Antenatal Bartter's syndrome: why is this not a lethal condition?

There are four themes in this teaching exercise for Professor McCance. The first challenge was to explain how a premature infant with Bartter's syndrome could survive despite having such a severe degree of renal salt wasting. Second, the medical team wanted to know why there was such a dramatic decrease in the natriuresis in response to therapy, despite the presence of a permanent molecular defect that affected the loop of Henle. Third, Professor McCance was asked why this patient seemed to have a second rare disease, AQP2 deficiency type of nephrogenic diabetes insipidus. The fourth challenge was to develop a diagnostic test to help the parents of this baby titrate the dose of indomethacin to ensure an effective dose while minimizing the likelihood of developing nephrotoxicity. The missing links in this interesting story emerge during a discussion between the medical team and its mentor.

High guanine plus cytosine content in the third letter of codons of an extreme thermophile. DNA sequence of the isopropylmalate dehydrogenase of Thermus thermophilus.

In studies on the cause of the extreme stability of the macromolecules of Thermus thermophilus HB8, the leuB gene coding for 3-isopropylmalate dehydrogenase of the leucine synthesis pathway and its flanking regions were cloned and sequenced. The leuB gene of T. thermophilus was expressed in a leuB-less mutant of Escherichia coli, and thermostable dehydrogenase was purified from an extract of the cells. The primary structure of the thermophilic isopropylmalate dehydrogenase was deduced from the nucleotide sequence leuB gene (1017 base pairs) and the amino acid sequence of the peptides isolated from the purified dehydrogenase. The thermophilic dehydrogenase has Mr = 35,968, and the value was close to that determined for the monomer of dehydrogenase (36,000) by gel electrophoresis. The molecular weight of active dimeric dehydrogenase was found to be 73,000 by high speed liquid chromatography. The primary structure of dehydrogenase was consistent with the amino acid composition of the dehydrogenase. In contrast to the isopropylmalate dehydrogenase of E. coli which contains 8 cysteine residues, there was no cysteine in thermophilic isopropylmalate dehydrogenase. The 5'-noncoding region contained a typical Shine-Dalgarno sequence. The guanine plus cytosine content of the coding region was 70.1%, and that of the third letter of the codons was extremely high (89.4%).

Hybrid ATPase's formed from subunits of coupling factor F1's of Escherichia coli and thermophilic bacterium PS3.

ATPase complexes were reconstituted from homologous and heterologous combinations of alpha, beta, and gamma subunits of coupling factor ATPase TF1 of thermophilic bacterium PS3 and EF1 of Escherichia coli. TF1 and alpha beta gamma complex reconstituted from TF1 subunits were thermostable and activated by methanol, sodium dodecyl sulfate and anions and they were halophilic, whereas EF1 and its three-subunit complex did not show these properties. The hybrid ATPase alpha T beta T gamma E (complex of the alpha and beta subunits of TF1 and the gamma subunit of EF1) showed closely similar properties to TF1 except for thermostability, while alpha E beta E gamma T (alpha and beta from EF1 and gamma from TF1) had similar properties to EF1. These results suggest that alpha and/or beta is required for the properties of F1. The complex alpha E beta T gamma E showed similar properties to EF1 except for its optimum pH: this complex had a broad pH optimum at about pH 7, whereas EF1 had an optimum at pH 8.5. No hybrid complexes were thermostable, suggesting that all three subunits of TF1 are required for heat stability. These hybrids showed higher halophilicity than EF1, although they were less halophilic than TF1. The hybrid enzymes studied here are the first thermophilic-mesophilic hybrid enzymes obtained.