Cell types of the pars distalis of the hedgehog (Erinaceus europaeus L.) adenohypophysis: cytological, immunocytochemical and ultrastructural studies. 4. Thyrotropic cells

Staining and histochemical methods, immunofluorescence and electron microscopy were used to individualize the thyrotropic cells in the adenohypophysis of the non-hibernating hedgehog. One cell type was differentiated; its characteristics at the light and electron-microscopic levels were presented. Immunofluorescence has confirmed the functional significance of this cell type and the validity of the denomination of 'thyrotropic cells'.     

Crystal structure determination, refinement and the molecular model of the alpha-amylase inhibitor Hoe-467A

The crystal and molecular structure of the alpha-amylase inhibitor Hoe-467A has been determined and refined at high resolution. The polypeptide chain is folded in two triple-stranded sheets, which form a barrel. The topology of folding is as found in the immunoglobulin domains. The amino acid triplet Trp18-Arg19-Tyr20 has an exceptional conformation and position in the molecule and is possibly involved in inhibitory activity.     

Epiphyseal-based designs for tibial plateau components--II. Stress analysis in the sagittal plane

A two-dimensional, finite element study was undertaken to establish the stresses in the proximal tibia before and after total knee arthroplasty. Equivalent-thickness models in a sagittal plane were created for the natural, proximal tibia and for the proximal tibia with two different types of tibial plateau components. All components simulated bony ingrowth fixation, i.e. no cement layer existed between component and bone. In addition, the interface between component and bone was assumed to be intimately connected, representing complete bony ingrowth and a rigid state of fixation. Two load cases were considered: a joint reaction force acting in conjunction with a patellar ligament force, simulating the knee at 40 degrees of flexion; and a joint reaction force directed along the long axis of the tibia. For the natural tibia model, the pattern of principal stresses for loadcase 1 more closely corresponds to the epiphyseal plate geometry and trabecular morphology than do the principal stress patterns for loadcase 2. Judging from the distribution of principal stresses, loadcase 1 represents a more severe test of implant design than does loadcase 2. The model of the component with a peg predicted that the trabecular bone near the tip of the peg will experience higher than normal stresses, while the bone stresses near the posterior aspect adjacent to the metal tray will be reduced. A component without pegs that incorporates a posterior chamfer and an anterior lip lead to stress distributions closer to those existing in the natural tibia. The interface geometry for this design is based upon the contour of the epiphyseal plate.     

Isolation and structure elucidation of an alpha-amylase inhibitor, AI-3688, from Streptomyces aureofaciens

A novel polypeptide inhibitor, AI-3688, which acts upon human pancreatic alpha-amylase, was isolated from fermentation broth of Streptomyces aureofaciens. The purified peptide contains no unusual amino acids. Its Mr is 3936. The primary structure of AI-3688 was elucidated by automatic Edman degradation of the native or modified inhibitor. Two intramolecular cysteines form a disulphide bridge, thus creating a ring structure consisting of 17 amino acids. Strong sequence homology also exists to another microbial alpha-amylase inhibitor, tendamistat (HOE 467). This paper discusses the role of a common partial sequence, -Gln-Ser-Trp-Arg-Tyr-, present in the loop of both inhibitors as the active site of microbial peptide alpha-amylase inhibitors.     

Changes in the electrophoretic pattern of the venom of the bushmaster (Lachesis muta stenophrys) stored under various conditions

Liquid and lyophilized samples of Lachesis muta venom were stored at different temperatures and for different periods of time, and analyzed by polyacrylamide gel electrophoresis (PAGE) and immunoelectrophoresis. Only slight variations were evident when three pools of freeze-dried venom, that had been kept at -30 degrees C for several months were compared with fresh venom. These results suggest that L. muta venom is not altered drastically when stored under these conditions.     

Implementation of periodic acid-thiosemicarbazide-silver proteinate staining for ultrastructural assessment of muscle glycogen utilization during exercise

Summary Distribution of glycogen particles in semithin and ultrathin sections of biopsy samples from human muscles subjected to either short- or long-term running were investigated using PAS and Periodic Acid-ThioSemiCarbazide-Silver Proteinate (PA-TSC-SP) staining methods. Glycogen particles were predominantly found immediately under the sarcolemma or aligned along the myofibrillar Iband. After long-term exhaustive exercise type-1 fibers with a few or no glycogen particles in the core of the fibers were frequently observed. The subsarcolemmal glycogen stores of these depleted type-1 fibers were about three times as large as after exhaustive short-time exercise. Another indication of utilization of subsarcolemmal glycogen stores during anaerobic exercise was that many particles displayed a pale, rudimentary shape. This observation suggests fragmental metabolization of glycogen. Thus, depending on type of exercise and type of fiber differential and sequential glycogen utilization patterns can be observed.     

Protoplast forming ability in the genusBrevibacterium

Formation of protoplasts and their reversion were followed in 7 strains of brevibacteria. The formation of protoplasts and their reversion differed both between various species of brevibacteria and between various mutant strains of the same species.     

Inhibition of S-adenosyl-L-methionine sterol-C-24-methyltransferase by analogues of a carbocationic ion high-energy intermediate. Structure activity relationships for C-25 heteroatoms (N, As, S) substituted triterpenoid derivatives

Microsomes from maize seedlings are capable of catalyzing the C-24 alkylation of 4,4,14 alpha-trimethyl-9 beta,19-cyclo-5 alpha-cholest-24-en-3 beta-ol (cycloartenol) by (S)-adenosyl-L-methionine (AdoMet) leading to 24-methylene cycloartanol. Derivatives of cycloartenol bearing a nitrogen atom at C-25 have been previously shown to be potent inhibitors of the AdoMet-cycloartenol-C-24-methyltransferase (Narula, A. S., Rahier, A., Benveniste, P., and Schuber, F. (1981) J. Am. Chem. Soc. 103, 2408-2409). In order to determine the molecular parameters of the inhibition and to gain information about its mechanism, various azasteroids and analogues have been synthesized and assayed. The following results have been obtained. i) The presence of a positive charge at position 25 was found to be the major cause of the inhibition since electrostatically neutral isosteric compounds possessing a carbon in place of the nitrogen atom were not inhibitory. The positive charge leading to inhibition may be conferred by a protonated amine, a quaternary ammonium group, as well as by a sulfonium or an arsonium group. ii) A steroid-like structure of the inhibitor was also important. And iii) the presence of a free 3 beta-hydroxy group and the bent conformation of cycloartenol, which are essential molecular features of the substrate for the methylation reaction, were no longer required to observe inhibition. The data obtained strongly support the idea that C-25 heteroatoms (N, As, and S), substituted triterpenoid derivatives possessing a positive charge at position 25, are analogues of a carbocationic high-energy intermediate involved during the reaction catalyzed by the AdoMet-cycloartenol-C-24-methyltransferase.