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The metabolic network consists of enzymes and chemical compounds. However, a large number of metabolic pathways remain unknown, and many enzymes are missing even in known metabolic pathways. We employed biochemical and bioinformatic approaches to identify several missing enzyme genes in lysine degradation pathways in Pseudomonas. First, we purified and characterized a novel NADPH-dependent enzyme, N-methyl-L-amino acid dehydrogenase from P. putida. Biochemical and genetic studies redefined its physiological role as Δ^1 -piperideine-2-carboxylate reductase, a missing enzyme in the D-lysine degradation pathway. Second, we predicted several missing enzyme genes to reconstruct the lysine degradation pathway of P. aeruginosa and confirmed PA0266 as 5-aminovalerate aminotransferase and PA0265 as glutarate semialdehyde dehydrogenase. Finally, we predicted a gene for L-lysine-2-monooxygenase by comparing its amino acid composition data with those of all ORFs in the P. putida genome. A gene for 5-aminovaleramidase was found to locate adjacent to the L-lysine-2-monooxygenase gene in the genome.

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In this review, we summarize our recent reports: the roles of carnitine in the general metabolism and the central nervous system, and the effects of carnitine administration to the fasted carnitine-deficient juvenile visceral steatosis (JVS) mice. Fasting reduced locomotor activity (LA) of JVS mice. Single carnitine administration caused an increase of the reduced LA and the fat expenditure, and the effects were prolonged for at least two days after the administration, although the carnitine concentration in blood and tissues returned to the original carnitine-deficient level. In JVS mice, fasting also caused a decreased percentage of c-Fos positive orexin neurons in the lateral hypothalamus (ameliorated by carnitine administration) and a reduced orexin-A concentration in the cerebrospinal fluid. These results suggest that the low tissue carnitine level of JVS mice is not the sole rate-limiting factor of general fatty acid oxidation, and the reduced LA in fasted JVS mice is related to the inhibition of orexin neuronal activity.

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Arachidonic acid (ARA) is a major constituent of cell membranes, and thus plays important roles in the preservation of physiological and psychological function. In 1993, it has been reported that ARA status correlates with first year growth in preterm infants. A randomized controlled trial of early dietary supply of long-chain polyunsaturated fatty acids and mental development in term infants has been carried out in 2000, showing that not only docosahexaenoic acid (DHA) but also ARA are necessary for the brain development. Moreover, it has been shown that age-related decline of ARA content in brain and brain function estimated by long-term potentiation (LTP) were reversed by dietary supply of ARA. We investigated the effect of ARA supplementation on aspects of brain function of elderly people by the measurement of the electroencephalogram of event related potentials, P300. In subjects administered ARA-enriched triglyceride capsules, P300 latency became significantly shorter and P300 amplitude slightly increased compared with those administered olive oil capsules. From these data it can be concluded that ARA is essential for human, particularly for infants and elderly people.

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