Multiple Forms of Ubiquitin-Protein Ligase. Binding of Activated Ubiquitin to Protein Substrates

Pauline L. Lee, Christian F. Midelfort, Koko Murakami, Victor B. Hatcher

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Abstract

Enzyme activities that catalyzed the covalent attachment of ubiquitin to protein substrates (ubiquitin-protein ligase, UbL) were purified from the extracts of human red blood cells. These activities required the presence of ubiquitin-activating enzyme and ATP for activity. Four fractions (UbL A, B1B2, and C) were resolved and showed different specificities toward added substrates [carboxymethylated bovine serum albumin (CM-BSA), G-actin, lysozyme, and α-lactalbumin]. The enzyme fractions gave different products with a given substrate. UbL A and UbL B1 were exclusively active with CM-BSA and a-lactalbumin, respectively. UbL B2 was most active toward CM-BSA with substantial activities to G-actin and a-lactalbumin and with no activity to lysozyme. UbL C showed significant activities with all four substrates, having a highest activity toward CM-BSA. There were many endogenous proteins present in the erythrocyte extract which were efficient substrates for ubiquitin conjugation. In particular, a pair of substrates were identified from eythrocyte extracts which were far more efficient substrates than the denatured proteins exogenously added.

Original languageEnglish (US)
Pages (from-to)3134-3138
Number of pages5
JournalBiochemistry
Volume25
Issue number11
DOIs
Publication statusPublished - Jun 1986

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ASJC Scopus subject areas

  • Biochemistry

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