ALBERT

Notes: [Auszug] IN this book Professor Satterfield has squeezed into less than 400 pages the essential characteristics of catalysis and many of the major industrial catalytic processes. He has not attempted to be either up to date (there are few references later than 1976), or comprehensive in his coverage, but ...

Notes: [Auszug] Bovine brain calmodulin was purified essentially according to Watterson et al.8 with the exception that the acid-ammonium sulphate step was omitted. Methyl group (0.2 to 0.5 mol) was incorporated into calmodulin during 30 min at 37 C in the following incubation medium: 0.5 ?g calmodulin, 0.25 M ...

Notes: [Auszug] Plant Taxonomy and Biosystematics. By Clive A. Stace. Pp.279. (Edward Arnold/University Park Press: 1980.) Flexi 8.95, 29.50. PLANT taxonomy in the modern context is very much a multidisciplinary subject and encompasses various types of botanical investigations and techniques. According to the ...

Notes: Abstract Widely extended, cation stacking faults in experimentally deformed Mg2GeO4 spinel have been studied using transmission electron microscopy (TEM). The faults lie on {110} planes. The displacement vector is of the form $$\frac{1}{4}\left\langle {1\bar 10} \right\rangle $$ and is normal to the fault plane. The partial dislocations which bound the stacking fault have colinear Burgers vectors of the form $$\frac{1}{4}\left\langle {1\bar 10} \right\rangle $$ which are normal to the fault plane.

Notes: Abstract An outline is given of the existing nondestructive vibration tests for cast irons and their drawbacks in terms of the dimensional accuracy of the components. A proposal is made for a new test based on the change of resonant frequency with vibration amplitude exhibited by cast irons. This proposal is evaluated using material data obtained from dynamic tests of a wide range of cast iron specimens. A test rig is described suitable for testing cylindrical cast bars, and typical results are presented in relation to material strength. There is also a brief description of preliminary testing on cast products.

Notes: Summary Choleragen exerts its effects on cells through the activation of adenylate cyclase. The initial event appears to be the binding of the B subunit of the toxin to ganglioside GM1 on the cell surface, following which there is a delay prior to activation of adenylate cyclase. Patching and capping of the toxin on the cell surface, perhaps involved in the internalization of the enzymatically active subunit, may be occuring during this time. The activation of adenylate cyclase, which is catalyzed by the A1 peptide of choleragen, does not require the B subunit or ganglioside GM1. The A1 peptide catalyzes the transfer of ADP-ribose from NAD to an amino acid, probably arginine, in a 42 000 dalton membrane protein. This protein appears to be the GTP-binding component (or G/F factor) of the adenylate cyclase system and is cruical to the regulation of cyclase activity by hormones such as epinephrine. ADP-ribosylation of the G/F factor is enhanced by GTP and, in some systems, by a cytosolic factor. GTP is also required for stabilization and optimal catalytic function of the choleragen-activated cyclase. Calmodulin, a calcium-binding protein, is necessary for expression of catalytic activity of the toxin-activated adenylate cyclase in brain and other tissues. The ADP-ribosyltransferase activity required for activation of the cyclase is an intrinsic property of the A1 peptide of choleragen which is expressed only after the peptide is released from the holotoxin by reduction of a single disulfide bond. In the absence of cellular components, choleragen catalyzes the ADP-ribosylation of small guanidino compounds such as arginine as well as peptides and proteins that contain arginine. It is assumed, therefore, that the site of ADP-ribosylation in the natural acceptor protein is an arginine or similar amino acid. When guanidino compounds are not present as ADP-ribose acceptors, choleragen hydrolyzes NAD to ADP-ribose and nicotinamide at a considerably slower rate. E. coli heat-labile enterotoxin (LT) is very similar to choleragen in structure and function. It consists of two types of subunits, A and B, with sizes comparable to those of the A and B subunits of choleragen. Binding of LT to the cell surface is enhanced by prior incorporation of GM1 but not other gangliosides; the oligosaccharide of GM1 specifically interacts with LT and its B subunit. The A subunit of LT exhibits ADP-ribosyltransferase activity following activation by thiol to release the A1 peptide. The A subunit of LT can be isolated in an ‘unnicked’ form and thus requires, in addition to reduction by a thiol, proteolytic cleavage to generate the active A1 peptide. Like choleragen, LT uses guanidino compounds as model ADP-ribose acceptors and catalyzes the ADP-ribosylation of a 42 000 dalton protein in cell membrane prepatations. ADP-ribosyltransferases that use arginine as ADP-ribose acceptors are not restricted to bacterial systems; such an enzyme has been purified to apparent homogeneity (〉500 000-fold) from turkey erythrocytes. Based on a subunit molecular weight of 28 000, its turnover number with arginine as the ADP-ribose acceptor is considerably higher than that of either toxin. Although with low molecular weight guanidino derivatives the substrate specificity of the enzyme is similar to that of choleragen, with protein substrates it clearly differs. The physiological role of the turkey erythrocyte transferase remains to be established.

Notes: Abstract Quantitative molecular orbital (MO) calculations and qualitative perturbational MO arguments are used to interpret the spectra and structure of transition metal dichalcogenides and related compounds. Competition between pyrite (FeS2), marcasite (FeS2) and loellingite (FeAs2) structure types is explained in terms of the number of electrons occupying a set of MO's obtained from the mixing of dianion (A 2) orbitals and metal (M) dσ orbitals. Direct metal-metal d orbital interaction is argued to be small. Attention is focused upon the M - A - M angles which differ substantially among the three structure types as a consequence of varying numbers of electrons in orbitals which closely resemble the pπ* orbitals of the dianions. Variations in M - A and A - A distances can also be understood in terms of the occupations of this set of MO's. Disulfide valence region photo-emission spectra are interpreted in terms of calculations on MS6 and S6 molecular clusters. M3d orbitals are found to progressively approach the S3p orbitals with increasing atomic number of M from Fe to Ni. For CuS2 comparison of calculation and experiment supports an approximate electron configuration of Cu+1 S 2 −1 .