Röntgenkleinwinkeluntersuchungen der strahleninduzierten Aggregation von Ribonuclease,Lactat-Dehydrogenase,Glycerinaldehyd-3-phosphat-Dehydrogenase und Serumalbumin. Ein Vergleich mit Malatsynthase

The X-ray induced aggregation of ribonuclease, lactate dehydrogenase (LDH), glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and serum albumin in aqueous solution was monitored in situ by means of small-angle X-ray scattering. The time dependence of several molecular parameters viz. the apparent radius of gyration \(\tilde R\) , the maximum visible diameterD, the mean degree of aggregation \(\bar x\) , and the mean radius of gyration \(\bar R\) was used to compare the various proteins with each other and with malate synthase which has been studied previously (P. Zipper andH. Durchschlag, Radiat. and Environm. Biophys., 1980). Measurements carried out with ribonuclease,LDH and serum albumin in the absence of dithiothreitol (DTT) and withGAPDH in the presence of 0.2mM DTT established the following series for the rates of aggregation of the proteins under these conditions: ribonuclease>LDH>GAPDH>serum albumin. The rate of aggregation ofGAPDH was found to be of similar magnitude as that obtained for malate synthase under comparable experimental conditions (presence of 0.2mM DTT, similar X-ray intensity) in our previous study. Within six hours from the beginning of irradiation (i.e. about the time required for the exposure of one complete scattering curve under the conditions of our experiments) the following increases of \(\tilde R\) resulted: ribonuclease 9%,LDH 7%,GAPDH 4%, serum albumin<1%. Changes of \(\tilde R\) exceeding 1% are, of course, too high to be tolerated in conventional scattering experiments.