Tetrahydrobiopterin (BH(4)) is a naturally occurring cofactor essential for critical metabolic pathways. Studies suggest that BH(4) supplementation may ameliorate autism symptoms; the biological mechanism for such an effect is unknown. To help understand the relation between central BH(4) concentration and systemic metabolism and to develop a biomarker of central BH(4) concentration, the relati...

Determination of serum ornithine carbamoyltransferase (EC 2.1.3.3) activity can be a valuable diagnostic tool in the detection of liver diseases involving cytolytic processes. I describe a micromethod for measuring this activity in serum, in which the reaction product, citrulline, is measured colorimetrically in the incubation mixture without prior deproteinization. To eliminate the interferenc...

1. The relationship between intramitochondrial and extramitochondrial ATP-utilizing systems and the intramitochondrial ATP/ADP ratio was studied in isolated rat-liver mitochondria. Citrulline synthesis was used as an intramitochondrial ATP-utilizing system, and glucose-6-phosphate synthesis as an extramitochondrial ATP-utilizing system. The intramitochondrial ATP/ADP ratio was manipulated in th...

Activation, recruitment, and effector function of T lymphocytes are essential for control of mycobacterial infection. These processes are tightly regulated in T cells by the availability of l-arginine within the microenvironment. In turn, mycobacterial infection dampens T cell responsiveness through arginase induction in myeloid cells, promoting sequestration of l-arginine within the local mili...

Previous investigations have shown that biotin deficiency in Streptococcus lactis 8039 is associated with the loss in ability to convert ornithine and carbamyl phosphate to citrulline (1). Although protein synthesis in the presence of biotin was found to be necessary to restore completely the ornithine-citrulline enzyme activity of the biotin-deficient cells (2), a preliminary report on the bio...

The generation of nitric oxide (NO) is largely responsible for the intracellular killing of Trypanosoma cruzi by activated macrophages. The present study was carried out to determine whether the production of NO by activated murine macrophages cultured in physiologic levels of arginine can be augmented by increasing the availability of arginine, the substrate for NO biosynthesis. Increased exog...

The amino acid arginine is the sole precursor for nitric oxide (NO) synthesis. We recently demonstrated that an acute reduction of circulating arginine does not compromise basal or LPS-inducible NO production in mice. In the present study, we investigated the importance of citrulline availability in ornithine transcarbamoylase-deficient spf(ash) (OTCD) mice on NO production, using stable isotop...