Oxygen utilization pathway

As stated in section 5.1.1, some bacteria derive energy from food sources without the use of oxygen, whereas others are able to use this gas. The pathway of oxygen utilization itself is also a stepwise series of reactions and thus the overall picture emerges of cellular metabolism characterized by multistep reactions. 

Both Kalckar and the Russians measured the ratio of atoms of phosphorus yielding ATP to the atoms of oxygen utilized (P/O ratio) and found values significantly greater than 1, the figure expected if a phosphate group had been introduced into a cycle intermediate, as in the glycolytic pathway. 

You are examining mitochondria from muscle cells of an infant who has a deficiency in one of the enzymes in the fatty acid oxidative pathway. The mitochondria consume oxygen normally when incubated with pyruvate and malate, "with succinate, or with palmitoyl CoA (in the presence of carnitine), but the rate of oxygen utilization is decreased when the mitochondria are incubated with linoleoyl CoA in the presence of carnitine. Blood levels of carnitine in the patient are low, while the levels of an unusual acylcami-tine derivative are present in blood and urine. Analysis of this acylcamitine species using mass spectroscopy reveals that it is trans-A, cis-A decadienoyl (C10 2)-acylcamitine. The infant suffers from hypotonia (lack of muscle tone) and slow weight gain. 

Zinc protoporphyrin IX is a normal metabolite that is formed in trace amounts during haem biosynthesis. However, in iron deficiency or in impaired iron utilization, zinc becomes an alternative substrate for ferrochelatase and elevated levels of zinc protoporphyrin IX, which has a known low affinity for oxygen, are formed. This zinc-for-iron substitution is one of the first biochemical responses to iron depletion, and erythrocyte zinc protoporphyrin is therefore a very sensitive index of bone-marrow iron status (Labbe et ah, 1999). In addition, zinc protoporphyrin may regulate haem catabolism by acting as a competitive inhibitor of haem oxygenase, the key enzyme of the haem degradation pathway. However, it has been reported... 

In summary, we may add that bacterial utilization of quinoline and its derivatives as a rule depends on the availability of traces of molybdate in the culture medium [363], In contrast, growth of the bacterial strains on the first intermediate of each catabolic pathway, namely, the lH-2-oxo or 1 II-4-oxo derivatives of the quinoline compound was not affected by the availability of molybdate. This observation indicated a possible role of the trace element molybdenum in the initial hydroxylation at C2. In enzymes, Mo occurs as part of the redox-active co-factor, and all the Mo-enzymes involved in N-heteroatomic compound metabolism, contain a pterin Mo co-factor. The catalyzed reaction involves the transfer of an oxygen atom to or from a substrate molecule in a two-electron redox reaction. The oxygen is supplied by the aqueous solvent. Certainly, the Mo-enzymes play an important role in the initial steps of N-containing heterocycles degradation. 

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