Acta Biologica 42. (1991)

1-3. szám - A. Azaryan–G. Dovanjyan–A. Lajtha: Stress-induced change in cerebral ATP+ubiquitin-dependent proteinase activity vary with age

298 A. AZARYAN et al. elucidated. Although high levels of Ub have been detected in paired helical filaments that form neurofibrillary tangles in Alzheimer's disease /13/ pointing to a possible role of ATP+Ub-dependent proteolysis in the patho­genesis of senile degenerative processes, no reports are available on age­­related changes of cerebral UCDEN activity. Constitutive expression of Ub in brain is significant /10/ thus, the role of this evolutionally extremely conserved 76-amino-acid protein in the regulation of stress response may be of particular importance. UCDEN activity has been determined in rat brain at different ages and in immobilization stress conditions. Materials and Methods 3-7-month-old male rats have been used. Stress conditions have been produced by keeping 3- and 7-month-old animals in the cages with tied limbs at room temperature without feeding for 6 or 24 h. Rats were killed by de­capitation and the brain was removed. The whole brain tissue was homogen­ized in 5 volume of 20 mM Tris-HCl buffer, pH 7.6, containing 20 mM NaCl, 0.5 mM dithiothreitol, 0.1 mM EDTA, 1 mM MgCl„, and 20% glycerol at 4°C. 23,000 g supernatant was prepared and assayed ior UCDEN activity with 1% azocasein, 5mMQMg+22ATP and 4/uM Uo at pH 8.0 /2/. The incubation time was 2 h at 37 C. Enzyme activity was expressed as E366/min/mg protein. Results Cerebral UCDEN activity was 5% lower in 7-month-old rats than in 3-month-old ones (Table 1). This slight decrease proved to be a non-sig­nificant change. The protein content of the 3-month-old brain (9.1%) de­creased поп-essentially to 8.75% in the 7-month-old rats. Following 6h-long immobilization values of UCDEN activity have increased by 20% and 10% in 3- and 7-month-old animals respectively (Table 1). After 24h-long immo­bilization UCDEN activity decreased by 16% in 3-month-old rats; for 7- month-old animals these conditions turned to be mostly lethal.

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