Normal fMRI brain activation patterns in children performing a verb generation task

Although much is known concerning brain-language relations in adults, little is known about how these functions might be represented during the developmental period. We report results from 17 normal children, ages 7-18 years, who have successfully completed a word fluency paradigm during functional magnetic resonance imaging at 3 Tesla. Regions of activation replicate those reported for adult subjects. However, a statistically significant association between hemispheric lateralization of activation and age was found in the children. Specifically, although most subjects at all ages showed left hemisphere dominance for this task, the degree of lateralization increased with age. This study demonstrates that fMRI can reveal developmental shifts in the pattern of brain activation associated with semantic language function.

Functional magnetic resonance imaging of the pediatric swallow: imaging the cortex and the brainstem

OBJECTIVE

To design and implement a functional magnetic resonance imaging (fMRI) protocol to investigate the cortical and brainstem patterns of activity in children with regard to the act of swallowing.

STUDY DESIGN

Pilot study to assess the clinical feasibility of the project.

METHODS

Using a 3T Bruker Biospec 30/60 MRI scanner, images were obtained using the Behavior Interleaved Gradient/Blood Oxygen Level Dependent (BIG-BOLD) image acquisition method. Initially, regions of interest (ROI) were developed to identify the mean time from the onset of a swallow to maximum cortical blood flow in the motor cortex. Using this data to design the BIG-BOLD acquisition method followed by postprocessing of the data, images from two volunteer adults and four volunteer children were obtained.

RESULTS

The average time from the onset of a swallow to maximum cortical blood flow was 6 to 8 seconds. Regions of cortical activity include pre- and post-central gyrus (Brodmann's areas 3 and 4), superior motor cortex (B.A. 24), insula, inferior frontal cortex (B.A. 44 and 45), Heschl gyrus (B.A. 41 and 42), putamen, globus pallidus, and the superior temporal gyrus (B.A. 38). Of particular note is the first mapping of the functional activity of swallowing at the level of the brainstem; activity was seen in the region of the nucleus ambiguous.

CONCLUSIONS

fMRI provides a novel means of studying the central processes of both normal swallowing and its various pathologic forms in children. Further understanding of how a child coordinates a swallow and how this coordination can be altered at the level of the brainstem and cortex may aid in the development of novel rehabilitative strategies.

Simultaneous correction of ghost and geometric distortion artifacts in EPI using a multiecho reference scan

A computationally efficient technique is described for the simultaneous removal of ghosting and geometrical distortion artifacts in echo-planar imaging (EPI) utilizing a multiecho, gradient-echo reference scan. Nyquist ghosts occur in EPI reconstructions because odd and even lines of k-space are acquired with opposite polarity, and experimental imperfections such as gradient eddy currents, imperfect pulse sequence timing, B0 field inhomogeneity, susceptibility, and chemical shift result in the even and odd lines of k-space being offset by different amounts relative to the true center of the acquisition window. Geometrical distortion occurs due to the limited bandwidth of the EPI images in the phase-encode direction. This distortion can be problematic when attempting to overlay an activation map from a functional magnetic resonance imaging experiment generated from EPI data on a high-resolution anatomical image. The method described here corrects for geometrical distortion related to B0 inhomogeneity, gradient eddy currents, radio-frequency pulse frequency offset, and chemical shift effect. The algorithm for removing ghost artifacts utilizes phase information in two dimensions and is, thus, more robust than conventional one-dimensional methods. An additional reference scan is required which takes approximately 2 min for a matrix size of 64 X 64 and a repetition time of 2 s. Results from a water phantom and a human brain at 3 T demonstrate the effectiveness of the method for removing ghosts and geometric distortion artifacts.

Three-dimensional MR microscopy of a transgenic mouse model of dilated cardiomyopathy

BACKGROUND

Scientists are now able to alter the genetics of vertebrate embryos routinely to produce animal models of human developmental diseases. However, our understanding of structural changes in these animal models is limited by current methodologies. Histological techniques, although providing great anatomic detail, display only "static" data (one time point only) in two dimensions. Ultrasound may be used to generate continuous time course data, but is limited by interobserver variation, limited acoustic windows, and relatively low resolution.

