Effects of Delipidation on Proton Translocation and ATPase Activity in Beef Heart Electron Transport Particles

Abstract

Delipidation of beef heart electron transport particles with phospholipase A₂ has been examined. When the particles were treated with the lipase and subjected to a low bovine serum albumin wash, ATPase activity was unaffected as was the lipid/protein ratio of the particles. However, energisation by ATP/Mg²⁺ was abolished. Furthermore, unsaturated but not saturated fatty acids discharged the steady-state ATP-driven membrane potential of control samples. When the phospholipase A₂ hydrolysis products were removed, inhibition of energy-linked reactions in the lipid-depleted particles was still observed and was interpreted in terms of non-specific leaks in the vesicle membranes, and ‘specific’ leaks through impaired H⁺-ATPase complexes. ATPase activity was less susceptible to delipidation than energisation but was, nevertheless, strongly inhibited at 50 percent lipid depletion.

Spin label studies indicated a decrease in the fluidity of particle membranes accompanying delipidation. Moreover, the discontinuity seen in Arrhenius plots of ATPase activity was shifted from 17°C (control) to 22°C at 50 percent phospholipid depletion. The data are consistent with a release of unsaturated fatty acids by phospholipase A₂ rendering the transport particles both leakier and the membranes less fluid than controls.

Key Words:

• Delipidation
• mitochondria
• proton translocation
• membrane potential
• phospholipid
• H⁺-ATPase
• phospholipase