-camera coupled to an image processing PC. One of the mirrors is already glued and serves as a reference while the second one has to be aligned yet. From the data axial and lateral focus positions as well as focus dimensions are calculated. A feed back loop then shall activate a set of actuators coupled to the mirror to be aligned. In an iterative way the alignment status of this mirror will be optimized. Finally, this mirror is cemented under optical control. First results from a basic test setup with only one mirror will be presented. The work is performed under ESA contract for XMM.© (1989) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.