OBJECTIVE

To apply the high resolution, non-destructive, and three-dimensional acquisition capabilities of magnetic resonance (MR) microscopy to compare the hearts of normal mice versus an established transgenic mouse model of dilated cardiomyopathy.

MATERIALS AND METHODS

Transgenic mice exhibiting dilated cardiomyopathy were developed via the introduction of a mutated, heart-specific gene (myosin light chain). Postmortem cardiac imaging was performed on the transgenic mice and normal controls. MR imaging was performed on a Bruker 3T imaging magnet using a custom radiofrequency coil following contrast perfusion of the atrial and ventricular chambers. Image resolution was 156 microm isotropic voxels. MR images were compared to gross pathologic specimens. Imaging data were post-processed using custom software to calculate the volumes of the atria and ventricles and to display the three-dimensional morphology of the chambers and myocardium.

RESULTS

Of the seven mice scanned, four exhibited normal right atrial (average = 14.8 microl +/- 1.4), left atrial (average = 8.5 microl +/-0.3), right ventricular (average = 12.9 microl +/-2.7), and left ventricular (average 3.3 microl +/-0.5) volumes. Three mice exhibited dilatation of the right and left cardiac chambers (RA average = 23.9 microl +/-5.6; LA average = 15.9 microl +/-4.8; RV average = 32.5 microl +/- 6.8; LV average 24.0 microl +/-1.4). The gross morphology was verified upon autopsy of the animals and correlated with the animal's genotype. The differences in volumes between the normal and dilated cardiomyopathy mice were statistically significant (P values ranged from 0.001 to 0.024 for the different chambers).

CONCLUSION

MR microscopy is a potentially useful tool for developmental biology research. The imaging of mouse hearts is feasible, and these methods provide quantitative and qualitative morphologic data of a mouse model of dilated cardiomyopathy not available using traditional methods.

Perfusion imaging in the pediatric patient

The prevalence of cerebrovascular disease in children is much higher than most clinicians and neuroradiologists suspect, when all primary and secondary causes are considered. Most signal alterations found on MR imaging in childhood central nervous system pathologic conditions result from causes other than a decrease in tissue perfusion. In addition to conventional MR imaging, the ability to assess changes in tissue water by diffusion imaging and tissue perfusion by perfusion-weighted imaging can prove useful to asses cerebral hemodynamics in various pathologic disorders. Exogenous contrast bolus dynamic perfusion-weighted imaging is especially useful in children to differentiate between ischemic injury and other conditions that may alter T2 relaxation, such as demyelination and edema. Perfusion imaging has proved to be a robust and valuable tool to assess the hemodynamic component in childhood CNS disease related to neoplasms and complications from their therapy, cerebrovascular occlusive disease, childhood CNS arteriopathies and trauma.

fMRI of neuronal activation with symptom provocation in unmedicated patients with obsessive compulsive disorder

BACKGROUND

Previous studies suggest that a neural circuit involving over-activation of cortical, paralimbic, limbic, and striatal structures may underlie OCD symptomatology, but results may have been limited by medication use in those studies. To address this, we examined the effects of symptom induction on fMRI neural activation in medication-free patients with OCD.

METHODS

Seven outpatients with OCD were exposed to individually tailored provocative and innocuous stimuli during fMRI scans. Self-ratings of OCD symptoms were performed prior to each scan and after exposure to stimuli. Images were analyzed as composite data sets and individually.

RESULTS

Stimulus presentation was associated with significant increases in OCD self-ratings. Significant activation was demonstrated in several regions of the frontal cortex (orbitofrontal, superior frontal, and the dorsolateral prefrontal); the anterior, medial and lateral temporal cortex; and the right anterior cingulate. Right superior frontal activation inversely correlated with baseline compulsion symptomatology and left orbitofrontal cortical activation was inversely associated with changes in OCD self-ratings following provocative stimuli.

