Crystallographic study of coenzyme, coenzyme analogue and substrate binding in 6-phosphogluconate dehydrogenase: implications for NADP specificity and the enzyme mechanism.

BACKGROUND: The nicotinamide adenine dinucleotide phosphate (NADP)-dependent oxidative decarboxylase, 6-phosphogluconate dehydrogenase, is a major source of reduced coenzyme for synthesis. Enzymes later in the pentose phosphate pathway convert the reaction product, ribulose 5-phosphate, to ribose 5-phosphate. Crystallographic study of complexes with coenzyme and substrate explain the NADP dependence which determines the enzyme's metabolic role and support the proposed general base-general acid mechanism. RESULTS: The refined structures of binary coenzyme/analogue complexes show that Arg33 is ordered by binding the 2'-phosphate, and provides one face of the adenine site. The nicotinamide, while less tightly bound, is more extended when reduced than when oxidized. All substrate binding residues are conserved; the 3-hydroxyl of 6-phosphogluconate is hydrogen bonded to N zeta of Lys183 and the 3-hydrogen points towards the oxidized nicotinamide. The 6-phosphate replaces a tightly bound sulphate in the apo-enzyme. CONCLUSIONS: NADP specificity is achieved primarily by Arg33 which binds the 2'-phosphate but, in its absence, obscures the adenine pocket. The bound oxidized nicotinamide is syn; hydride transfer from bound substrate to the nicotinamide si- face is achieved with a small movement of the nicotinamide nucleotide. Lys183 may act as general base. A water bound to Gly130 in the coenzyme domain is the most likely acid required in decarboxylation. The dihydronicotinamide ring of NADPH competes for ligands with the 1-carboxyl of 6-phosphogluconate.

Physicians' perspectives of HMOs and marketing: implications and recommendations.

The authors compare physicians in HMOs and those not in HMOs in order to determine how HMOs have affected their practices. Physicians in HMOs see more patients per day, but receive less income per patient than physicians not in HMOs; however, both groups of physicians agree that HMOs have not changed marketing practices. In fact, both groups report uncertainty as to the best way to market their practice, and in their understanding of marketing. The physicians do agree that patient referrals are the most important means of patient acquisition; however, both groups report a surprisingly low use of patient questionnaires. Implications and recommendations for HMOs, physicians, and health care marketing researchers are discussed.

Large luteinized follicular cyst of pregnancy and puerperium.

The case we have reported is that of the largest luteinized follicular cyst of pregnancy and puerperium described. Histologically, distinct layers of both luteinized granulosa and theca cells were observed in this case, in contrast to those described previously. Nuclear atypia was prominent and appeared to be degenerative.

Myocarditis and hepatitis B virus.

Two patients with hepatitis B virus infection and myocarditis are reported. The implicated pathogenesis was an immune complex mechanism in one patient. Both patients presented with heart failure and arrhythmia which were controlled with conventional medical therapy. Echocardiography played an important role for early detection of left ventricular dysfunction. The efficacy and safety of corticosteroid therapy is still conjectural. Acute hepatitis B infection should be a differential diagnostic consideration in the etiology of acute myocarditis.

Peliosis of the spleen. Report of a case and review of the literature.

Peliotic lesions of the liver and spleen are rare and usually occur in patients with wasting diseases, such as tuberculosis and cancer, or in patients who have received treatment with anabolic-androgenic steroids. Peliosis appears grossly as blood-filled, cyst-like or nodular lesions, 1 to 5 mm in diameter, that are distributed throughout the parenchyma of the affected tissue but do not alter the size of the organ. Intraperitoneal rupture of a peliotic bleb can be fatal. Peliosis of the spleen usually occurs in conjunction with peliosis hepatis, but in this subject with myelofibrosis and myeloid metaplasia who underwent autopsy, the lesions were present only in the spleen.

Pancreatitis and Reye's syndrome.

A review of 18 cases of Reye's syndrome autopsied at Indiana University Hospital since 1970 was done to document pancreatic lesions associated with the syndrome. A spectrum of inflammatory lesions was identified and grouped into four categories: group 1, no changes; group 2, minimal microscopic changes; group 3, moderate changes, ie, focal necrosis, exudates, or congestion; and group 4, severe acute pancreatitis. Patients in group 4 often had clinical or laboratory data suggesting the onset of pancreatitis after hospitalization. Acute pancreatitis is associated with Reye's syndrome, and patients should be monitored for its development. Hypotension, hypocalcemia, and glucose lability may herald the onset of acute pancreatitis in these patients.

A simplified, colorimetric micromethod for xylose in serum or urine, with phloroglucinol.

We have developed a simplified xylose assay procedure that requires only 10 min and requires 50 microL of serum or 5 microL of urine. The reaction with phloroglucinol is more sensitive than the classic p-bromaniline color reaction, and requires only 4 min of heating for color development. A single reagent is mixed with the specimen directly, without prior protein precipitation. Analytical recovery of xylose added to serum was quantitative; precision studies resulted in a between-day coefficient of variation of 5.2%. Glucose, which has significant potential for interference in most other xylose procedures, reacts under the test conditions only to the extent of 70 mumol of apparent xylose per liter for a 5.5 mmol/L solution of glucose. The new procedure has been valuable in the assessment of malabsorption, especially in children and infants, where serum xylose is the preferred measurement.