Some studies of the association of amino acid-activating enzymes with isolated microsomes of chick embryo

Abstract

The association of thirteen amino acid-activating enzymes with microsomal preparations from homogenated chick embryo has been studied by using the amino acid-dependent, adenosine triphosphate-inorganic pyrophosphate-P 32 (ATP-P 32P i 32) exchange assay. It was found that a substantial portion of the total activity of the amino acid-activating enzymes is associated with the microsomal fraction under the conditions employed. Extensive washing of the microsomes releases a portion of the activity of some of the amino acid-activating enzymes tested, but over 90% of the activity of the phenylalanine- and tyrosine-activating enzymes remains associated with the microsomes after four washes. Over 80% of the microsome-bound proline activation activity is destroyed by extensive washing, but if proline is present in the wash medium, over 70% of the proline activation activity remains associated with the microsomal fraction. The effects of treatment of the microsomes with sodium deoxycholate were studied, and this compound was found to completely inactivate most of the amino acid-activating enzymes. The lysine-, arginine-, and threonine-activating enzymes are largely unaffected by sodium deoxycholate treatment, and most of the activity of these enzymes is released from the microsomes into the soluble fraction.