CONCLUSIONS

These results in unmedicated patients are consistent with those from previous studies with medicated patients and suggest that OCD symptomatology is mediated by multiple brain regions including the anterior cingulate as well as frontal and temporal brain regions.

Hypoglycemic brain injury: potentiation from respiratory depression and injury aggravation from hyperglycemic treatment overshoots

Hypoglycemia can cause brain dysfunction, brain injury, and death. The present study seeks to broaden current information regarding mechanisms of hypoglycemic brain injury by investigating a novel etiology. The cat's high resistance to brain injury from hypoglycemia suggested that additional influences such as respiratory depression might play a facilitating role. Three groups of cats were exposed to fasting and insulin-induced hypoglycemia (HG; n = 6), euglycemic respiratory depression (RD; n = 5), and combined hypoglycemic respiratory depression (HG/RD; n = 10). The HG animals were maintained at <1.5 mmol (mean 1 mmol) serum glucose concentration for 2 to 6.6 hours. The respiratory depression was associated with PaO2 and PaCO2 values of approximately 50 mm Hg for 1 hour and of approximately 35 and approximately 75 mm Hg, respectively, for the second hour. Magnetic resonance diffusion-weighted imaging estimated brain energy state before, during, and after hypoglycemia. The hypoglycemic respiratory depression exposures were terminated either to euglycemia (n = 4) or to hyperglycemia (n = 6). Brain injury was assessed after 5 to 7 days of survival. Cats exposed to hypoglycemia alone maintained unchanged diffusion coefficients; that is, they lacked evidence of brain energy failure and all six remained brain-intact. Only 1 of 5 euglycemic RD but 10 of 10 HG/RD cats developed brain damage (HG and RD vs. HG/RD, P < 0.01). This difference in brain injury rates suggests injury potentiation by hypoglycemia and respiratory depression acting together. Three injury patterns emerged, including activation of microglia, selective neuronal necrosis, and laminar cortical necrosis. Widespread activation of microglia suggesting damage to neuronal cell processes affected all damaged brains. Selective neuronal necrosis affecting the cerebral cortex, hippocampus, and basal ganglia was observed in all but one case. Instances of laminar cortical necrosis were limited to cats exposed to hypoglycemic respiratory depression treated with hyperglycemia. Thus, treatment with hyperglycemia compared with euglycemia after hypoglycemic respiratory depression exposures significantly increased the brain injury scores (24 +/- 6 vs. 13 +/- 2 points; P < 0.05). This new experimental hypoglycemia model's contribution lies in recognizing additional factors that critically define the occurrence of hypoglycemic brain injury.

NMR relaxation times in the human brain at 3.0 tesla

Relaxation time measurements at 3.0 T are reported for both gray and white matter in normal human brain. Measurements were made using a 3.0 T Bruker Biospec magnetic resonance imaging (MRI) scanner in normal adults with no clinical evidence of neurological disease. Nineteen subjects, 8 female and 11 male, were studied for T1 and T2 measurements, and 7 males were studied for T2. Measurements were made using a saturation recovery method for T1, a multiple spin-echo experiment for T2, and a fast low-angle shot (FLASH) sequence with 14 different echo times for T2. Results of the measurements are summarized as follows. Average T1 values measured for gray matter and white matter were 1331 and 832 msec, respectively. Average T2 values measured for gray matter and white matter were 80 and 110 msec, respectively. The average T2 values for occipital and frontal gray matter were 41.6 and 51.8 msec, respectively. Average T2 values for occipital and frontal white matter were 48.4 and 44.7 msec, respectively. ANOVA tests of the measurements revealed that for both gray and white matter there were no significant differences in T1 from one location in the brain to another. T2 in occipital gray matter was significantly higher (0.0001 < P < .0375) than the rest of the gray matter, while T2 in frontal white matter was significantly lower (P < 0.0001). Statistical analysis of cerebral hemispheric differences in relaxation time measurements showed no significant differences in T1 values from the left hemisphere compared with the right, except in insular gray matter, where this difference was significant at P = 0.0320. No significant difference in T2 values existed between the left and right cerebral hemispheres. Significant differences were apparent between male and female relaxation time measurements in brain.

