The functional development of mammalian mitochondria

Human placental mitochondrial respiration and its regulation by adenine nucleotides

Respiratory parameters were studied in mitochondria from human placenta. Respiratory control and ADP/O ratios were low in this preparation. The adenine nucleotide content of placental mitochondria was found to be only one quarter of that found for adult uterine muscle tissue mitochondria prepared in the same way. Loading placental mitochondria with adenine nucleotides by incubation in the presence of ATP produced increased respiratory control ratios but no improvement in ADP/O ratios. Our evidence is consistent with the developmental changes shown to occur in rat liver, in which an increased concentration of adenine nucleotides is responsible for changes in respiratory parameters.

The use of antibiotics for studies of morphogenesis and differentiation in microorganisms

Numerous antibodies with a known mechanism of action are utilized as possible means for studying morphogenesis and differentiation. Inhibitors of biosynthesis of nucleic acids and proteins, compounds intervening with the synthesis and/or function of cell walls and membranes or compounds influencing the energy metabolism are particularly useful. The use of antibiotics for studies of the life cycle of viruses, bacteria, fungi, myxomycetes, protozoa and algae is analyzed in the present communication. Certain aspects of morphogenesis and functions of mitochondria and plastids were clarified with the aid of antibiotics. Relationships between production of antibiotics and differentiation of their producers are discussed in the final part of the paper.

Adrenocorticotropic hormone increases specific proteins of the mitochondrial fraction that are translated inside or outside this organelle in cultured adrenal tumor cells

In addition to its stimulatory effects on steroidogenesis, adrenocorticotropic hormone (ACTH) also has a trophic action on the adrenal cell. This is manifested in part by increases in the levels of key mitochondrial steroidogenic enzymes. The mechanism by which this trophic action of ACTH occurs has been studied in monolayer cultures of mouse adrenal cortical tumor cells. ACTH treatment of these cells stimulates the relative incorporation of amino acids into at least eight specific proteins in mitochondrial preparations. Two of these ACTH-responsive proteins are among the nine major adrenal polypeptides that fulfill the criteria of mitochondrial translation products: (i) their synthesis in intact cells is specifically resistant to inhibition by cycloheximide yet uniquely sensitive to chloramphenicol and (ii) they are synthesized in vitro by isolated mitochondria. The other six ACTH-responsive proteins are within the much larger category of mitochondrial proteins that are synthesized on cytoplasmic ribosomes. One of the proteins synthesized in the cytoplasm electrophoretically comigrates with purified beef adrenodoxin reductase and another with beef adrenodoxin. These findings indicate that ACTH regulates the synthesis (and turnover, or both) of specific mitochondrial proteins that are synthesized inside as well as outside the mitochondria of these adrenal cells.

Adequate function of the cell: interactions between the needs of the cell and the needs of the organism

The continuous maintenance of cell adequate function (cellular stress) is considered to be the main feature which characterizes the activity of a live cell. In accordance with the concept of cellular stress, the transition of the cell to the state of adequate functioning represents a dual commitment. The cell must function adequately to respond to the demands of the organism and to provide for its own needs. Thus, it is proposed that two systems exist for the regulation of the adequate function of the cell: one enabling the cell to respond to the demands of the organism, and the other providing for the needs of the cell itself. The hormonal system of the organism represents the first of these mechanisms, and I believe that another system exists for regulation of intracellular needs. Adequate function of the cell is determined by the regulative, controlling and defense mechanisms. The balance between the needs of the cell and of the organism should be a concern of physician, since it provides for the optimal function and health of the organism as a whole.

Toxic and mutagenic effects of carcinogens on the mitochondria of Saccharomyces cerevisiae

Nineteen haploid yeast (Saccharomyces cerevisiae) strains were used to assess the relative growth inhibitory potencies on fermentable vs. non-fermentable media of a collection of carcinogenic and non-carcinogenic chemicals. The majority of carcinogens were distinctly more potent on the non-fermentable (glycerol) medium, where mitochrondrial function is required for growth, than on the fermentable medium, where it is not. The anti-mitochondrial selectivity indicated by these growth tests was much slighter for the non-carcinogens. Similarly most carcinogens induced the cytoplasmic petite mutation whereas the non-carcinogens did not. Five carcinogens which were tested impaired the development of cytochromes aa3 and b in glucose cultures. Six carcinogens, when tested, inhibited growth on three fermentable sugars, the utilisation of which requires mitochondrial function. Out of five carcinogens which were examined, four suppressed the surface-dependent phenomenon of fluocculence in a flocculating strain of yeast, at concentrations primarily affecting the mitochondrial system; the fifth had a similar but less pronounced effect.