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Biomedical subjects

F Koenig

Publications and source records attributed to F Koenig.

At least 37 records · Page 2Linked to original sources
PubMed1983

[Hemorrhagic macular choroidopathy in the young subject].

In a group of 182 patients of under 50 years of age with subretinal neovascularization, the syndrome of hemorrhagic macular choroidopathy of the young adult was identified in 30 cases. This syndrome is characterized by the occurrence of a juxtafoveolar idiopathic neovascular membrane in an eye normal in all other respects. The natural course of this lesion is the production of a fibroglial scar leading to a mean final visual acuity of 0.15. The syndrome remains unilateral in 75 p. cent of cases, as shown by a mean follow-up of 23.9 months. Photocoagulation of these new vessels is possible, and in a group of 19 eyes it allowed conservation of a mean acuity of 0.6. This syndrome differs from ocular histoplasmosis where widespread uni- or bilateral involvement of the pigment epithelium and choriocapillaris is found. Hemorrhagic macular choroidopathy can also be distinguished from choroiditis associated with hemorrhages. The existence or the sequellae of uveitis, even when associated with subretinal new vessels arising from an atrophic chorioretinal scar, establishes the correct diagnosis. The etiology of hemorrhagic macular choroidopathy is unknown. It is possible that multiple etiologic agents might be responsible for different clinical syndromes in relation to endemic factors.

Adolescent↗
PubMedDate not supplied

Determination of the molecular weight and the hydrodynamic properties of a polypeptide from the thylakoid membrane by sedimentation, diffusion and binding measurements in dodecyl sulphate solutions.

The molecular weight and hydrodynamic properties of a polypeptide isolated from the lamellar system of Antirrhinum chloroplasts were determined in sodium dodecyl sulphate solution by measurement of sedimentation velocity, diffusion and effective partial specific volume. The polypeptide fraction exhibits a molecular weight of 25000 which agrees with the apparent molecular weight found by polyacrylamide gel electrophoresis. The molecular weight of the polypeptide-sodium dodecyl sulphate micelle was 54 000, with a friction ratio of 1.6 which indicates an effective asymmetric hydrodynamic shape. For binding measurements self-diffusion equilibrium dialysis with dodecyl [35S] sulphate was used. In this case, dialysis equilibrium was reached within about 10 hours, in contrast to the dialysis with initial concentration differences which requires much longer times. A binding value of deltaD=1.15 g sodium dodecyl sulphate per g polypeptide was obtained which corresponds to a molar binding ratio of 100 mol dodecyl sulphate bound per mol of polypeptide. After the removal of dodecyl sulphate the polypeptide is present in an aggregated state. In phosphate buffers of pH 6.8 and 7.5 the aggregates preponderantly have sedimentation coefficients of 11.7 and 6.8 Svedberg units respectively. Assuming equivalent spheres the molecular weights were calculated to be 340 000 and 150 000.

Chloroplasts↗
PubMedDate not supplied

Inhibition of electron transport on the oxygen-evolving side of photosystem II by an antiserum to a polypeptide isolated from the thylakoid membrane.

A polypeptide fraction with the apparent molecular weight 11 000 was isolated from stroma-freed chloroplasts from Anthirrhinum majus. An antiserum to this polypeptide fraction inhibits photosynthetic electron transport in chloroplasts from Nicotiana tabacum. The relative degree of inhibition is pH dependent and has its maximum at pH 7.4. The maximal inhibition observed was 93%. The dependence of the inhibition on the amount of antiserum yields a sigmoidal curve which hints at a cooperative effect. A calculation of the Hill interaction coefficient gave the value of 10. The inhibition occurs on the water splitting side of photosystem II between the sites of electron donation of tetramethyl benzidine and diphenylcarbazide. Tetramethyl benzidine donates its electrons before the site where diphenylcarbazide feeds in its electrons. Analysis of the steady state level of the variable fluorescence also indicates that the inhibition site is on the water splitting side of photosystem II. Tris-washed chloroplasts are equally inhibited by the antiserum and the inhibition is also observed in the presence of an inhibitor of photophosphorylation like dicyclohexyl carbodiimide and in the presence of the uncoupler carbonylcyanide m-chlorophenyl hydrazone (CCCP) which means that the inhibitory action is directed towards the electron transport chain. Valinomycin which is supposed to affect the cation permeability of the thylakoid membrane has no influence on the inhibitory action of the antiserum. The same is valid for gramicidin. Methylamine on the other hand can induce a state in the thylakoids in which the antiserum is not effective. If the antibodies are already adsorbed prior to the methylamine addition then the high inhibitory effect by the antiserum remains unchanged upon addition of methylamine. From the experiments it follows that a component from the vicinity of photosystem II is accessible to antibodies that is, the component is located in the outer surface of the thylakoid membrane. It appears that the inhibitory effect is produced in the course of the light reaction.

Benzidines↗
PubMedDate not supplied

Effect of an antiserum to a thylakoid membrane polypeptide on the primary photoreaction of photosystem II.

As was described previously, an antiserum to polypeptide 11000 inhibited photosynthetic electron transport on the oxygen evolving side of photosystem II. The effect of the antiserum on chloroplasts from two tobacco mutants also clearly showed that the inhibition site is on the photosystem II-side of the electron transport chain. One of the two tobacco mutants lacks the oxygen evolving capacity but exhibits some electron transport with tetramethyl benzidine, an artificial donor to PS II. In this mutant electron transport was barely inhibited. The effect of the antiserum on the primary photoevents showed that the initial amplitude of the absorption change of chlorophyll aII at 690 nm and that of the primary electron acceptor X320 at 334 nm both diminished in the presence of the antiserum. Both signals were restored upon addition of diphenylcarbazide another artificial donor to photosystem II. Comparison of the degree of inhibition on the amplitudes of the fast and slow components of the 690 nm absorption change with the manometrically measured inhibition of electron transport shows that besides a full inactivation of a part of the reaction centers of photosystem II another part apparently mediates a fast cyclic electron flow around photosystem II as reported by Renger and Wolff earlier for tris-treated chloroplasts. Moreover, the antiserum affects the low temperature fluorescence in a way which is opposite to Murata's effect of the Mg2+-ion induced inhibition of energy spill-over from photosystem II to phytosystem I. The antiserum under the condition in which the Hill reaction is inhibited lowered the 686 nm emission and enhanced the 732 nm emission which indicates an enhanced energy spill-over to photosystem I.

Chloroplasts↗