Study of thermal denaturation of lysozyme and other globular proteins by light-scattering spectroscopy

The technique of intensity correlation light-scattering spectroscopy has been used to accurately determine the extent of physical swelling of lysozyme, ribonuclease, and chymotrypsinogen produced by thermal denaturation. The change in hydrodynamic radius is deduced from direct measurements of the diffusion coefficient, carried out in the temperature range 20° to 70°C at various values of pH in the range 1.0 to 3.0 at ionic strengths of from 0.01 M to 0.2 M. An average radius increase of 18% is observed for lysozyme and ribonuclease, with an estimate of 26% for chymotrypsinogen. Analysis of the pH dependence of the transition temperature leads to the conclusion that the lysozyme charge increases by approximately +2e during unfolding. We have applied this value of the charge increase along with the 18% average radius increase to estimate the electrostatic contribution to the free-energy change for denaturation of lysozyme. The results are consistent with the experimental observation that the transition temperature is nearly independent of ionic strength.     

Pompholyx of the nail organ and the true onychomycosis

Pompholyx is one clinical form of the endoparasitic-hematogenous skin eruptions. It is characterized by sago-grain-like, deeply embedded blisters or pustules within the normal, primarily non-inflamed skin, localized to the palms, soles, fingers, toes and interdigital webs, and in the nail organ. The blisters may be located in the nail wall causing paronychia, and/or beneath the nail plate causing onychia. The discussion of the etiology and pathogenesis of the pompholyx of the nail organ is inseparable from pompholyx at other sites (e.g. palms and soles), since they are identical. Hence, the term pompholyx should replace such misleading terms as infectious eczematoid dermatitis, id eruption, of the hand and/or feet, dermato- or epidermophytosis, dyshidrosis, and the vernacular athlete's foot. Even though hyphomycetes (true pathogens and common molds) of many sorts may be detected in the roof of the blisters, particularly on the feet, and scrapings of detritus from the nails, they have no role in the etiology or pathogenesis of this condition. Due to an universal infection immunity pompholyx is not infectious or transmissible. True onychomycosis is clinically and pathogenetically an entirely different condition. The purpose of this paper is to clarify the fundamental differences in etiology and pathogenesis between the two conditions.     

Amyloid beta-protein fibrillogenesis. Structure and biological activity of protofibrillar intermediates.

Alzheimer's disease is characterized by extensive cerebral amyloid deposition. Amyloid deposits associated with damaged neuropil and blood vessels contain abundant fibrils formed by the amyloid beta-protein (Abeta). Fibrils, both in vitro and in vivo, are neurotoxic. For this reason, substantial effort has been expended to develop therapeutic approaches to control Abeta production and amyloidogenesis. Achievement of the latter goal is facilitated by a rigorous mechanistic understanding of the fibrillogenesis process. Recently, we discovered a novel intermediate in the pathway of Abeta fibril formation, the amyloid protofibril (Walsh, D. M., Lomakin, A., Benedek, G. B., Condron, M. M., and Teplow, D. B. (1997) J. Biol. Chem. 272, 22364-22372). We report here results of studies of the assembly, structure, and biological activity of these polymers. We find that protofibrils: 1) are in equilibrium with low molecular weight Abeta (monomeric or dimeric); 2) have a secondary structure characteristic of amyloid fibrils; 3) appear as beaded chains in rotary shadowed preparations examined electron microscopically; 4) give rise to mature amyloid-like fibrils; and 5) affect the normal metabolism of cultured neurons. The implications of these results for the development of therapies for Alzheimer's disease and for our understanding of fibril assembly are discussed.     

Effect of age on high-fat diet-induced hypertension

Aging and obesity both have a significant impact on central blood pressure (BP) regulation, and previous studies indicated that changes in central redox signaling with age may affect high-fat (HF) diet-induced cardiovascular responses. Therefore, we investigated the effects of 60% HF feeding on BP regulation in young adult (5 mo) and old (26 mo) Fischer-344 × Brown-Norway rats. Radiotelemetric transmitters were implanted to measure BP, heart rate (HR), locomotor activity, and spontaneous baroreflex sensitivity. Expression and activity of NADPH oxidase and ANG II type 1 receptor were assessed in the hypothalamus and in the nucleus tractus solitarii. Old animals gained more weight on HF diet compared with young, whereas central NADPH oxidase expression and activity elevated similarly in the two age groups. After an initial hypotensive and tachycardic response during the first week of HF feeding, BP in young animals increased and became significantly elevated after 6 wk of HF feeding. In contrast, BP in old animals remained depressed. Nighttime HR and locomotor activity decreased in both young and old rats fed with HF diet, but these changes were more significant in young rats. As a result, amplitudes of circadian variation of BP, HR, and activity that were originally higher in young rats declined significantly and became similar in the two age groups. In conclusion, our experiments led to the surprising finding that HF diet has a more serious impact on cardiovascular regulation in young animals compared with old.