AN IN-VITRO MODEL OF AGING - THE INFLUENCE OF INCREASING PHYSICAL DENSITY ON ENZYME-ACTIVITIES OF TRYPSIN, XANTHINE-OXIDASE AND SUPEROXIDE-DISMUTASE

The enzyme activities of trypsin (using an artificial substrate, N alp ha-benzoyl-L-arginine-ethylester BAEE), xanthine oxidase (XOD) and sup eroxide dismutase (SOD) were measured in the absence and presence of v arious concentrations of the following inert, water-soluble polymer vi scogens: polyvinylpyrrolidone (PVP-40), polyethyleneglycol (PEG-6000) and bovine serum albumin (BSA). Enzyme activities measured in the abse nce of viscogens were taken as 100%. In the presence of the viscogens, enzyme activities decreased considerably as follows: (i) Trypsin: to 2 or 12% in reaction mixtures containing 64 mg/ml PVP-40 or 481 mg/ml PEG-6000, respectively. (ii) XOD: to 29.3% in a reaction mixture conta ining 116 mg/ml PVP-40, to 68.9% in a medium containing 266 mg/ml PEG- 6000, and 38.1% in the presence of 138 mg/ml BSA. (iii) SOD: to 40.0, 19.9 and 16.6% in the same media as listed for XOD, respectively. The observations are consistent with the predictions of the molecular enzy me kinetic model (MEKM), and are also of importance for the membrane h ypothesis of aging, since the latter explains the loss of cell functio ns by an age-dependent increase of intracellular density which may cau se serious enzyme inhibitions.