Location of Enzymes in Mitochondria Fractions

Abstract

IT appears from several published works during recent years that a large number of enzymes have been located in the mitochondria fractions by means of differential centrifugation of tissue homogenates, especially of animal cells. Duve and Berthet¹ have tried to standardize the conditions of centrifugation in different types of instruments so that the results may be reproduced, and they urge that some attention should be paid to such factors as diffusion- and convection-currents and also to the manner of decantation. Some errors are, however, possible with this type of work, as have been pointed out by Brachet² while discussing the nuclear control of enzymic activities; during homogenization and differential centrifugation soluble enzymes can no doubt be adsorbed on particles; but the microsomes (submicroscopic cytoplasmic granules) may release enzymes which are normally bound to them just as in the case of crushing the cell constituents in different media. By this method it is scarcely possible to get information on the interactions occurring between the different fractions in a normal living cell and to be sure that the various particles obtained by differential centrifugation are really the ones which pre-existed in the intact cell. In this connexion, Holter³ has also discussed the profound changes that the process of homogenization involves; he points out that the hyaline ground plasm of most cells is not miscible with water and that a certain degree of autolysis is indispensable in order to set the cytoplasmic particles free and that this autolysis must have far-reaching consequences with regard to enzyme yield and enzyme distribution.