Ribonucleotide reductase: A structural study of the dimeric iron site

The iron-containing B2 subunit of ribonucleotide reductase from Escherichia coli has been investigated by Raman spectroscopy. Both the tyrosyl radical-containing native protein and the radical-free protein exhibit a resonance-enhanced Raman band at 500 cm^?1. This band is assigned to an Fe-O vibrational mode arising from an oxygen-containing ligand. The failure to observe any tyrosinate ring modes makes it unlikely that ribonucleotide reductase is an iron-tyrosinate protein and rules out tyrosinate oxygen as a ligand. It is proposed that the 500 cm^?1 band in ribonucleotide reductase is analogous to the 510 cm^?1 Fe-O vibrational mode of methemerythrin and arises from an oxo- or carboxylate-bridge between the antiferromagnetically-coupled Fe(III) ions.     

Neue Vorstellungen zum Problem der Isoperoxidasen anhand der Trennung durch Disk-Elektrophorese und isoelektrische Fokussierung

Summary Isoelectric focusing (IEF) of peroxidases of different organs and tissues of Nicotiana tabacum L. was performed on thin-layers of Sephadex and polyacrylamide. Isoelectric points (pI's) of peroxidase bands were measured by special electrodes. — The two types of layers showed very similar results. Reproductibility of pI's was better on polyacrylamide. This method is also easier to practise and requires less time than IEF on Sephadex (3 h versus 18). Thus for analytical purposes the acrylamide-technique is preferable, but if it is necessary to regain the separated enzymes it is better to perform IEF on Sephadex. — When IEF-patterns of peroxidase are compared with the disk electrophoresis (DE) patterns of the same tissue, important differences are observed. The 6 bands of G_I (fast migrating, anodic group of DE) are reduced to 2 on the strongly acidic side of IEF (independent of the tissue studied). That means only 2 proteins in G_I can be separated by pI's of the molecules. Maybe the heterogeneity of G_I bands after DE indicates the presence of conformational isomers (conformers). — Because of the reduced number of bands in G_I after IEF there is no difference in the patterns of many tissues (flowers, leaves, shoots, pith) as there is after disk electrophoresis. In the case of G_II (slow migrating, anodic group of DE) on the other hand, there are always 4 different bands after isoelectric focusing in the lower acid region instead of 3 after disk electrophoresis. Disk electrophoresis of peroxidase-groups separated by isoelectric focusing shows the same patterns as direct disk electrophoresis of the extract. The methods produce no artifacts. —Comparison of these results with the peroxidase-patterns of tobacco found by other workers and by other techniques leads to the conclusion that there exist at least 4 isoenzymes of peroxidase corresponding to the 4 groups G_I, G_II, G_III, and G_IV.

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Abkürzungen IEF Isoelektrische Fokussierung - DE Disk-Elektrophorese - pI Isoelektrischer Punkt     

Fatty acids and long-chain bases of gangliosides of human gastrointestinal mucosa

The fatty acid and long-chain base composition of five major gangliosides from human stomach and small and large intestine mucosa were analyzed with gas chromatography. All the gangliosides greatly resembled each other in the fatty acid pattern. The main fatty acids were C_16:0, C_18:0 and C_24:0. No hydroxy fatty acids could be detected. In all the gangliosides 4-sphingenine was the predominant long-chain base (70–75%). About 15% of the long-chain bases had 20 carbon atoms in their chain. No trihydroxy long-chain bases could be detected.     

Evidence for mobility of immunoglobulin domains obtained by spin-label method.

It is found that EPR spectra of immunoglobulins and their subunits spin-labeled by iminoxyl radical 2,2,6,6-tetramethyl-4-amino (N-dichlorotriazine) at pH 7.5 are similar in form and reflect the capability of spin-label to be in two states. Formation of specific complexes of spin-labeled antibodies with antigens is accompanied by increased correlation time of labels as well as by increased fraction of the labels in a more immobilized state. It is shown that splitting spin-labeled light chains to halves results in the label losing its capacity of being in the more rigid microenvironment. EPR spectra are interpreted as due to the relative motion of domains.