Biomedical subjects
Publications and source records attributed to L Kurz.
Human bone-forming osteoblasts are an excellent model to investigate the multiple functions of inorganic polyphosphates (polyP) for the following reasons: 1) they contain relatively high amounts of polyP and polyP-dependent enzymes; 2) they allow the study of both general and specific functions of these polymers, and 3) medically relevant results can be expected from these studies.
The ionization state and hydrogen bonding environment of the transition state analogue (TSA) inhibitor, carboxymethyldethia coenzyme A (CMX), bound to citrate synthase have been investigated using solid state NMR. This enzyme-inhibitor complex has been studied in connection with the postulated contribution of short hydrogen bonds to binding energies and enzyme catalysis: the X-ray crystal structure of this complex revealed an unusually short hydrogen bond between the carboxylate group of the inhibitor and an aspartic acid side chain [Usher et al. (1994) Biochemistry 33, 7753-7759]. To further investigate the nature of this short hydrogen bond, low spinning speed 13C NMR spectra of the CMX-citrate synthase complex were obtained under a variety of sample conditions. Tensor values describing the chemical shift anisotropy of the carboxyl groups of the inhibitor were obtained by simulating MAS spectra (233 +/- 4, 206 +/- 5, and 105 +/- 2 ppm vs TMS). Comparison of these values with our previously reported database and ab initio calculations of carbon shift tensor values clearly indicates that the carboxyl is deprotonated. New data from model compounds suggest that hydrogen bonds in a syn arrangement with respect to the carboxylate group have a pronounced effect upon the shift tensors for the carboxylate, while anti hydrogen bonds, regardless of their length, apparently do not perturb the shift tensors of the carboxyl group. Thus the tensor values for the enzyme-inhibitor complex could be consistent with either a very long syn hydrogen bond or an anti hydrogen bond; the latter would agree very well with previous crystallographic results. Two-dimensional 1H-13C heteronuclear correlation spectra of the enzyme-inhibitor complex were obtained. Strong cross-peaks were observed from the carboxyl carbon to proton(s) with chemical shift(s) of 22 +/- 5 ppm. Both the proton chemical shift and the intensity of the cross-peak indicate a very short hydrogen bond to the carboxyl group of the inhibitor, the C.H distance based upon the cross-peak intensity being 2.0 +/- 0.4 A. This proton resonance is assigned to Hdelta2 of Asp 375, on the basis of comparison with crystal structures and the fact that this cross-peak was absent in the heteronuclear correlation spectrum of the inhibitor-D375G mutant enzyme complex. In summary, our NMR studies support the suggestion that a very short hydrogen bond is formed between the TSA and the Asp carboxylate.
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The authors report a unique case that presented with hemodynamic abnormalities and severe bradycardia, necessitating the insertion of a temporary pacemaker, as well as metabolic disturbances, hematologic changes, and hepatic and renal dysfunction in an elderly individual owing to lithium intoxication. This case also demonstrates that these various serious side effects of lithium resolved with prompt recognition and discontinuation of lithium. Lithium should be used with extreme caution and frequent monitoring especially in the elderly.
1. The biotransformation of nafimidone, an imidazole-substituted anticonvulsant, has been studied by characterization of urinary metabolites in dogs, cynomolgus monkeys, baboons and man. 2. The biotransformation of nafimidone in these laboratory animals and man is initially very similar, in each case proceeding by reduction to the aliphatic alcohol metabolite, nafimidone alcohol or 1-[2-hydroxy-2-(2-naphthyl)ethyl]imidazole. 3. Further transformation of this metabolite involves oxidation in the naphthyl and imidazole functions, and/or conjugation. 4. The dog differs from the higher primates in that no metabolic modification of the naphthyl group takes place, the major metabolite in the dog being the O-beta-glucuronide of nafimidone alcohol. 5. In higher primates and man two isomers involving dihydroxylation in the naphthyl ring--1-[2-hydroxy-2-(5,6- or 7,8-dihydroxydihydro-2-naphthyl)ethyl]imidazole--were tentatively identified. These species alone showed evidence of an imidazole linked N-glucuronide of nafimidone alcohol. 6. The possible occurrence of stereoselective metabolism by the introduction of a chiral centre at C-9 in nafimidone alcohol was indicated in human urine by the presence of both epimers of the O-beta-glucuronide of nafimidone alcohol in a 2:1 ratio.
