This review article presents the biosynthesis, metabolism, sources, levels, and general functions of carnitine. Emphasis is placed on the expression of carnitine deficiency and insufficiency as well as the causes of these conditions. The various functions of carnitine are discussed as they may relate to disease treatment. (J Child Neurol 1995;10(Suppl):2S3-2S7).

Several lines of evidence are presented that an entity is present in mitochondria which converts lysine and carbamylphosphate to homocitrulline, distinct from the ornithine transcarbamylase (OTC): lack of inhibition by lysine of OTC with ornithine as substrate at the pH of the mitochondrial matrix, a K(m) for lysine of 6.3 mmol/l in the crude mitochondrial extract, versus a K(m) of 55.3 mmol/l after partial purification of OTC, decrease of the specific activity of OTC with lysine as substrate and increase of the specific activity with ornithine as substrate after heat denaturation, and separation of the activities for ornithine and lysine after isoelectric focusing. This would explain the excretion of homocitrulline in the HHH-syndrome, saccharopinuria, citrullinemia and hyperlysinemia. The fact that homocitrulline excretion is not observed in OTC deficiency suggests that the activity responsible for homocitrulline excretion is closely related to OTC.

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Blood plasma testosterone concentrations were significantly negatively correlated (r = -0.91, P<0.05) with blood plasma carnitine concentrations among dairy bulls of varying fertility levels. Blood plasma testosterone was positively correlated with spermatozoa total carnitine (r = 0.32), spermatozoa acylcarnitines (r = 0.35), and sperm motility (r = 0.49), whereas blood plasma carnitine concentration was negatively correlated with spermatozoa acylcarnitines (r = -0.48), spermatozOa total carnitine (r = -0.36), and sperm motility (r = -0.39). Furthermore, the concentrations of total carnitine (r = 0.67), free carnitine (r = 0.75), and acylcarnitines (r = 0.60

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