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Biomedical subjects

C Baumann

Publications and source records attributed to C Baumann.

At least 109 records · Page 6Linked to original sources
PubMed1973

Kinetics of rhodopsin bleaching in the isolated human retina.

1. Pieces of human retina were dissected from eyes enucleated because of malignant tumours. The isolated retinas were perfused by an ionic medium (36 degrees C) and investigated spectrophotometrically.2. Rhodopsin was identified on the basis of its difference spectrum. The maximum absorbance change on bleaching was about 0.1 (lambda = 500 nm).3. The process of bleaching was quantitatively analysed in terms of four slow reactions, viz. (a) conversion of metarhodopsin II into metarhodopsin III, (b) hydrolysis of metarhodopsin II into retinal and opsin, (c) decay of metarhodopsin III to retinal, and (d) reduction of retinal to retinol.4. First-order rate constants for the reactions in 3 were 9 x 10(-3) sec(-1) (a), 3 x 10(-3) sec(-1) (b), 4 x 10(-3) sec(-1) (c), and 3 x 10(-2) sec(-1) (d).5. With two simplified versions of the model summarized in 3 and 4, the description of experimental data was less accurate.

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PubMed1972

Kinetics of slow thermal reactions during the bleaching of rhodopsin in the perfused frog retina.

1. Slow thermal reactions occurring in the rhodopsin rods of flash-irradiated frog retinas were investigated spectrophotometrically.2. Five substances were identified as reactants: metarhodopsin II, metarhodopsin III, all-trans-retinal, opsin, and all-trans-retinol.3. Quantitative analysis showed that the transition between these substances are not a series of three consecutive reactions.4. An alternative scheme, compatible with the results, consisted of four reactions and involved two parallel pathways for the decay of metarhodopsin II, viz. conversion into metarhodopsin III, and hydrolysis into retinal and opsin.5. The first-order rate constants for the four reactions were as follows: 1.4 x 10(-2) sec(-1) for the conversion of metarhodopsin II into metarhodopsin III; 7.9 x 10(-3) sec(-1) for the hydrolysis of metarhodopsin II; 1.4 x 10(-3) sec(-1) for the hydrolysis of metarhodopsin III; and 2.6 x 10(-3) sec(-1) for the reduction of retinal into retinol (21 degrees C).6. Two other four-parameter schemes involving an equilibrium between metarhodopsin II and metarhodopsin III were also considered. One was found to be incompatible with the results. The other, though adequate, did not describe the data as well as the model summarized in 4 and 5. It also had the peculiar property of requiring that two apparently independent parameters be equated.

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