Inhibition of electron transport activities in mitochondria from avocado and pepper fruit by naturally occurring polyamines

Abstract

The effects of the naturally occurring polyamines, spermine, putrescine, and spermidine were explored on mitochondrial state 3. state 4, and uncoupled respiration activities, ADP/O ratio, respiratory control ratio of pepper (Capsicum annuum L. cv. Early Cal Wonder) and avocado (Persea americana Mill. cv. Booth‐8 or Simmonds) mitochondria oxidizing either succinate, external NADH, malate, α‐ketoglutarate or tetramethyl‐p‐phenylenediamine. Abnormally high concentrations of spermine and spermidine such as might occur during chilling stress of these chilling‐sensitive fruits were detrimental to several oxidase activities, especially to external NADH oxidase. State 3 respiration for NADH oxidase was inhibited more than 70% by 10 mM spermine. The spermine inhibition of uncoupled NADH oxidase was not reversed by the presence of divalent cations including Ca2+, Mg2+, Mn2+, and Sr2+ at concentrations up to 10 mM or by 100 mM KCl. The inhibition primarily affected the Vmax. Other possible sites of polyamine interactions are discussed.