Carbon source, cytochromes

In yeast, DPG synthesis has been genetically interrupted (Schlame, 2(XX)). The yeast grow without DPG at temperatures of between 16 and 30°C but fail to grow at 37°C on fermentable carbon sources such as glucose, a condition for which mitochondria are not required for ATP synthesis. These data support the idea that mitochondria perform a necessary function in yeast survival other than the generation of energy. The fatty acyl chain content of phospholipids can impact mitochondrial function. Incubation of car-diomyocytes with palmitic acid increased the palmitic acid content of PA and PG and decreased DPG levels in mitochondria with a concomitant release of cytochrome c leading to apoptosis (W. Dowhan, 2001). 

A newly isolated soil bacterium grows without oxygen but requires ferric ion in the growth medium. Succinate suffices as a carbon source, but neither hexoses nor pyruvate can be utilized. The bacteria require riboflavin as a growth supplement. Neither niacin nor thiamin is required, and neither substance nor compounds derived from them can be found in the cells. The electron carriers found in the bacteria are cytochrome b, cytochrome c, FAD, and coenzyme Q. 

Figure 2. The effect of the novel inhibitor of ubiquinone cytochrome c oxidoreductase on the growth ofthe wild-type ( ) andG143A( ) strains of S. cerevisiae using lactic acid as the carbon-source.

Polytox uses a consortium of bacteria from sewage sludge. Toxic chemicals inhibit the oxidation of a carbon source (presumably glucose). Presumably the toxic chemicals damage the cellular membrane and the associated cytochromes involved in electron transport. Oxidation of the substrate is followed with a respirometer or with oxygen electrodes. Both these methods are complicated and expensive to set up and to maintain. Again, at our university, this technique appears to be appropriate for MS level graduate students. This test... 

Yeast is of exceptional value in the study of cytochrome regulation. It is a facultative anaerobe, and the usual cytochromes disappear under anaerobic conditions. On aeration, cytochrome induction can be demonstrated in the living cell, and the role of oxygen and carbon source, as well as the effect of inhibitors, can be evaluated by a variety of means [19-25], Yeast affords opportunities for genetic analysis and lends itself to studies of the inheritance of nuclear factors governing cytochrome synthesis. Moreover, this organism readily develops a mitochondrial abnormality on treatment with acriflavine, the petite mutation, which permits examination of the role of cytoplasmic inheritance [26]. 

Another derepressive carbon source is melibiose, which was used in studies of mutants capable of achieving various levels of cytochrome c [37,39]. It was found that mutants low in cytochrome c are particularly sensitive with respect to glucose repression of cytochrome a. Diminished cytochrome a synthesis can, therefore, be a secondary effect of other cytochrome deficiences [37,39]. 

Oxidation of different substrates. We found (Vorobjeva, 1959) that glycerol can be used as a sole carbon source by P. jensenii only under aerobic conditions. If fumarate was added to minimal medium, then glycerol fermentation proceeded under anaerobic conditions with fumarate acting as an electron acceptor. Propionibacteria can oxidize compounds more reduced than glycerol, namely, alkanes and long-chain primary alcohols (Table 3.1). Oxidation of hydrocarbons is suppressed by the inhibitors of cytochrome oxidases, NaNa (10 M) and KCN (10" M), respectively, by 88 and 96%, which is similar to the degree of inhibition observed for glucose oxidation by P. pentosaceum. 

An excellent example of this is provided by cytochrome P450, an enzyme from Sphingomonas sp. HXN-200, which was shown to have good hydroxylation activity toward substrates such as N-benzyl heterocycles and terpenes in the wild-type strain [30,31 ]. One major disadvantage of the Sphingomonas is that it needs to be grown on the flammable hydrocarbon octane as the sole carbon source in order to induce expression of the P450 enzyme. 

Organisms which oxidize methane exclusively and use this substrate as a source of carbon and energy appear to be restricted to Methanomonas sp. The latter is a strict aerobe which presumably contains cytochromes (67). 

Alcaligenes hydrogenophilus 2 [NiFe] hydrogenases Cytoplasmic NAD reducing Membrane- bound cytochrome b reducing Energy conservation H2, carbon and energy source limitation 1... 

Carbon monoxide binds to cytochrome a/Oj but less tightly than cyanide. It also binds to hemoglobin, displacing oxygen. Symptoms include headache, nausea, tachycardia, and tachypnea. Lips and cheeks turn a cherry-red color. Respiratory depression and coma result in death if not treated by giving oxygen. Sources of carbon monoxide include ... 

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