NMR relaxation times in the human brain at 3.0 tesla

Relaxation time measurements at 3.0 T are reported for both gray and white matter in normal human brain. Measurements were made using a 3.0 T Bruker Biospec magnetic resonance imaging (MRI) scanner in normal adults with no clinical evidence of neurological disease. Nineteen subjects, 8 female and 11 male, were studied for T1 and T2 measurements, and 7 males were studied for T2. Measurements were made using a saturation recovery method for T1, a multiple spin-echo experiment for T2, and a fast low-angle shot (FLASH) sequence with 14 different echo times for T2. Results of the measurements are summarized as follows. Average T1 values measured for gray matter and white matter were 1331 and 832 msec, respectively. Average T2 values measured for gray matter and white matter were 80 and 110 msec, respectively. The average T2 values for occipital and frontal gray matter were 41.6 and 51.8 msec, respectively. Average T2 values for occipital and frontal white matter were 48.4 and 44.7 msec, respectively. ANOVA tests of the measurements revealed that for both gray and white matter there were no significant differences in T1 from one location in the brain to another. T2 in occipital gray matter was significantly higher (0.0001 < P < .0375) than the rest of the gray matter, while T2 in frontal white matter was significantly lower (P < 0.0001). Statistical analysis of cerebral hemispheric differences in relaxation time measurements showed no significant differences in T1 values from the left hemisphere compared with the right, except in insular gray matter, where this difference was significant at P = 0.0320. No significant difference in T2 values existed between the left and right cerebral hemispheres. Significant differences were apparent between male and female relaxation time measurements in brain.

Magnetic resonance imaging of microbubbles in a superheated emulsion chamber for brachytherapy dosimetry

This paper describes development of magnetic resonance imaging (MRI) techniques for three-dimensional (3D) imaging of a position-sensitive detector for brachytherapy dosimetry. The detector is a 0.5 l chamber containing an emulsion of halocarbon-115 droplets in a tissue-equivalent glycerin-based gel. The halocarbon droplets are highly superheated and expand into vapor microbubbles upon irradiation. Brachytherapy sources can be inserted into the superheated emulsion chamber to create distributions of bubbles. Three-dimensional MRI of the chamber is then performed. A 3D gradient-echo technique was optimized for spatial resolution and contrast between bubbles and gel. Susceptibility gradients at the interfaces between bubbles and gel are exploited to enhance contrast so microscopic bubbles can be imaged using relatively large voxel sizes. Three-dimensional gradient-echo images are obtained with an isotropic resolution of 300 microns over a 77 mm x 77 mm x 9.6 mm field-of-view in an imaging time of 14 min. A post-processing technique was developed to semi-automatically segment the bubbles from the images and to assess dose distributions based on the measured bubble densities. Relative dose distributions are computed from MR images for a 125I brachytherapy source and the results compare favorably to relative radial dose distributions calculated as recommended by Task Group 43 of the American Association of Physicists in Medicine.

