Respiratory and Enzymatic Properties of Squid Heart Mitochondria

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Abstract
Mitochondria isolated from systemic hearts of the squid I. illecebrosus showed high respiratory control ratios and, with appropriate substrates, the expected ADP/O ratios. Of amino acids tested, proline and ornithine were oxidized at highest rates; of carboxylates, malate, succinate and pyruvate gave the highest state-3 respiration rates. Pyruvate oxidation is enhanced with proline, ornithine and 1-pyrroline-5-carboxylate (pyrroline carboxylate) all of which can serve to augment the Krebs cycle. Proline, ornithine and pyrroline carboxylate oxidation is not similarly dependent upon pyruvate. Rotenone inhibited state-3 respiration of malate, proline, ornithine and pyrroline carboxylate. Neither intermediates of fatty acid oxidation nor glycerol 3-phosphate were utilized at significant rates. Key enzymes in proline and ornithine oxidation, i.e., proline dehydrogenase, pyrroline-carboxylate dehydrogenase, ornithine aminotransferase and glutamate dehydrogenase, were located in the mitochondria. The synthesis of proline is catalyzed by pyrroline-carboxylate reductase, which was found exclusively in the cytosol. The respiration, phosphorylation and enzyme data taken together suggest that the main C sources for heart mitochondria of Illex are pyruvate plus the proline and ornithine pool.