Study of the surface secretion of the bronchiole using radioautography

The purpose of the present study was to obtain further information regarding the chemical nature and cell of origin of the surface secretion of the bronchiole using radioautography after the injection of labeled leucine, glucosamine, galactose. Rat lungs were perfused with mammalian Ringer's solution with added albumin. A 10-min pulse of L-leucine labeled with hydrogen-3 was administered, followed by perfusion with nonradioactive solution for 15 min to 4 hours. Similar studies were performed with [3H] glucosamine and [3H] galactose. Heavy labeling of the Clara cells of bronchioles was obtained after injection of [3H] L-leucine. Labeling of alveolar wall cells was also obtained. Labeling of the surface of the bronchiole was much heavier than the labeling of the surface of the alveoli. No specific labeling of bronchiolar cells was obtained with [3H] glucosamine and [3H] galactose. The results provide added evidence for the protein nature of the surface layer of the bronchiole and for the Clara cell as its cell of origin.     

Observations on the relationship of parathyroid hormone and calcitonin to plasma and liver phosphate

1. The action of two active forms of bovine trypsin (alpha and beta-trypsin) on a series of specific methyl ester substrates of general formula: N-acetyl-(glycyl)n-L-lysine methyl ester (n = 0, 1, 2) and N2-benzoyl-L-arginine ethyl ester have been investigated. With the L-lysine methyl esters the catalytic rate constant for hydrolysis (kcat) was found to be significantly lower for alpha-trypsin than for beta-trypsin, whereas with N2-benzoyl-L-arginine ethyl ester there was no significant difference for the two enzymes. 2. By measurement of the kinetic constants (kcat and Km) in the presence of a nucleophile, which competes with water in the deacylation process, it has been shown that, in common with the specific ester substrates of trypsin, the rate-determining step for the extended L-lysine methyl esters is decaylation of the enzyme. 3. It has been found that by extending the aminoacyl group of N-acetyl-L-lysine methyl ester by one glycine residue (n = 1), a greatly enhanced deacylation rate constant is observed for both alpha and beta-trypsin. The higher rate constants were maintained at the higher levels by the addition of a further glycine residue (n = 2). These results have been interpreted in terms of the 'induced fit' hypothesis the substrates binding to an enzyme subsite adjacent to the active site. 4. The beta-trypsin-catalysed hydrolysis of the L-lysine substrates was investigated over a range of temperature (15--35 degrees C). The Arrhenius law was obeyed, within experimental error, by all three substrates allowing the estimation of the thermodynamic function of activation (delta S not equal to and deltaH note equal to) for the deacylation reactions. The significantly higher values of deltaS not equal to and deltaH not equal to obtained for the two extended substrates are interpreted in terms of additional hydrogen bonding between the longer aminoacyl chains and the enzyme molecule. The results are compared with those for non-extended specific substrates, which have a possible hydrophobic interaction with the enzyme surface.     

Wear of a Fe2.5Ni2.5CrAl Multiprincipal Element Alloy: A Combined Experimental and Molecular Dynamics Study

The Fe2.5Ni2.5CrAl multiprincipal element alloy (MPEA) is a promising material for engineering applications because of its high strength and plasticity values. To evaluate the friction and wear performance, reciprocating dry sliding tests and molecular dynamics (MD) simulations are performed to determine the wear mechanism over a range of length scales. This alloy exhibits a lower average friction coefficient and wear volume loss during dry sliding compared with the well-known Fe2Ni2CrAl alloy. The worn surface morphology reveals abrasive scratches, grooves, and delamination. The fine wear debris possesses high oxygen content, leading to higher wear resistance. The wear mechanism involves abrasive, adhesive, and oxidative wear. The wear, atomic stress and shear strain, dislocations, and lattice structure are analyzed by MD simulations. Point defects, atomic clusters, and stacking faults are identified in the nanowear process. The behavior of the $1/6<112>$(Shockley)-type dislocations is identified as the main dislocation mechanism during sliding. Stacking faults produced during the stress release process are present in the indentation. This work provides a deep insight into the friction and wear behavior of Fe2.5Ni2.5CrAl MPEAs.