Spectroscopic effects of adenosine diphosphate upon the respiratory pigments of rat-heart-muscle sarcosomes

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Abstract
The results of Maley and Plaut (1953) on phosphorylative activities of rat-heart sarcosomes are confirmed and their P:O values are slightly exceeded: The average value of P:O ratio for [alpha]-oxoglutarate oxidation found here is 3.5. A high degree of respiratory control was demonstrated in these sarcosomal preparations and values for the ratio of more than 10 were often obtained. The relative amounts of the cytochrome components of the respiratory chain of the rat-heart sarcosomes are similar to those of rat-liver mitochondria, whereas the content of pyridine nucleotide relative to cytochrome is between 1/6 and 1/13 of that of the respiratory chain of liver mitochondria. Spectroscopic studies show that the initiation of oxidative phosphorylation by addition of adenosine diphosphate causes an oxidation of reduced pyridine nucleotide (absorbing at 340 m[mu]) and of cytochrome b. The latter result is not in agreement with that of Holton (1955) on cytochrome b, and 2 explanations for his results are considered. The cross-over point for the effect of addition of adenosine diphosphate upon the steady-state oxidation-reduction level of the cytochromes lies between b and c. This result is consistent with observations on mitochondrial preparations and indicates the similarity of the electron-transfer and phosphorylation mechanisms in heart sarcosomes andin liver mitochondria. The observations suggest that the response of the oxidation-reduction levels of the components of the respiratory chain to increases and decreases of concentration of adenosine diphosphate is a basic characteristic of the electron-transfer and phosphorylation mechanism and is to be found in sarcosomes and mitochondria of many cell types.