A position-sensitive superheated emulsion chamber for three-dimensional photon dosimetry

A position-sensitive detector chamber is introduced for the three-dimensional (3D) dosimetry of photon-emitting brachytherapy sources. The detector is based on an extremely fine suspension of monochloropentafluoroethane droplets emulsified in a gel. The droplets are highly superheated at room temperature and their evaporation can be triggered by photon interactions, leading to the formation of microscopic bubbles. Thus, when photon-emitting brachytherapy sources are inserted into the detector, bubble distributions form around them, enabling visualization of the radiation field. The tissue-equivalent emulsifier gel is highly viscous and keeps the bubbles immobilized at the location of their formation. Bubbles can then be imaged by nuclear magnetic resonance or optical scanning techniques. After the imaging, the detector can be pressurized in order to recondense the bubbles to the liquid phase. In a few minutes, the device is annealed and ready to be used again for repeated measurements improving the counting statistics. The photon sensitivity of the monochloropentafluoroethane droplets was determined with highly filtered, quasi-monochromatic x-ray beams and radionuclide gamma sources. The air-kerma response presents a broad maximum at low energies, due to the relatively high effective atomic number of the halocarbon molecule. A prototype chamber was built and successfully tested: bubble distributions deriving from the insertion of a 125I source were imaged by means of a slice-selective 3D gradient-echo technique. These experiments confirm the potential and viability of this new approach to 3D photon dosimetry.

Proton MR spectroscopic characteristics of pediatric pilocytic astrocytomas

PURPOSE

We report the common characteristics of juvenile pilocytic astrocytomas revealed by proton MR spectroscopy.

METHODS

Eight children with pilocytic astrocytomas were studied with proton MR spectroscopy. The selected sampling volume was approximately 4 cm3, obtained from solid tumor. To localize the sampling volume, we used point-resolved spectroscopy (PRESS) and stimulated-echo acquisition mode (STEAM) techniques to acquire long- and short-TE spectra, respectively. Spectra from PRESS and STEAM sequences were processed using Lorentzian-to-Gaussian transformation and exponential apodization, respectively. For PRESS (2000/270) spectra, peaks of creatine, choline, N-acetylaspartate (NAA), and lactate resonances were integrated; for STEAM (2000/20) spectra, we measured the amplitude of the peaks at 3.2, 2.0, 1.3 and 0.9 ppm.

RESULTS

An elevated lactate doublet was observed in the PRESS spectra. The choline/NAA ratio was 3.40. The amplitude ratios of the lipid pattern (0.9, 1.3 and 2.0 ppm) to choline were all below one.

CONCLUSION

Despite the benign histology of the tumor, which generally lacks necrosis, a lactate signal was detected in all eight patients studied. A dominant lipid pattern was not observed.

19F NMR monitoring of in vivo tumor metabolism after biochemical modulation of 5-fluorouracil by the uridine phosphorylase inhibitor 5-benzylacyclouridine

A uridine phosphorylase inhibitor, 5-benzylacyclouridine (BAU), has been utilized as biochemical modulator of 5-fluorouracil (5-FU) anti-tumor activity in a murine tumor model. The effect of BAU on 5-FU metabolism has been evaluated using in vitro and in vivo 19F NMR spectroscopy. The analysis of the NMR data revealed an increased formation and retention of fluorouracil nucleotides and fluorouridine in colon 38 tumors treated with the regimen containing BAU and a reduction in 5-FU catabolites (alpha-fluoro-beta-ureidopropionic acid and alpha-fluoro-beta-alanine). In the normal tissues evaluated, the presence of BAU did not significantly alter the metabolism and presence of fluoropyrimidine species, indicating a more selective effect on tumor tissues. Therapy experiments on C57/BL6 mice bearing colon 38 tumor showed that the administration of 120 mg/kg BAU 30 min before 5-FU at 85 mg/kg, on a weekly basis, resulted in an increased antineoplastic effect compared to the same dose of 5-FU alone. A smaller dose of 5-FU (60 mg/kg) also administered 30 min after 120 mg/kg BAU caused a reduction in tumor growth similar to 5-FU alone. The addition of BAU to 5-FU (85 mg/kg) resulted in a slight increase, although statistically nonsignificant, in host toxicity without causing any toxic death during the chemotherapeutic treatment. 19F NMR spectroscopy is here shown to be a powerful technique to evaluate changes in the metabolism of fluoropyrimidines after the use of biochemical modulator and to allow a correlation between improved therapeutic response with the biochemical effects generated in tissues.

