The NH2‐terminal residues of rat liver proteasome (multicatalytic proteinase complex) subunits, C2, C3 and C8, are Nα‐acetylated

Abstract
Rat liver proteasome (multicatalytic proteinase complex) is a 20S‐ring shaped particle having a molecular mass of 750 kDa, and iscomposed of at least 13 non‐identical components ranging from 21 to 31 kDa in size. We found here that the NH2‐terminal residues of all the known 13 components, except for C5, are not reactive to phenylisothiocyanate. Among them, components C2, C3 and C8 are blocked in their NH2‐termini with Nα‐acetyl‐Met, Nα‐acetyl‐Ala, and Nα‐acetyl‐Ser, respectively. The NH2‐terminal portions of C2, C3, and C8 exhibit sequence similarity to one another, but that of the non‐blocked component C5 differs from those of C2, C3, and C8.