. Biological structure and function; proceedings. Biochemistry; Cytology. 90 LESTER PACKER with 1-25 X io~^ M ATP (curve B), The results show that the tension response is faster than ATP production by mitochondrial phosphorylation. Escape of ATP from the mitochondria may be the rate-limiting react'on, and this process may be connected with the extensive mitochondrial shrinkage states present. In summary, it was shown that changes in mitochondrial volume or membrane structure are brought about by changes in the activity of the respiratory chain. Certain evidence suggests that these structural c
. Biological structure and function; proceedings. Biochemistry; Cytology. 90 LESTER PACKER with 1-25 X io~^ M ATP (curve B), The results show that the tension response is faster than ATP production by mitochondrial phosphorylation. Escape of ATP from the mitochondria may be the rate-limiting react'on, and this process may be connected with the extensive mitochondrial shrinkage states present. In summary, it was shown that changes in mitochondrial volume or membrane structure are brought about by changes in the activity of the respiratory chain. Certain evidence suggests that these structural changes may lead to altered reaction rates of ATP-requiring systems which react at or near the membrane surface. The second point which I would like to consider is the locus of the coupling mechanism involved in the swelling-shrinking phenomenon, which has been raised by some experiments we have done with p-chloro- mercuribenzoate (PCMB). Certain striking similarities between this o 0-5. 200 400 600 800 Concentration of ADP or ATP (//M) Fig. 4. Contraction of glj'cerol-treated fibres of rabbit psoas muscle with ATP synthesized by rabbit cardiac muscle mitochondria (a) or ATP only (b). (Courtesy of the Journal of Biological Chemistry.) system and the contractile protein of muscle, myosin B, are apparent. Tapley [25] and Lehninger and Ray [26] have studied the action of PCMB on mitochondrial volume and report that it enhanced swelling. Significantly Lehninger and Ray [26] found that swelling was more rapid under aerobic than anaerobic conditions. Tapley [25] suggested that sulphydryl groups may be important in determining mitochondrial structure. In Fig. 5 the time course is shown of the effect of 83 /xM PCMB on shrinking and swelling of a suspension of cardiac mitochondria respiring different substrates. In the absence of substrate, PCMB exerts no appreciable effect upon mito- chondrial shrinkage for over 2 min., and then extensive swelling occurs. When, however, PCMB is added wh
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