We have previously confirmed the original report of Fischer (1) that fibroblast cultures from several species, transformed to malignancy b y viruses or b y chemicals, generate high levels of fibrinolytic activity under conditions in which cultures of normal cells do not. We have since found t h a t a comparable fibrinolytic enzyme is produced by primary cultures of a large number of avian and mammalian tumors (2, 3) and by human tumor cell lines? The enzymatic basis for this tumor-associated fibrinolysis has been shown to depend on two proteins: one of these (the cell factor) is a protein produced by transformed cells, and the other (the serum factor) is a protein found in all vertebrate sera tested (2, 3). The serum factor has now been purified and rigorously identified as the known zymogen plasminogen;3 the cell factor is a specific serine protease that functions as a plasminogen activator3Because sera can be selectively freed of plasminogen by simple fractionation procedures and by affinity chromatography (4), ~' 4 the role of the fibrinolytic system as a determinant of established parameters of transformation can be assessed. We have therefore compared the effects of plasminogen-depleted serum with those of native and reconstituted serum on the following phenotypic properties that are considered to be associated with oncogenic transformation: (a) capacity to support growth of SV-40-transformed hamster embryo fibroblasts in soft agar; (b) capacity to mediate the de-

The growth conditions known to influence the occurrence of mitochondrial profiles and other cell membrane systems in anaerobic cells of S. cerevisiae have been examined, and the effect of the several growth media on the lipid composition of the organism has been determined. The anaerobic cell type containing neither detectable mitochondrial profiles nor the large cell vacuole may be obtained by the culture of the organism on growth-limiting levels of the lipids, ergosterol, and unsaturated fatty acids. Under these conditions, the organism has a high content of short-chain saturated fatty acids (10:0, 12:0), phosphatidyl choline, and squalene, compared with aerobically grown cells, and it is especially low in phosphatidyl ethanolamine and the glycerol phosphatides (phosphatidyl glycerol cardiolipin). The high levels of unsaturated fatty acids normally found in the phospholipids of the aerobic cells are largely replaced by the short-chain saturated acids, even though the phospholipid fraction contains virtually all of the small amounts of unsaturated fatty acid present in the anaerobic cells. Such anaerobic cells may contain as little as 0.12 mg of ergosterol per g dry weight of cells while the aerobic cells contain about 6 mg of ergosterol per g dry weight. Anaerobic cell types containing mitochondrial profiles can be obtained by the culture of the organism in the presence of excess quantities of ergosterol and unsaturated fatty acids. Such cells have increased levels of total phospholipid, ergosterol, and unsaturated fatty acids, although these compounds do not reach the levels found in aerobic cells. The level of ergosterol in anaerobic cells is markedly influenced by the nature of the carbohydrate in the medium; those cells grown on galactose media supplemented with ergosterol and unsaturated fatty acids have well defined mitochondrial profiles and an ergosterol content (2 mg per g dry weight of cells) three times that of equivalent glucose-grown cells which have poorly defined organelle profiles. Anaerobic cells which are low in ergosterol synthesize increased amounts of squalene.

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Growth under conditions of oxygen restriction results in a generalized decrease in the definition of the mitochondrial membranes, a decrease in the mitochondrial cytochromes, and a decrease in citric acid cycle enzymes of the obligate aerobic yeast Candida parapsilosis. Addition of unsaturated fatty acids and ergosterol to cultures exposed to limited oxygen results in improved definition of the mitochondrial membranes and an increase in the total mitochondrial cytochrome content of the cells. Euflavine completely inhibits mitochondrial protein synthesis in vitro. Its in vivo effect is to cause the formation of giant mitochondrial profiles with apparently intact outer membranes and modified internal membranes; the cristae (in-folds) appear only as apparently disorganized remnants while the remainder of the inner membrane seems intact. Cytochromes a, a3, b, and c1 are not synthesized by the cells in the presence of euflavine. Ethidium appears to have effects identical to those of euflavine, whereas chloramphenicol, lincomycin, and erythromycin have similar effects in principle but they are less marked. The effects of all the inhibitors are freely reversible after removal of the drugs. The results are discussed in terms of a functionally three-membrane model of the mitochondrion. In addition, the phylogenetic implications of the observed differences between this organism and the facultative anaerobic yeasts are considered.