Polyamines inhibit the ATP-dependent proteolytic pathway in rabbit reticulocyte lysates

Reticulocytes contain a soluble nonlysosomal proteolytic pathway that requires ATP and ubiquitin. Polyamines at physiological concentrations were found to inhibit rapidly the ATP-dependent proteolytic system in reticulocyte lysates; spermidine and putrescine inhibited this process by 26-72% and spermine by 71-96%. Spermine had little effect on the ATP-independent breakdown of oxidant-treated hemoglobin. By fractionating the ATP-dependent system, we show that polyamines inhibit the ATP-dependent degradation of ubiquitin-protein conjugates.