CYTOCHROME-C-OXIDASE IN NEUROSPORA-CRASSA CONTAINS MYRISTIC ACID COVALENTLY-LINKED TO SUBUNIT-1

Radiolabel from [H-3]myristic acid was incorporated by Neurospora cras sa into the core catalytic subunit 1 of cytochrome c oxidase (EC 1.9.3 .1), as indicated by immunoprecipitation. This modification of the sub unit, which was specific for myristic acid, represents an uncommon typ e of myristoylation through an amide linkage at an internal lysine, ra ther than an N-terminal glycine. The [H-3]myristate, which was chemica lly recovered from the radiolabeled subunit peptide, modified an invar iant Lys-324, based upon analyses of proteolysis products. This myrist oylated lysine is found within one of the predicted transmembrane heli ces of subunit I and could contribute to the environment of the active site of the enzyme. The myristate was identified by mass spectrometry as a component of mature subunit 1 of a catalytically active, purifie d enzyme. To our knowledge, fatty acylation of a mitochondrially synth esized inner-membrane protein has not been reported previously.