Imaging oxygen tension in liver and spleen by 19F NMR

19F NMR imaging of the perfluorocarbon emulsion Fluosol has been used to study regional variations in oxygen tension in rat liver and spleen. We have used the linear dependence of spin lattice relaxation rate (1/T1) on the partial oxygen pressure (pO2) of Fluosol to determine the oxygen tension in the reticuloendothelial system (RES) of the liver and spleen of male Sprague-Dawley rats which have received serial infusions of Fluosol. Oxygen tension maps have been computed from 19F NMR images using a calibration obtained for Fluosol in vitro at 37.5 degrees C. The spatial resolution of the pO2 maps computed using this technique is 1.2 x 1.2 mm in 3-mm thick slices. Calculations from in vivo pO2 maps indicate an average change in the median pO2 of the RES from 118 to 80 mmHg for (n = 7) rats breathing 95% O2 and 5% CO2 (carbogen) and air, respectively.

The compact domain conformation of human Glu-plasminogen in solution

A complete understanding of the accelerating mechanisms of plasminogen activation and fibrinolysis necessarily requires structural information on the conformational forms of plasminogen. Given the absence of high-resolution structural data on plasminogen the use of lower resolution approaches has been adopted. Two such approaches have previously indicated a compact conformation of Glu-plasminogen (Tranqui, L., Prandini, M., and Chapel, A. (1979) Biol. Cellulaire, 34, 39-42; Bányai, L. and Patthy, L. (1985) Biochim. Biophys. Acta, 832, 224-227) whereas a third has suggested a fairly extended conformation (Mangel, W., Lin, B. and Ramakrishnan, V. (1990) Science, 248, 69-73). Native Glu-plasminogen has been investigated using small-angle X-ray scattering (SAXS) experiments. It is concluded that this molecule in solution is compact (radius of gyration, RG 3.05 +/- 0.02 nm and maximum intramolecular distance, Im 9.1 +/- 0.3 nm) and that the data are consistent with the right-handed spiral structure observed using electron microscopy by Tranqui et al. (1979). A spiral structure of native plasminogen would have important implications for the conformational response of plasminogen to fibrin and concomitant stimulation of plasminogen activation.

Ultrasound tissue characterization of breast biopsy specimens

Results of measurements of ultrasound speed and absorption coefficients in the range 3 to 8 MHz in breast tissues at 37 C are reported and analyzed in attempts to identify a set of ultrasound parameters capable of discriminating normal, benign, and malignant tissues. We analyzed 118 tissue regions, comprising 47 normal, 55 benign, and 16 malignant by straight-line fitting of frequency dependence of attenuation. Data for ten additional regions, for a total of 128, became available and were added to the cohort when we subsequently fitted quadratic curves. Sound speed consistently emerged as the variable with greatest discriminating power, particularly for separating normal from benign and malignant tissue. Great difficulty was encountered in discriminating benign from malignant, even when the jackknife technique was used. More success was found with classification and regression trees (CART), although results were sensitive to assigned misclassification costs. Best results from straight-line fits were obtained when discriminating malignant from combined normal/benign data after randomly assigning 75 percent of the data to the learning set and 25 percent to the test set. Then, 23 out of 25 normal/benign and 4 out of 4 malignant cases in the test set were correctly classified. With quadratic fitting, best results were obtained in the three-class case--the false positive rate for malignancy was reduced to zero in the learning (0/31) and test (0/10) sets. Nevertheless, the false negative rate increased to 13 out of 31 (42 percent) in the learning set, while attaining zero (0/4) in the test set.

