Serum creatinine concentration at the onset of uremia: higher levels in black males

We compared serum creatinine and blood urea nitrogen concentrations, estimated creatinine clearances and frequency of uremic symptoms at the start of chronic hemodialysis in all 20 black and 179 white males treated between 1969 and 1983. Serum creatinine concentrations were significantly higher in black males (16.5 +/- 5.9 mg/dl) than in white males (11.7 +/- 4.7 mg/dl; p = 0.016). There were no significant differences in blood urea nitrogen concentration, estimated creatinine clearance and frequency of uremic symptoms between the two groups. Blood urea nitrogen to serum creatinine ratios were lower in black males, (7.3 +/- 1.9) than in white males (11.4 +/- 3.8; p = 0.0001), and only one black male had a ratio greater than 10 compared to 60% of whites. We concluded that black males tend to have higher serum creatinine concentrations than white males at the onset of uremic symptoms, and that higher striated muscle creatinine production in black males and not lower renal function may be the cause.

Pheochromocytoma presenting as rhabdomyolysis and acute myoglobinuric renal failure

We report the case of a previously healthy young woman who presented with the sudden onset of rhabdomyolysis and myoglobinuric renal failure, requiring hemodialysis for 3 weeks. Common causes of rhabdomyolysis were ruled out; as renal function returned, severe hypertension was noted and a pheochromocytoma was diagnosed. We suggest that pheochromocytoma causes rhabdomyolysis and myoglobinuria via catecholamine-mediated vasoconstriction and skeletal muscle ischemia.

Oral estrogens decrease bleeding time and improve clinical bleeding in patients with renal failure

PURPOSE

A prolonged bleeding time is associated with platelet dysfunction and clinical bleeding in patients with renal failure. Parenteral estrogens have been shown to shorten the prolonged bleeding time in patients with chronic renal failure, although the mechanism of action is unknown. We conducted a study to evaluate the efficacy of oral conjugated estrogens in this setting.

PATIENTS AND METHODS

Four patients with renal failure, prolonged bleeding time, and clinical bleeding were given 50 mg of conjugated estrogen (Premarin) daily.

RESULTS

Bleeding time normalized in two cases and was reduced to less than 50% of the pretreatment value in one of the remaining two cases. Bleeding stopped in all patients within two days. Ten dialysis patients with prolonged bleeding time were randomized to a course of 50 mg of Premarin daily or placebo. The bleeding time in all five patients in the Premarin group normalized or decreased to below 50% of the pretreatment value after 7.0 +/- 4.2 days of therapy. The bleeding time did not normalize in the five patients treated with placebo. No side effects attributable to therapy were reported.

CONCLUSION

We conclude that orally administered conjugated estrogens effectively improve the bleeding tendency in patients with chronic renal failure.

An illustration of the use of isotopes: the biosynthesis of porphyrins

In this article, David Shemin, who is now in retirement, describes how in 1944 he ingested 66 g of 15N-labeled glycine in order to determine the half-life of hemoglobin and other blood proteins. The ramifications of the experiment led to the unravelling of the biosynthesis of porphyrins and the role of glycine and alpha-aminolevulinic acid in heme, vitamin B12 and chlorophyll synthesis.

On the impact on biochemical research of the discovery of stable isotopes: the outcome of the serendipic meeting of a refugee with the discoverer of heavy isotopes at Columbia University

As late as the 1930s, approaches to biochemical research not only were rather primitive, but a certain amount of mysticism still surrounded the biochemical events that occur in the living cell. To a great extent, this was due to the lack of techniques needed to uncover the subtle reactions in the living cell. In the early 1930s, an accidental meeting of two scientists revolutionized approaches in biochemical studies and led to the scientific explosion in molecular biology that has occurred during the last few decades. The dark political storm in Germany deposited Dr. Rudolf Schoenheimer on the New York shore, where he met Professor Urey, who recently had discovered "heavy" hydrogen. Schoenheimer suggested that biological compounds tagged with heavy atoms of hydrogen would enable investigators to follow their metabolic pathways. This intellectual leap revolutionized the thinking and design of experiments and made it possible to uncover the myriad reactions that occur in the living cell.

Mechanism of porphobilinogen synthase. Requirement of Zn2+ for enzyme activity

The role of metal ions in the mechanism of action of bovine liver porphobilinogen synthase was investigated. Studies with chelating agents were consistent with a requirement of metal ions for enzyme activity, and the use of 8-hydroxyquinoline-5-sulfonic acid suggested that Zn2+ was present in the enzyme. The low activity detected in metal-free apoporphobilinogen synthase was attributed to adventitious metal ions. Addition of Zn2+ to the apoenzyme completely restored enzyme activity if the essential sulfhydryl groups on the enzyme were first reduced with sulfhydryl reagents. It does not follow necessarily from this observation that Zn2+ forms a bond with a sulfhydryl group in the enzyme. However, we also observed that Zn2+ did not bind to the enzyme unless the essential cysteinyl residues were reduced. We have concluded that the octameric enzyme contains 4 g atoms of Zn2+/mol from our enzyme activity measurements and binding studies. Alkylation of the enzyme resulted in a marked reduction in the binding of Zn2+ to the enzyme. These observations are consistent with the suggestion that the interaction of the Zn2+ ions with the enzyme occurs with sulfhydryl groups at the active site. It appears that Zn2+ does not participate in substrate binding nor in the maintenance of the quaternary structure of the enzyme. Possible mechanistic roles for Zn2+ in porphobilinogen synthase are discussed. It should be noted that Cd2+ was the only other element found which restored activity to the apoenzyme.

