Structural and spectroscopic characterization of exogenous ligand binding to isolated factor F430 and its configurational isomers

Binding of axial ligands to the nickel(II) of isolated factor F430 from the methyl reductase enzyme of Methanobacterium thermoautotrophicum is demonstrated. Evidence of bis-ligand coordination is obtained from the x-ray absorption, optical, and resonance Raman spectral characterization of F430 and its 12,13-diepimeric isomer in the presence of a large excess of cyanide, pyridine, or 1-methylimidazole. Significant broadening and 5-10-nm red shifts of the main 430-nm optical absorption band and shifts of up to 30 cm-1 for the high-frequency Raman lines are observed upon coordination of these axial ligands. The Raman spectra of native F430 and the diepimer with a particular axial ligand are nearly identical. Nickel x-ray absorption edge spectra of the diepimer in the absence and presence of these exogenous ligands are indicative of conversion from a square-planar to a tetragonally distorted octahedral geometry. Analyses of the nickel extended x-ray absorption fine structure data for the ligated diepimer complexes yield detailed structural information for these complexes. Implications of these data with respect to the enzymatic mechanism and the structure of the enzyme-bound factor are discussed.

Structural heterogeneity and purification of protein-free F430 from the cytoplasm of Methanobacterium thermoautotrophicum

F430 is the nickel containing tetrapyrrole cofactor of S-methyl coenzyme M methylreductase, the enzyme that catalyzes the final step of methane production by methanogenic bacteria: the reduction of S-methyl coenzyme M (H3CSCH2CH2SO3-) to methane and coenzyme M (HSCH2CH2SO3-). The protein-free F430 obtained from the cytosol of Methanobacterium thermoautotrophicum, strain delta H, exists predominantly in two isomeric forms that differ in relative stereochemical disposition of acid side chains at the 12 and 13 positions of the macrocycle periphery (Pfaltz, A., Livingston, D. A., Jaun, B., Diekert, G., Thauer, R. K., and Eschenmoser, A. (1985) Helv. Chim. Acta 68, 1338-1358). A simple one-step chromatographic procedure for the large-scale separation of these isomers is described. X-ray absorption spectroscopic studies show that F430 (i.e. the native isomer) is 6-coordinate with long nickel-ligand bonds (approximately 2.1 A), suggesting an approximately planar macrocycle. In contrast, the 12,13-diepimer exhibits a 4-coordinate, square-planar structure with short nickel-nitrogen bonds (approximately 1.9 A), suggesting a ruffled macrocycle. Previous reports, based on other x-ray absorption spectroscopic data, of static disorder in F430 Ni-N distances are shown to be incorrect due to sample heterogeneity. The optical spectrum of F430 (whether purified from the protein-free cytosol or extracted at high ionic strength from the holoenzyme) differs significantly from that of the 12,13-diepimer. The optical spectral differences are correlated with the alterations in coordination number and geometry of the central nickel ion in the two F430 isomers.

Emphysematous pyelonephritis: a 5-year experience with 13 patients

Emphysematous pyelonephritis is a life-threatening necrotizing renal infection characterized by the production of gas. Of 8,105 admissions to our diabetes service during the last 5 years we identified 13 cases. The patients were managed aggressively with fluids and antibiotics, followed by immediate nephrectomy. The mortality rate is 40 to 50 per cent, primarily owing to sudden septic complications.

Variations in iron status with fatigue modelled from training in female distance runners

A low hemoglobin level or even frank anemia is common among female endurance runners; controversy presently exists on the effectiveness of iron supplementation. In the past inadequate descriptions of training and too infrequent measurement of iron indices over a sufficiently long period, have made it difficult to establish any relationship between iron status and training upon which to base a rational iron therapy. In this study 5 young women distance runners age 18-25 years have been studied for 300 days. A numerical index was used to quantify the extent of an individual's daily training effort and a conceptual model of the effect of training allowed definition of the extent of consequent fatigue, to be calculated. Red blood cell number and hemoglobin concentration were measured regularly throughout, and during the last 200 days serum iron, ferritin, total iron binding capacity and percent transferrin saturation were also measured. It has been shown in most subjects that serum iron and transferrin saturation varied in phase with training and the fatigue index, throughout the period while serum ferritin varied out of phase. It is suggested that supplementing iron intake may be of little use during heavy training and concomitant high fatigue because transferrin saturation is also very high at this time and ineffective in promoting absorption of dietary iron.

