Evidence for ligand-induced conformational changes in proteins from phosphorescence spectroscopy

Phosphorescence spectroscopy on mouse myeloma IgA J539 in rigid solution at 77K revealed the type of anomalous short-lived component in the tryptophan decay originally observed with lysozyme (Churchich, J.E., 1966. Biochim. Biophys. Acta. 120:406-412) and seen in a large number of Bence Jones proteins (Longworth, J.W., C.L. McLaughlin, and A. Solomon. 1976. Biochemistry. 15:2953-2958). The decay time of the anomalous component that results from the interaction between tryptophan side chains and disulfide linkages in proteins was observed to significantly lengthen in J539 in response to binding of a galactan antigen. With hen egg-white lysozyme in which the type of fluorescence enhancement on ligand binding seen with J539 has also been observed, phosphorescence measurements revealed a similar lengthening of the decay time of the disulfide-induced anomalous component in the tryptophan decay. These perturbations are interpreted as ligand-induced changes to the tryptophan-disulfide proximities that have been shown to exist in these structures. Given the short-range nature of the disulfide perturbation (see following article) the observations suggest, in particular when combined with x-ray crystallographic data, that phosphorescence decay-time measurements of disulfide perturbations can serve as a sensitive spectroscopic indicator of subtle conformational changes in immunoglobulins and other tryptophan-disulfide containing proteins.

Distance dependence of the tryptophan-disulfide interaction at the triplet level from pulsed phosphorescence studies on a model system

In the present study the distance dependence of tryptophan-disulfide interaction is examined with a view to both utilizing the interaction as a more quantitative indicator of subtle conformational changes in proteins as well as elucidating the interaction mechanism. To examine perturbations specifically at the indole triplet level 2-(3-indolyl)-ethyl phenyl ketone (IEPK) in which excitation is transferred with high efficiency to the triplet state of the indole moiety was employed. Phosphorescence decays of IEPK excited by a laser pulse in 70/30 (vol/vol) ethanolether at 77 K were measured in the presence of various concentrations of simple disulfides. The nonexponential phosphorescence decays arising from a distribution of fixed chromophoreperturber separations and the steady-state quenching of IEPK were accounted for with an exponential dependence of the quenching rate constant with distance. The small effective Bohr radius (0.8 A) that appears in the exponent emphasizes the localized nature of the interaction. Comparison of the triplet quenching rate constant obtained at quencher contact with IEPK to that estimated in proteins suggests a dependence on the triplet energy of the indole moiety and an endothermic nature for the quenching process. The study predicts that in proteins tryptophan-disulfide interactions are very localized in nature and should give rise to detectable anomalous decays only out to 2 A beyond van der Waals contact between the interacting partners.

Cerebral blood flow and metabolism in severely head-injured children. Part 1: Relationship with GCS score, outcome, ICP, and PVI

The literature suggests that in children with severe head injury, cerebral hyperemia is common and related to high intracranial pressure (ICP). However, there are very few data on cerebral blood flow (CBF) after severe head injury in children. This paper presents 72 measurements of cerebral blood flow ("CBF15"), using the 133Xe inhalation method, with multiple detectors over both hemispheres in 32 children aged 3 to 18 years (mean 13.6 years) with severe closed head injury (average Glasgow Coma Scale (GCS) score 5.4). In 25 of the children, these were combined with measurements of arteriojugular venous oxygen difference (AVDO2) and of cerebral metabolic rate of oxygen (CMRO2). In 30 patients, the first measurement was taken approximately 12 hours postinjury. In 18 patients, an indication of brain stiffness was obtained by withdrawal and injection of ventricular cerebrospinal fluid and calculation of the pressure-volume index (PVI) of Marmarou. The CBF and CMRO2 data were correlated with the GCS score, outcome, ICP, and PVI. Early after injury, CBF tended to be lower with lower GCS scores, but this was not statistically significant. This trend was reversed 24 hours postinjury, as significantly more hyperemic values were recorded the lower the GCS score, with the exception of the most severely injured patients (GCS score 3). In contrast, mean CMRO2 correlated positively with the GCS score and outcome throughout the course, but large standard deviations preclude making predictions based on CMRO2 measurements in individual patients. Early after injury, there was mild uncoupling between CBF and CMRO2 (CBF above metabolic demands, low AVDO2) and, after 24 hours, flow and metabolism were completely uncoupled with an extremely low AVDO2. Consistently reduced flow as found in only four patients; 28 patients (88%) showed hyperemia at some point in their course. This very high percentage of patients with hyperemia, combined with the lowest values of AVDO2 found in the literature, indicates that hyperemia or luxury perfusion is more prevalent in this group of patients. The three patients with consistently the highest CBF had consistently the lowest PVI: thus, the patients with the most severe hyperemia also had the stiffest brains. Nevertheless, and in contrast to previous reports, no correlation could be established between the course of ICP or PVI and the occurrence of hyperemia, nor was there a correlation between the levels of CBF and ICP at the time of the measurements. The authors argue that this lack of correlation is due to: 1) a definition of hyperemia that is too generous, and 2) the lack of a systematic relationship between CBF and cerebral blood volume

[A study of the quality of Fujian native Magnolia officinalis Rehd. et Wils. var. biloba Rehd. et Wils]

This study reports on the connexion of the content of the efficacious constituents, magnolol and honokiol of Magnolia officinalis var. biloba with age, diameter of the trunk and various parts of the tree, thus presenting a basis for its collection, quality control and clinical applications.