Lysosomal enzymes isolated from the slime mold Dictyostelium discoideum bind to the mannose 6-phosphate receptor which is present in many mammalian cells. While binding to the receptor suggests that the slime mold enzymes possess the same mannose 6-phosphate recognition marker as their mammalian counterparts, initial structural studies of the phosphorylated oligosaccharides have indicated that the phosphate is attached to high mannose-type units via an unusual phosphodiester linkage (Freeze, H.H., Yeh, R., Miller, A.L., and Kornfeld, S. (1983) J. Biol. Chem. 258, 14874-14879). To identify the components of the phosphodiester group we have isolated the phosphorylated high-mannose oligosaccharides from D. discoideum AX3 cells labeled with [2-3H]mannose or [6-3H]glucosamine and from the differentiation medium of unlabeled cells. The major phosphorylated species contain one or two phosphodiester groups and an average of 6 or 7 mannose residues. The phosphodiesters are relatively stable to both acid and base hydrolysis, but upon strong acid hydrolysis (conditions that completely hydrolyze the oligosaccharide) mannose 6-phosphate residues are liberated. Through a combination of techniques, including fast atom bombardment and direct chemical ionization mass spectrometry, it is shown that the mannose 6-phosphate residues of the intact oligosaccharide are diesterified to methyl groups. This indicates that slime mold possesses a different biosynthetic pathway for the formation of phosphorylated high mannose-type oligosaccharides than is utilized by higher organisms.
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We attempted to control the platelet count of a patient with primary thrombocytosis utilizing long-term plateletpheresis therapy. The patient previously could not be controlled with chemotherapy, because of rapid development of leukopenia. Although intensive pheresis at the rate of four to five procedures per week produced rapid lowering of the patient's platelet count, continued therapy at the rate of two to three procedures a week failed to maintain these counts, and platelets gradually rose to pretreatment levels. We conclude that while plateletpheresis can produce acute lowering of elevated platelet counts, the rate of platelet production in primary thrombocytosis may be too rapid to allow for long-term control by pheresis alone, utilizing an acceptable treatment schedule of one of three procedures per week.
Os odontoideum has recently been considered an acquired lesion of the second cervical vertebrae. This case documents the natural progression of the formation of os odontoideum and correlates it with a traumatic event. This is the first case reported in the literature.
The absorption, distribution, excretion, and metabolism of 14C-nafimidone, a novel anticonvulsant, have been studied in rats. Nafimidone was completely absorbed following single oral doses of 10 and 100 mg/kg. After both iv and oral administration, nafimidone was rapidly eliminated from plasma (t 1/2 about 5 min), with concomitant formation of a pharmacologically active, nonconjugated metabolite, nafimidone alcohol. Systemic clearance of nafimidone from plasma after iv administration was approximately 2 times higher than hepatic blood flow in rats, and the oral bioavailability was 15%. However, the AUC of nafimidone alcohol was 30% higher after oral administration of nafimidone than that after iv administration of nafimidone. It is likely that, given its pharmacological activity, nafimidone alcohol is the more important species pharmacologically. Distribution of nafimidone-related radioactivity was widespread with highest concentrations associated with liver, kidney, adrenals, and the gastrointestinal tract. Elimination of radioactivity from tissues was rapid and complete, except that retention was noted in arterial vessels and in the ocular melanin of pigmented rats. Determination of hepatic and brain levels of nafimidone and nafimidone alcohol showed no detectable levels of nafimidone in either tissue. However, levels of nafimidone alcohol in liver and brain were as much as 13-fold and 2-fold, respectively, higher than levels in plasma. After either iv or oral administration of 14C-nafimidone, approximately two-thirds of the radioactivity was recovered in urine. The major urinary metabolites of nafimidone after a 100 mg/kg dose were characterized and shown to be dihydroxydihydronaphthalene, substituted nafimidone alcohol, and the 1-beta-glucuronide of nafimidone alcohol.