Catechol effect on the lysosomal enzymes in the adipose tissues of obese and obese-diabetic monkeys

The activities of three lysosomal hydrolases were assayed in the basal and isoproterenol-stimulated states in the adipose tissues of lean, obese and obese-diabetic monkeys. The basal activity of acid lipase appeared higher in the obese tissues with or without diabetes than in the lean tissue. Isoproterenol stimulation did not affect these activities. The basal activity of beta-galactosidase (beta-Gal) was similar in all tissues and unaffected by isoproterenol stimulation. Although basal activity of hexosaminidase (Hex) was comparable in all tissues, activity increased significantly in the stimulated diabetic-obese tissue but not in the stimulated tissues from lean animals or animals with simple obesity.

The course of development of glucose intolerance in the monkey (Macaca mulatta)

Longitudinal studies of the rhesus monkey reveal a syndrome of diabetes mellitus in those that become middle-aged and obese. The sequence of events in the development of the disease progresses from normoinsulinemia with normoglycemia through stages of hyperinsulinemia followed by below normal insulin levels with hyperglycemia and glycosuria. We believe the rhesus to be an excellent nonhuman primate model for maturity-onset diabetes in humans.

Social interaction and serum insulin values in the monkey (Macaca mulatta)

Social interaction studies were conducted with two groups of rhesus monkeys with abnormally elevated serum insulin values. In both studies, the animals that were lowest on the dominance-submissiveness scale showed a fall in insulin levels to within the normal range for the monkey. Upon removal from the group, insulin values in these animals returned to their previous elevated level. In neither instance was the fall in insulin level accompanied by fasting hyperglycemia.

Feeding behavior in monkeys with and without lesions of the hypothalamus

In monkeys (Macaca mulatta) without hypothalamic lesions, food intake was found to increase with increasing age and body weight; however, food intake per kilogram body weight showed a decline over the same period of time. As the animals became older, the amount of food intake converted to body weight decreased dramatically (feeding efficiency). Water intake was shown to be closely coupled to food intake. Both daily food and water-intake data were highly reliable over a period of years. Monkeys with ventromedial hypothalamic lesions exhibited hyperphagia and increased feeding-efficiency ratios and eventual obesity. The obese animals developed symptoms of diabetes mellitus. Animals with lesions restricted primarily to the arcuate nucleus showed no hyperphagia but increased feeding efficiency. These animals exhibited decreased growth hormone release and a transitory elevation of serum insulin.

Weight reduction and serum insulin levels in hypothalamic obese monkeys

Two hyperinsulinemic rhesus monkeys, made obsese (body weight 22 kg) by the placement of hypothalamic lesions, were place on a weight reduction diet for a period of approximately eight months. After losing approximately losing approximately 25% body weight, the animals exhibited a fall in serum insulin levels without changes in plasma glucose levels or composition of fat pad tissue. There was evidence that the number of adipocytes remained constant but were reduced in size after the body weight loss.

Feeding behavior in monkeys with spontaneous diabetes mellitus

In our laboratory, monkeys (Macaca mulatta) that attain middle age (10-14 years) and a body weight of over 15 kg often develop spontaneous diabetes mellitus. In some animals the development of the disease is accompanied by polyphagia and polydipsia. The polyphagia appears to be in response to loss of body weight. Gross estimates of energy balance in diabetic monkeys indicate that the daily maintenance cost (kcal) of diabetes is greater during the untreated phase of the disease than in the pre-diabetic state.