Computer simulation of the P31 NMR equations governing the creatine kinase reaction

A method for solving the Bloch equations that govern magnetization transfer NMR experiments is presented. It requires the numerical evaluation of a matrix exponential and lends itself to computer simulation. It is a simple, versatile method for evaluating P31-NMR magnetization transfer experiments designed to measure biochemical exchange rates. We apply the method to the saturation and inversion transfer experiments and find that the "initial slope" method of determining flux is subject to at least two interpretations. This verifies the accepted concept that biochemical models representing compartmentation and competing reaction hypotheses cannot be reliably distinguished by simply selecting values for NMR and biochemical parameters that give a "best fit" to experimental data. However, our results do indicate that a controlled manipulation of biochemical exchange rate may distinguish between these two models.     

利用数字图象技术观察蛋白质的结晶过程

用汽相扩散法生长溶菌酶晶体并利用ＣＣＤ显微摄像系统记录了溶菌酶晶体的生长过程。由此图象序列,我们可以计算晶体的最大线度、生长速度,估计溶菌酶分子层的增长速度,了解蛋白质晶体在结晶室内的分布及其形态变化。得到结果如下：蛋白晶体生长初期最大线度与时间近似成线性关系;各晶面生长速度基本相等。     

Mechanism for procaine-mediated hyperactivated motility in guinea pig spermatozoa

Hyperactivated motility was studied in guinea pig spermatozoa. In the presence of the local anesthetic procaine, a high number of sperm cells (64%) showed hyperactivation when incubated in minimal culture medium with pyruvate, lactate, and glucose. Hyperactivated motility was dependent on glucose in the medium. Sperm ATP concentration was increased twofold in hyperactivated sperm when compared to procaine-treated nonhyperactivated cells. cAMP levels were also higher in hyperactivated cells than in control spermatozoa. Thus, in living spermatozoa high levels of ATP appear to be needed to generate hyperactivation. cAMP is present at a high concentration in hyperactivated spermatozoa, therefore a role of cAMP in hyperactivation cannot be excluded. Depletion of external Ca²⁺ did not inhibit procaine-induced hyperactivated motility. Hence, procaine canceled the requirement of external Ca²⁺ for sperm to express hyperactivated motility. © 1994 Wiley-Liss, Inc.     

Experimental investigation of the elastic-plastic deformation of mineralized lobster cuticle by digital image correlation

This study presents a novel experimental approach to the characterization of the deformation of a mineralized biological composite using arthropod cuticle as a model material. By performing tensile tests combined with a detailed strain analysis via digital image correlation, the elastic-plastic deformation behavior of the endocuticle of the American lobster Homarus americanus is examined. The test specimens originate from the pincher and crusher claws. For evaluating the effect of moisture on the deformation behavior, the samples are tested both in dry and in wet state. Sample characterization using the digital image correlation method requires a stochastic spot pattern on the sample surface. Digital images are then taken at subsequent deformation stages during the mechanical test. These images are used to calculate the displacement, the displacement gradient, and the strain fields via pattern correlation. The method is applied both, at a global scale to measure with high precision the stress-strain behavior of the bulk cuticle and at a microscopic scale to reveal strain heterogeneity, strain patterning, and strain localization phenomena.     

Vegetal cover estimated by digital photographs related to biomass in a grassland site in northern Mexico

A regression model was used to determine the relationship between aerial herbaceous biomass and vegetation coverage estimated by digital images. Four samplings (n=36 each date) of vegetation cover and herbaceous biomass were performed during the growing season in 2011 in a grassland dominated by Bouteloua gracilis in La Cieneguilla, Municipality of Villa Hidalgo, Durango. Average production of dry biomass was 37.36 ± 9.66 g/m², and mean vegetation cover 30.02%. Dry biomass data were tested for normality using the test of Kolmogorov Smirnov, finding a lack of fit. The data were subjected to a logarithmic transformation and the model Ln(y) = 1.637926 + 0.08501X - 0.000586X² with an adjusted R² = 0.89 was found. In order to validate this model, another five samplings were carried out in 2013 at the same site during summer and autumn, using the same sampling size for each date as in 2011. Data collected in 2013 were analyzed with the model Ln (y) = β₀ + β₁X + β₂X². A comparison of regression coefficients was carried out between the 2011 and 2013 models with t (180+144-9-11-2=302, p<0.05) = 1.967. The results indicated that it is possible to use the 2011 regression model to estimate herbaceous aerial biomass from vegetation cover measurements with aerial photographs in La Cieneguilla site during summer and fall.     

A dynamic and stationary rheological study of erythrocytes incubated in a glucose medium

A higher than normal glucose concentration in a suspending medium may produce non-enzymatic glycosylation of erythrocyte proteins. This process can modify the viscoelastic properties of erythrocytes. In this paper, we studied the possible relationship between glucose concentration in a suspending medium and erythrocyte rheological parameters. Human venous blood was obtained from the antecubital veins of 10 healthy volunteers. Blood samples were anticoagulated with EDTA and centrifuged. Red blood cells (RBCs) were washed and subsequently divided in aliquots, which were incubated in vitro with glucose solutions of different concentrations. Dynamic and stationary viscoelastic parameters of RBCs were determined by laser diffractometry in an Erythrodeformeter. Aggregate shape parameter (ASP) of the RBCs was determined by digital image processing. Significant changes were observed both in ASP and in rheological parameters when the glucose concentration in the medium was increased, demonstrating that a glucose concentration as low as 1% induces alterations in the mechanical properties of RBCs.     

Digital automated RSA compared to manually operated RSA

The accuracy of digital Roentgen stereophotogrammetric analysis (RSA) was compared to the accuracy of a manually operated RSA system. For this purpose, we used radiographs of a phantom and radiographs of patients. The radiographs of the patients consisted of double examinations of 12 patients that had a tibial osteotomy and of double examinations of 12 patients that received a total hip prosthesis. First, the radiographs were measured manually with an accurate measurement table. Subsequently, the images were digitized by a film scanner at 150 DPI and 300 DPI resolutions and analyzed with the RSA-CMS software. In the phantom experiment, the manually operated system produced significantly better results than the digital system, although the maximum difference between the median values of the manually operated system and the digital system was as low as 0.013 mm for translations and 0.033° for rotations. In the radiographs of the patients, the manually operated system and the digital system produced equally accurate results: no significant differences in translations and rotations were found. We conclude that digital RSA is an accurate, fast, and user friendly alternative for manually operated RSA. Currently, digital RSA systems are being used in a growing number of clinical RSA-studies.