Spin-label techniques for monitoring macromolecular rotational motion: empirical calibration under nonideal conditions

Practical techniques are demonstrated for determining rotational correlation times of macromolecules from the first harmonic absorption electron spin reasonance spectra of tightly bound spin labels. The techniques are developed to compensate for such nonideal conditions as residual label motion, temperature dependence of rigid limit spectral parameters, and the presence of inhomogeneous line broadening. These effects are all shown to be of importance in monitoring the rotational motion of carbonmonoxyhemoglobin which is spin labeled with the tightly bound nitroxide label, 4-maleimido-2,2,6,6-tetramethylpiperidinyl-1-oxy. Spin-label interactions with other paramagnetic agents are also shown to produce spectral changes which are qualitatively similar to, but quantitatively different from, those resulting from increases in the rate of rotational motion.

Spin label detection of intermolecular interactions in carbonmonoxy sickle hemoglobin

With recently developed spin label techniques for monitoring macromolecular rotational motion, heme-liganded sickle cell hemoglobin in the presence of inositol hexaphosphate is shown to exhibit restricted motional freedom as compared to liganded normal adult human hemoglobin. This motional restriction is dependent on both hemoglobin concentration and temperature.

Tertiary structure variability within the quaternary states of hemoglobin: a spin label study

Using variable temperature techniques, the spin label spectral resolution of hemoglobin labeled at the beta93 cysteines with N-(1-oxyl-2,2,6,6-tetramethyl-4-piperidinyl)iodonacetamide has been greatly enhanced. The effects of different ligands, inositol hexaphosphate, pH and salt concentration upon spin labeled ferrous and ferric hemoglobin indicate that the beta chain tertiary structure exhibits considerable variability within the oxy and deoxy quaternary structures. From these studies ligand and spin state changes both appear to be of significance in producing structural changes; binding of inositol hexaphosphate then produces further structural changes secondary in amplitude.

Librational motion of an "immobilized" spin label: hemoglobin spin labeled by a maleimide derivative

The spin label Tempo-maleimide, when "immobilized" in hemoglobin, is shown to exhibit motional fluctuation whose amplitude and/or frequency depend on temperature and solution conditions. These motional fluctuations are observable by several electron spin resonance techniques. For desalted hemoglobin the fluctuations are detectable at approximately -15 degrees C using saturation transfer techniques and at approximately +25 degrees C using line-width measurements of normal absorption spectra. In ammonium sulfate precipitated hemoglobin, however, motional fluctuations are not detectable by either technique up to at least 40 degrees C. The most probable mechanism for spin-label motion appears to be either fluctuations in protein conformation which affect the label binding site or conformational transitions of the nitroxide ring itself. These motional fluctuations are shown to introduce a librational character to the overall label motion during hemoglobin rotational diffusion, with the librational motion significantly affecting the use of spin-label spectral shapes to calculate hemoglobin rotational correlation times.

A Comparison of Several Assay Procedures to Detect Penicillin Residues in Milk 1

Milk samples from six healthy cows that alternately received intramuscular injections and intramammary infusions of penicillin were analyzed for the presence of penicillin residues using the disc assay, cylinder plate, and Delvotest-P³ methods. Time required for complete removal of penicillin from milk of treated cows was determined with each of the three tests. The disc assay antibiotic test detected penicillin in only 75% of the milk samples in which penicillin was detected by the Delvotest-P method. The cylinder plate method detected penicillin in only 83% of the milk samples in which penicillin was detected by the Delvotest-P method. Also, the Delvotest-P method detected penicillin residues for a significantly longer (P < .01) time than either the disc assay or cylinder plate methods in milk from cows following intramuscular injections. Only once following intramuscular injection was penicillin residue found in milk beyond the manufacturer's recommended withholding time of four milkings, and that did not persist beyond the fifth milking. In milk from cows receiving intramammary infusions, the Delvotest-P method detected penicillin residues for a significantly (P < .01) longer period than the disc assay method, but not longer than the cylinder plate method. No antibiotic residue was ever detected by any of the three tests beyond the manufacturer's recommended milk withholding time of six milkings.

Persistence of antibiotics in milk from cows treated late in the dry period

Nineteen cows were treated via intramammary infusion at various times prior to calving with one of two dry cow antibiotic preparations (cloxacillin or penicillin). Milk samples from these cows after calving were analyzed for antibiotic residues by the Sarcina lutea cylinder plate method. Eight cows were treated with cloxacillin was detected in the milk of only two cows after calving and then for only one milking, so no problem should exist with cloxacillin if the manufacturer's recommendations are followed. Penicillin residues were not detected in milk samples taken from cows treated more than 9 days prior to calving with the dry cow penicillin preparation. However, seven of nine cows treated with penicillin up to 9 days prior to calving had detectable penicillin residues in the milk from treated quarters after calving. Only one cow had detectable penicillin residues longer than the manufacturer's recommended milk withholding time of 96 h, and this cow was treated only 3 days prior to parturition. Normal routine on a dairy farm and adherence to manufacturer's recommendations should result in no antibiotic residue problems in milk from cows treated during the dry period for mastitis control with either cloxacillin or penicillin.

Proliferation of renal interstitial cells following injury induced by ureteral obstruction

The proliferation of renal interstitial cells was studied by the use of tritiated thymidine incorporation following unilateral ureteral obstruction in the rabbit. There was a nonuniform response with significant increase in nuclear labeling in the obstructed kidney in all zones at 24, 48, and 72 hours following obstruction with the exception of the inner medulla where the counts at 24 and 48 hours were not significantly different from sham-operated controls. The major labeling occurred in interstitial fibroblasts. Within the zones of high labeling (cortex and outer medulla) these cells were separated by widening of the intersittial space. In the zone of low labeling (inner medulla) the interstitial cells maintained their normal spatial relationships.

Colonization of the intestinal tract of conventional mice with Candida albicans and treatment with antifungal agents

Conventional mice inoculated with Candida albicans per os were unable to maintain this organism in the intestinal tract as judged by decreasing numbers of yeast recoverable from feces. After inoculation with 10(7) cells/mouse, fecal counts ranged from 10(5) cells per g of feces to 5 x 10(3) cells per g of feces during a 12-day experimental period. Addition of various antibiotics to the drinking water did not result in any improvement in maintenance or stability of the gut population. A combination of X irradiation and administration of tobramycin or gentamicin, however, resulted in a stable population of C. albicans in the intestinal tract, with cell counts in the feces remaining constant at a level of about 10(6)/g of feces for a period of 10 to 15 days. The usefulness of this model in assessing the effect of experimental drugs on C. albicans infections of the gut was demonstrated by the fact that treatment with a new antifungal antibiotic (A9145), amphotericin B, 5-fluorocytosine, or nystatin resulted in a reduction in the fecal counts of C. albicans from experimentally infected animals.

The History and Development of Aviation Medicine

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