Vol. 47, No. 6, 1972 BIOCHEMICAL AND BIOPHYSICAL RESEARCH COMMUNICATIONS MEMBRANE PHASE ‘.tiNS’TIONS AS A DIAGNOSTIC TOOL FOR STUDYING MITOCHONDRIOGENES’S P. J. Ainsworth and E. Reno Tustanoff’ Department of Pathological Chemistry, University of Western Ontario, London, Canada and A. J. S. Ball Biology Department, Brock University, St. Catharines, Canada Received April 28, 1972 Summary: Utilizing an Arrhenius plot of membrane-bound enzyme activity, transition points were found which are characteristic of the major fatty acid found in the mitochondrial membrane. Cytochrome c oxidase was used as a marker enzyme to monitor the biogenesis of mitochondrial function on oxygen challenge in a wild type of Saccharomyces cerevisiae. It was found using Arrhenius kinetics, that the initially synthesized enzyme activity after exposure to oxygen was associated with anaerobically formed membranes (pro-mitochondria ?I and that subsequent activity was found to be laid down with new aerobically formed membranes. INTRODUCTION The most recent thesis for mitochondrial biogenesis is that which postulates the conversion of pro-mitochondria into mitochondria (I). In contrast to de y1ovo synthesis, this proposal implies the integration of new proteins (enzymes) into previously synthesized organelles. Various investigators (2,3,4) have shown that the lipid com- ’ This work was supported by the Medical Research Council of Canada through a grant in aid (MT 1460) to E.R.T. All correspondence dealing with this paper should be directed to this author. 1299 Copyright @ 1972, by Academic Press, Inc.