Interactions among cytochromes P-450 in the endoplasmic reticulum. Detection of chemically cross-linked complexes with monoclonal antibodies

The quaternary structure of rat liver cytochrome P-450 within microsomal membranes from 3-methyl-cholanthrene-treated rats was examined by a novel chemical cross-linking-monoclonal antibody approach. Complex formation among the different forms of P-450 was probed by cross-linking of membrane proteins followed by immunopurification with a monoclonal antibody (mAb) to P-450c, the major 3-methylcholanthrene-inducible form. Subsequent immunoblot analysis of the immunopurified proteins with this mAb indicated that P-450c formed complexes with other microsomal proteins. Immunoblots with mAbs to different P-450s were carried out to identify the P-450s that were cross-linked to P-450c. This approach detected specific cross-linking of P-450c to P-450 2a. Immunoinhibition experiments suggest that P-450 2a further metabolizes the primary phenols produced by P-450c-catalyzed hydroxylation of benzo[a]pyrene. Complex formation among membrane-bound enzymes has implications for their catalytic efficiency and an approach combining cross-linking and monoclonal antibody-based characterization of cross-linked proteins will be useful for elucidating such membrane protein macrostructures.     

Penetration of soil aggregates of finite size

Summary Maximum penetrometer pressure was measured on artificial soil aggregates of finite size (2–29 mm) using blunt probes (total cone angle 60°) driven at 3 mm min⁻¹. Maximum penetrometer pressure increased asymptotically with increase in dimensionless aggregate radius,b/a, wherea andb are the probe and aggregate radii, respectively. A theory was developed for penetration of blunt probes into soil aggregates of finite size. The theory assumed that plastic failure occurs out to a radius,R, and that beyond this only elastic straining occurs. This theory can be applied to estimate the radial and tangential stresses adjacent to a blunt probe. The estimated radial and tangential stresses increased with increase in dimensionless aggregate radius,b/a. The radius of the plastic front,R, around the probe is predicted to increase with increased aggregate size. The results also demonstrate the effect of soil shear cohesion and internal friction angle onR. The results are discussed with reference to root penetration.     

Inhibition of vitamin B12-dependent microbial growth by nitrous oxide

In methionine-free media, nitrous oxide inhibits the growth of an auxotrophic strain of Escherichia coli lacking a cobalamin-independent pathway for the de novo synthesis of methionine. Prototrophic E. coli is similarly inhibited by nitrous oxide if the cobalamin-independent pathway is selectively depressed by sulfanilamide. Nitrous oxide thus effectively inactivates cobalamin-dependent 5-methyltetrahydrofolate--homocysteine methyltransferase (methionine synthase, EC 2.1.1.13) in intact bacteria.     

Evaluation of the suchey–brooks method of age estimation in an Australian subpopulation using computed tomography of the pubic symphyseal surface

Despite the prominent use of the Suchey–Brooks (S–B) method of age estimation in forensic anthropological practice, it is subject to intrinsic limitations, with reports of differential interpopulation error rates between geographical locations. This study assessed the accuracy of the S–B method to a contemporary adult population in Queensland, Australia and provides robust age parameters calibrated for our population. Three‐dimensional surface reconstructions were generated from computed tomography scans of the pubic symphysis of male and female Caucasian individuals aged 15–70 years (n = 195) in Amira® and Rapidform®. Error was analyzed on the basis of bias, inaccuracy and percentage correct classification for left and right symphyseal surfaces. Application of transition analysis and Chi‐square statistics demonstrated 63.9 and 69.7% correct age classification associated with the left symphyseal surface of Australian males and females, respectively, using the S–B method. Using Bayesian statistics, probability density distributions for each S–B phase were calculated, providing refined age parameters for our population. Mean inaccuracies of 6.77 (±2.76) and 8.28 (±4.41) years were reported for the left surfaces of males and females, respectively; with positive biases for younger individuals (<55 years) and negative biases in older individuals. Significant sexual dimorphism in the application of the S–B method was observed; and asymmetry in phase classification of the pubic symphysis was a frequent phenomenon. These results recommend that the S–B method should be applied with caution in medico‐legal death investigations of Queensland skeletal remains and warrant further investigation of reliable age estimation techniques. Am J Phys Anthropol, 2013. © 2013 Wiley Periodicals, Inc.