Reactions of [14C]-3,4-Dichloroisocoumarin with Subunits of Pituitary and Spleen Multicatalytic Proteinase Complexes (Proteasomes)
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- 作者：Marian Orlowski ; Christopher Cardozo ; Anna Maria Eleuteri ; Ronald Kohanski ; Chih-Min Kam ; and James C. Powers
- 刊名：Biochemistry
- 出版年：1997
- 出版时间：November 11, 1997
- 年：1997
- 卷：36
- 期：45
- 页码：13946 - 13953
- 全文大小：188K
- 年卷期：v.36,no.45(November 11, 1997)
- ISSN：1520-4995
文摘
Exposure to [14C]-3,4-dichloroisocoumarin(DCI) of multicatalytic proteinase complexes (MPC)isolated from bovine pituitary and spleen leads to label incorporationinto several 
-type subunits, torapid inactivation of the chymotrypsin-like (ChT-L) activity, and to aslower inactivation of other activitiesof the MPC. The pituitary and spleen MPCs differ in that the firstcontains almost exclusively the X, Y,and Z subunits, whereas in the latter these subunits are largelyreplaced by LMP2, LMP7, and MECL1.Preincubation with two peptidyl aledhyde inhibitors of the ChT-Lactivity protected the X subunit in thepituitary MPC and unexpectedly the LMP2 subunit in the spleen MPC fromlabel incorporation, despitethe greater amino acid sequence homology of the LMP7 subunit to that ofthe X subunit. Losses in theyield of amino acids in both subunits, shown by amino acid sequencing,and lability of the DCI-proteinbond indicated formation of an acyl derivative by reaction of DCI withthe threonine OH group. Briefexposure to [14C]-DCI led to preferential incorporationof label into the LMP2 and X subunits, consistentwith the high inactivation rate constants of the ChT-L activity.Z-LLF-CHO, an inhibitor of ChT-L activity,but not Z-GPFL-CHO, an inhibitor of the branched chain amino acidpreferring component, preventedincorporation of radioactivity into the X subunits, whereas bothinhibitors prevented label incorporationinto LMP2, indicating differences in susceptibility to inhibitionbetween the two components. These andother data are consistent with involvement of the X and LMP2 subunitsin expression of the ChT-Lactivity in the pituitary and spleen MPC, respectively, and suggest thecatalytic functions of two other-subunits.
-type subunits, torapid inactivation of the chymotrypsin-like (ChT-L) activity, and to aslower inactivation of other activitiesof the MPC. The pituitary and spleen MPCs differ in that the firstcontains almost exclusively the X, Y,and Z subunits, whereas in the latter these subunits are largelyreplaced by LMP2, LMP7, and MECL1.Preincubation with two peptidyl aledhyde inhibitors of the ChT-Lactivity protected the X subunit in thepituitary MPC and unexpectedly the LMP2 subunit in the spleen MPC fromlabel incorporation, despitethe greater amino acid sequence homology of the LMP7 subunit to that ofthe X subunit. Losses in theyield of amino acids in both subunits, shown by amino acid sequencing,and lability of the DCI-proteinbond indicated formation of an acyl derivative by reaction of DCI withthe threonine OH group. Briefexposure to [14C]-DCI led to preferential incorporationof label into the LMP2 and X subunits, consistentwith the high inactivation rate constants of the ChT-L activity.Z-LLF-CHO, an inhibitor of ChT-L activity,but not Z-GPFL-CHO, an inhibitor of the branched chain amino acidpreferring component, preventedincorporation of radioactivity into the X subunits, whereas bothinhibitors prevented label incorporationinto LMP2, indicating differences in susceptibility to inhibitionbetween the two components. These andother data are consistent with involvement of the X and LMP2 subunitsin expression of the ChT-Lactivity in the pituitary and spleen MPC, respectively, and suggest thecatalytic functions of two other-subunits.