| 4321894 |
Holbrook JJ, Stinson RA: Reactivity of the essential thiol group of lactate dehydrogenase and substrate binding. Biochem J. 1970 Nov;120(2):289-97.
1. The preparation of a derivative of pig heart lactate dehydrogenase in which the essential thiol group has been converted into an S-sulpho group is described. The derivative has unchanged s (20,w) and is catalytically inactive. 2. The rate of reaction of the essential thiol group is controlled by a system with a pK> 9. 3. The essential thiol group is protected by NADH against reaction with maleimide. 4. Lactate dehydrogenase in which the essential thiol group has been converted into an S-sulpho group or alkylated with maleimide still binds one molecule of NADH/subunit but with a three- to four-fold diminished affinity. 5. The inhibited enzymes also bind one molecule of NAD (+)-sulphite complex/subunit but with affinity decreased 10 (3)-10 (4)-fold. 6. The inhibited enzymes fail to bind C (2) and C (3) molecules to give the ternary complexes enzyme-NAD (+)-pyruvate, enzyme-NADH-oxamate and enzyme-NADH-oxalate. The 1:1:1 stoicheiometry of the last-mentioned complex with the native enzyme was established by gel filtration. 7. Structures that account for these results are discussed. |
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