TABLE 5.

Small-peptide- and protein-hydrolyzing activities of M. thermophila 20S proteasomes altered by amino acid replacements in the β_Δ subunit

Alterationb	Sp acta
	CL	PG	TL	Proteolysis
None	95 ± 0.83	106 ± 2.1	2.30 ± 0.38	54.0 ± 0.97
Thr1→Ala	UDc	UD	UD	UD
Thr2→Ala	40 ± 1.4	32 ± 2.8	0.48 ± 0.07	10.0 ± 0.40
Thr1→Ser	72 ± 3.4	24 ± 0.84	0.35 ± 0.02	9.1 ± 0.09
Asp51→Asn	204 ± 3.0	155 ± 0.75	2.30 ± 0.08	35.0 ± 1.4
Lys33→Ala	UD	UD	7.10 ± 0.36	1.7 ± 0.03
Lys33→Arg	27 ± 1.2	9 ± 0.08	0.30 ± 0.04	8.6 ± 0.68

^aCL activity was determined with 150 μM Suc-LLVY-Amc, PG activity was determined with 150 μM Cbz-LLE-βNa, and TL activity was determined with 300 μM Benz-FVR-Amc. CL, PG, and TL activities are expressed as nanomoles per minute per milligram. Proteolysis activity was determined with lysozyme and is expressed as nanomoles of leucine equivalents per minute per milligram of protein. The proteolysis assay contained 1.0 mg of substrate/ml and 0.17 mg of 20S proteasome/ml. All assays were done at 60°C. 

^bAmino acid replacements were in the β_Δ subunit of 20S proteasomes heterologously produced by coproduction of α and β_Δ subunits in E. coli. The β_Δ subunit has the propeptide deleted. 

^cUD, undetectable.