Abstract Die Elektronenübergänge der Benzothiacyclene wurden experimentell durch Messung der Absorptions‐ und Polarisationsgradspektren bei 80°K und theoretisch durch quantenmechanische Näherungsrechnungen nach dem MIM‐ und PPP‐Verfahren untersucht. Die Beeinflussung von Intensität und Polarisationsrichtung der drei langwelligen μ*→μÜbergänge durch die unterschiedliche sterische Anordnung des Schwefelatoms wird von den Modellrechnungen richtig wiedergegeben. Es ergaben sich keine Hinweise auf die Beteiligung von 3 d ‐Orbitalen des Schwefels an der Konjugation mit dem Benzolring.
The rates of reaction of various exogenic iron(III) complexes with deuteroporphyrin IX in isolated mitochondria to form deuterohaem were measured. Ferritin was shown to supply iron readily for haem synthesis if the ferritin iron was reductively mobilised by the mitochondrial respiratory chain with succinate as substrate and FMN as mediator. In contrast, polynuclear complexes of iron(III) were able to form deuterohaem without added FMN. Rates of haem formation are about five times higher for the lowest polynuclear units than for ferritin. Sorbitol, gluconate, and bovine serum albumin were used as scavengers for polynuclear complexes with restricted size. Strong chelators of iron(II) compete favourably for deuterohaem formation, which supports the multistep mechanism for haem formation suggested by a priori arguments. Rates of deuterohaem formation were measured in homologous and heterologous systems of ferritins and mitochondria. Slightly differing rates of haem formation were shown to originate in different rates of iron mobilisation from the ferritins. The lack of species specifity in the interaction of ferritin with mitochondria also shows up in the linear dependence of ferritin binding on its bulk concentration as measured using 3H-labeled ferritin. Rates of haem formation are virtually the same in mitoplasts and mitochondria which indicates insignificant influences of the outer membrane. The hypothesis of low polynuclears as major components of the intracellular transit iron pool implies that both ferritin and transit iron pool species are largely equivalent sources of iron for mitochondrial haem synthesis.
A series of visual search experiments was carried out in order to verify the commonality of short-term search processes and selective attention. Experiment I used a multiple frame procedure and accuracy as a measure. It varied the relation of the target set to the distractor set, memory-set size, and frame size. To reach a given accuracy level, the presentation time per frame varied from 40 to 800 msec (or more) across conditions. The data showed evidence for slow serial search, termed controlled search, when the target and distractor sets varied from trial to trial, and fast efficient parallel search, termed automatic search, when the target and distractor sets were fixed from trial to trial. Experiment II used a single frame procedure and latency as a measure. Virtually all the accuracy effects of Experiment I were found in the latency results of Experiment II, and the two experiments were linked together. Experiment III was like Experiment I but presented more than one target per trial. The results qualitatively distinguished automatic from controlled search. First steps were taken toward a search model for selective attention.
