Identification, expression, and characterization of Escherichia coli guanine deaminase.

Using the human cDNA sequence corresponding to guanine deaminase, the Escherichia coli genome was scanned using the Basic Local Alignment Search Tool (BLAST), and a corresponding 439-residue open reading frame of unknown function was identified as having 36% identity to the human protein. The putative gene was amplified, subcloned into the pMAL-c2 vector, expressed, purified, and characterized enzymatically. The 50.2-kDa protein catalyzed the conversion of guanine to xanthine, having a K(m) of 15 microM with guanine and a k(cat) of 3.2 s(-1). The bacterial enzyme shares a nine-residue heavy metal binding site with human guanine deaminase, PG[FL]VDTHIH, and was found to contain approximately 1 mol of zinc per mol of subunit of protein. The E. coli guanine deaminase locus is 3' from an open reading frame which shows homology to a bacterial purine base permease.

Argininosuccinic aciduria: long-term treatment with arginine.

The presentation and 2 year treatment of a patient with argininosuccinic aciduria is reported. Erythrocyte argininosuccinate lyase activity was less than 2% of normal. Long-term management included protein restriction and arginine dietary supplementation. The child experienced three episodes of hyperammonaemia (greater than 100 microns), the first at birth, the second at 6.5 months and the third at 16 months. Neurological development deteriorated between 14 and 24 months. Hepatomegaly and biochemical hepatitis, a feature of this condition, was accompanied by enlarged mitochondria with tubular paracrystalline inclusions not previously recognized in this disorder.