Quaternary structure of delta-aminolevulinic acid synthase from Rhodopseudomonas spheroides

Delta-Aminolevulinic acid synthase (succinyl-CoA: glycine C-succinyltransferase (decarboxylating) EC 2.3.1.37) was purified from Rhodopseudomonas spheroides. The purity of the enzyme preparation was established by its behavior in disc electrophoresis in the presence and absence of sodium dodecyl sulfate and by analytical ultracentrifugation. The molecular weight of the enzyme as determined by sedimentation equilibrium was found to be about 80,300, a value similar to those obtained by gel filtration, polyacrylamide gel electrophoresis, and sucrose gradient centrifugation. The molecular weight of the enzyme, denatured with either sodium dodecyl sulfate or guanidine hydrochloride, was found to be about 45,000 and 41,000, respectively. The dimeric structure was supported by sedimentation in sucrose gradients. Further evidence for the dimetic nature of the enzyme was obtained by gel electrophoresis of the enzyme treated with dimethylsuberimidate and sodium dodecyl sulfate.

Dissociation and reassociation of immobilized porphobilinogen synthase: use of immobilized subunits for enzyme isolation

The dissociation and association of an immobilized preparation of the octameric enzyme porphobilinogen synthase [5-aminolevulinate hydro-lyase (adding 5-aminolevulinate and cyclizing), EC 4.2.1.24] is described. On treatment of the immobilized preparation with 4 M urea, four subunits per octamer are removed which can be reassociated into a soluble octameric enzyme. The tetrameric bound residual protein can also be reassembled into an octameric structure, with the same initial enzyme activity, by exposing the residual bound protein to a soluble pure enzyme preparation or to a crude liver extract in the presence of urea. The dissociation of the reconstituted bound enzyme releases subunits that again can be reassembled into a soluble octameric pure protein even when the crude liver preparation is used as the donor of the subunits. Thus, a pure enzyme can be isolated in a reassociation-dissociation cycle. The use of immobilized preparations of oligomeric proteins is considered for intra- and interspecies hybridization studies and for the ready preparation of purified enzyme preparations from different species and is suggested as a model for study of the formation of an oligomeric enzyme in the presence of other polypeptides.

5-Aminolaevulinic acid dehydratase: structure, function, and mechanism

delta-Aminolaevulinic acid dehydratase catalyses the synthesis of porphobilinogen. The enzyme has a molecular mass of 285000 and is composed of eight similar subunits of molecular mass 35000. The N-terminal amino acid is acylated, and the number of peptides found on tryptic digestion equals the number of lysine and arginine residues per mass of 35000. The eight subunits are apparently arranged at the corners of a cube and therefore have dihedral (D4) symmetry. The bovine liver enzyme which has been cystallized contains 4--6 atoms of zinc per mole of enzyme. The apo-enzyme obtained on prolonged hydrolysis can be reactivated by the addition of zinc or cadmium ions. The dialysed enzyme must be first treated with dithiothreitol. There are two very active SH groups in a total of 6--7-SH groups per subunit. The substrate forms a Schiff base with the epsilon-amino group of a lysine residue. Reduction of the Schiff base with NaBH4 should reveal the number of active sites per mole of enzyme. It appears that only four of the eight subunits form a Schiff base with the substrate indicating that the enzyme exhibits the phenomenon of either half-site reactivity or negative cooperativity. The enzyme appears to have a strong subunit-subunit interaction for an immobilized preparation remained stable for at least a month. An immobilized enzyme preparation was treated in a manner so that it dissociated into tetramers. Both the eluate and protein still attached to the Sepharose on a column were enzymically active. The bound enzyme could not reassociate under assay conditions but still contained about 50% of the original enzyme activity. It would seem that the enzyme is active when composed with less than eight subunits.

The quaternary structure of delta-aminolevulinic acid dehydratase from bovine liver

The quaternary structure of delta-aminolevulinic acid dehydratase (5-aminolaevulinate hydrolyase, EC 4.2.1.24) from bovine liver was examined by analytical ultracentrifugation, polyacrylamide gel electrophoresis, and electron microscopy. The molecular weights, determined by sedimentation-velocity and sedimentation-equilibrium experiments, were 289,000 and 282,000, respectively. The molecular weight of the subunit in 6 M guanidine. HCl was 34,900 as determined by sedimentation-equilibrium and 35,000 as estimated by polyacrylamide gel electrophoresis. No evidence was obtained for the presence of a smaller polypeptide. It appears therefore that delta-aminolevulinic acid dehydratase from liver is composed of eight subunits. The molecules of the enzyme deposited in thin layers of negative stain were generally square with an edge length of 85-90 A. On the assumption that the subunits are spherical in shape with a diameter of 44 A and a density of 1.36 g/cm(3), the molecular weight of the octamer is calculated to be 292,000. The particles appear to consist of four discrete lobes arrayed at the four corners of a square. The above conclusion that the dehydratase possesses eight subunits can be readily reconciled with the appearance of the enzyme in the electron microscope if it is postulated that the eight subunits are arranged at the corners of a cube. Therefore, it would follow that the subunits are arranged with dihedral (D(4)) symmetry.