In the Walker/Karmen method for AST determination, which substrate is used by the enzyme (MDH)?

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Multiple Choice

In the Walker/Karmen method for AST determination, which substrate is used by the enzyme (MDH)?

Explanation:
In this coupled AST assay, the malate dehydrogenase step uses oxaloacetate as the substrate. AST converts aspartate and alpha-ketoglutarate to oxaloacetate and glutamate, then MDH reduces that oxaloacetate to malate while oxidizing NADH to NAD+. The assay tracks NADH consumption at 340 nm, so more AST activity drives more oxaloacetate formation and faster NADH loss. The other compounds aren’t substrates for MDH in this setup: malate is the product, and pyruvate or alpha-ketoglutarate aren’t used by MDH here.

In this coupled AST assay, the malate dehydrogenase step uses oxaloacetate as the substrate. AST converts aspartate and alpha-ketoglutarate to oxaloacetate and glutamate, then MDH reduces that oxaloacetate to malate while oxidizing NADH to NAD+. The assay tracks NADH consumption at 340 nm, so more AST activity drives more oxaloacetate formation and faster NADH loss. The other compounds aren’t substrates for MDH in this setup: malate is the product, and pyruvate or alpha-ketoglutarate aren’t used by MDH here.

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