The Ca(2+)-transport system of yeast (Endomyces magnusii) mitochondria: independent pathways for Ca(2+) uptake and release.

Some features of the Ca(2+)-transport system in mitochondria of the yeast Endomyces magnusii are considered. The Ca(2+) uniporter was shown to be specifically activated by low concentrations of physiological modulators such as ADP, NADH, spermine, and Ca(2+) itself. The Na(+)-independent system responsible for Ca(2+) release from Ca(2+)-preloaded yeast mitochondria was characterized. The rate of the Ca(2+) release was proportional to the Ca(2+) load, insensitive to cyclosporin A and to Na(+), inhibited by La(3+), TPP(+), P(i), and nigericin, while being activated by spermine. We conclude that Ca(2+) release from preloaded E. magnusii yeast mitochondria is mediated by a Na(+)-independent pathway, very similar to that in mitochondria from nonexcitable mammalian tissues. A scheme describing an arrangement of the Ca(2+) transport system of yeast mitochondria is proposed.