Savings estimate for a Medicare insured group

Estimates of the savings potential of a managed-care program for a Medicare retiree population in Michigan under a hypothetical Medicare insured group (MIG) are presented in this article. In return for receiving an experience-rated capitation payment, a MIG would administer all Medicare and employer complementary benefits for its enrollees. A study of the financial and operational feasibility of implementing a MIG for retirees of a national corporation involving an analysis of 1986 claims data finds that selected managed-care initiatives implemented by a MIG would generate an annual savings of 3.8 percent of total (Medicare plus complementary) expenditures. Although savings are less than the 5 percent to be retained by Medicare, this finding illustrates the potential for savings from managed-care initiatives to Medicare generally and to MIGs elsewhere, where savings may be greater if constraints are less restrictive.

Nuclear magnetic resonance signal from flowing nuclei in rapid imaging using gradient echoes

A theoretical description of the nuclear magnetic resonance (NMR) signal from flowing nuclei has been developed for rapid imaging sequences that use small flip angles and gradient refocused echoes. Both laminar and plug flow models have been considered and formulas derived relating mean image signal intensity to flip angle, pulse sequence repetition interval (TR), and flow velocity. It is shown that the rate of approach to steady-state conditions determines the degree of flow enhancement. Experimental measurements have been performed on a flow phantom in a whole-body NMR imaging system operating at 0.15 T using the spoiled FLASH sequence with different radiofrequency pulse flip angles and flow rates. There is excellent agreement between the experimental results and the theoretical predictions up to the onset of turbulence.

Identifying catastrophic psychiatric cases. Targeting managed-care strategies

Case management programs, a specialized form of utilization review (UR), focus their interventions on catastrophic cases, which comprise the minority of patients while accounting for the majority of costs. Many case management programs base their case identification and review criteria on diagnosis alone, although research has shown that it is a poor predictor of length of stay. Using claims data from a large nationwide insurer, the authors developed an empirical approach to identifying potentially catastrophic cases. The findings suggest that, in addition to diagnosis, other factors such as age and treatment setting contribute to long stays and high costs and thus should be used to identify catastrophic cases for case management interventions. Strategies to target case management programs must be considered not only in light of their impact on cost but on the quality of care for individual patients.

Structure and order of the protein and carbohydrate domains of prothrombin fragment 1

The three-dimensional structure of prothrombin fragment 1 has been determined by X-ray crystallography at 3.8 A resolution. The fragment is composed of a number of structural units, some of which are ordered while others are disordered. The ordered part of the structure includes a compact kringle unit, a helical domain and a carbohydrate chain. The kringle structure is organized around a close pair of buried disulfide bridges. One of its carbohydrate chains, that attached to Asn 101, is fully ordered, but the carbohydrate chain attached to Asn 77 appears to be disordered. The calcium binding unit is composed of a disordered part containing all ten gamma-carboxyglutamic acid residues and an ordered part forming the helical domain. The highly conserved residues Phe 41, Trp 42 and Tyr 45, which form a hydrophobic cluster on the first helix, interact around a crystallographic two-fold axis with the equivalent residues in another molecule to form a dimer in the crystal.

Vitamin K-dependent blood coagulation proteins form hetero-dimers

The later stages of the blood coagulation cascade are characterized by the presence of vitamin K-dependent proteins and their involvement in membrane-bound, multi-protein converting complexes with an essential requirement for calcium ions. Specific interactions between zymogens and activating enzymes have not yet been identified. Here we describe a crystallographic study of prothrombin fragment 1 (residues 1-156 of prothrombin) which indicates that vitamin K-dependent coagulation proteins have specific association sites that allow them to form hetero-dimers. The calcium-induced formation of a hetero-dimer between fragment 1 and factor X is demonstrated by cross-linking. Such hetero-dimers of vitamin K-dependent proteins could be significant in the coagulation system.

The possible DNA-binding nature of the regulatory proteins, encoded by spoIID and gerE, involved in the sporulation of Bacillus subtilis

The predicted polypeptide products of two genes, spoIID and gerE, which appear to be concerned in the regulation of spore formation in Bacillus subtilis have been compared by modelling methods with known DNA-binding proteins. The results indicate that both polypeptides may have DNA-binding properties and the conclusion is drawn that this may account for their regulatory action.