A live cell enzyme-linked immunosorbent assay for detecting human hepatoma membrane antigens

Live cell enzyme-linked immunosorbent (ELISA) and fixed cell indirect immunofluorescence (IF) assays were compared to screen mouse hybridomas producing immunoreactive monoclonal antibodies against cell membrane antigens expressed on Ha22T, a human hepatoma cell line. While performing live cell ELISA, two parameters were tested to improve the viability of the target cells. The first parameter was the inclusion of growth medium in the assay buffers, and the second was performing the assay incubations at 37 degrees C in an incubator containing 5% CO2 in the air. Fixed cell IF detected and classified 46% of the hybridomas secreting monoclonal antibodies reactive with membrane, cytoplasm, cytoskeleton, and nuclear antigens of Ha22T cells. Fixed cell IF was able to reveal mixtures of two or more hybridomas growing in the same well secreting antibodies to different cell organelles. The live cell ELISA, on the other hand, identified 12 additional membrane reactive monoclonal antibodies from the hybridoma supernatants that were not reactive by IF. These results disclose that cell fixation procedures used for IF either completely or partially inactivated some of the cell membrane antigens. We, therefore, propose the use of a combination of immunoassays to select the maximum number of hybridomas secreting useful monoclonal antibodies from somatic cell fusions.

Production of new polyene antibiotics by Streptomyces cellulosae after addition of ethyl (Z)-16-phenylhexadec-9-enoate

Ethyl (Z)-16-phenylhexadec-9-enoate (3), an analog of ethyl oleate (2), was synthesized and added to cultures of Streptomyces cellulosae ATCC 12625 which normally produce fungichromin (1) as the principal polyene antibiotic. These cultures showed drastic reduction of fungichromin biosynthesis but afforded four new polyene antibiotics with a truncated four carbon side chain which are designated as isochainin (11) (an isomer of chainin (10], 14-hydroxyisochainin (12), 1'-hydroxyisochainin (13), and 1',14-dihydroxyisochainin (14). The close correspondence of 13C NMR chemical shifts between these compounds and fungichromin suggests that the stereochemistry at every site is exactly analogous.

[Protective effects of the pollen of Codonopsis pilosula (Franch.) Nannf. on liver lesions at the ultrastructural level]

The experimental hepatic lesion of C57 mice was induced by carbon tetrachloride (CCI4), and the feeds containing pollen of Codonopsis pilosula were given to the animals. It was found by electronic microscopy that these pollens evidently reduced the hepatic steatosis, improved liver necrosis, suppressed the formation of the collagen fibrils in Disse's spaces and around central veinules. It was shown that the pollens of Codonopsis pilosula could counteract efficiently the liver lesion of mice induced by CCI4.

Monte Carlo-minimization approach to the multiple-minima problem in protein folding

A Monte Carlo-minimization method has been developed to overcome the multiple-minima problem. The Metropolis Monte Carlo sampling, assisted by energy minimization, surmounts intervening barriers in moving through successive discrete local minima in the multidimensional energy surface. The method has located the lowest-energy minimum thus far reported for the brain pentapeptide [Met5]enkephalin in the absence of water. Presumably it is the global minimum-energy structure. This supports the concept that protein folding may be a Markov process. In the presence of water, the molecules appear to exist as an ensemble of different conformations.

Neural tube defects in Beijing-Tianjin area of China. Urban-rural distribution and some other epidemiological characteristics

Records in the obstetric wards and nurseries of 18 hospitals were reviewed and studied epidemiologically, covering about 210,000 deliveries and 1000 cases of neural tube defects (NTD). All live and still births occurred in the period 1970-84. Following the NTD classification used by Koch (1984), our case series consisted of anencephalus 50.3%, spina bifida 44.2%, and NTD with other system defects 5.5%. Overall NTD prevalence rate at birth was 4 per thousand, obviously higher than those in most other countries. Marked urban-rural differences in NTD prevalence rate at birth were observed. The rate in rural areas after correction for selection bias was still as high as 7.25 per thousand. As compared with cities and suburbs, the relative risk of NTD born to mothers in rural regions was 2.4. The male-to-female ratios were much less than 1 for various kinds of NTD. Looking at the effect of maternal age and birth order simultaneously in 12 different settings, it can be seen that prevalence of NTD was moderately higher among second and third births to women aged less than or equal to 24 and those greater than or equal to 35 years of age.

Muscarinic action of acetylcholine in the pigeon optic tectum

Eighty visual units were extracellularly recorded from the pigeon optic tectum, and the effects of iontophoretically applied acetylcholine and its antagonists, atropine and tubocurarine, on these units were examined. The results showed that acetylcholine in the avian tectum functions as an excitatory transmitter or modulator and acts predominantly through a muscarinic mode of action.