Question4 Complete the following sentence by selecting the most correct answer option from the list below. For the experiment on the formation of lactate by muscle extracts, the amount of lactate formed is ultimately quantified by: Select one alternative: the ionisation of the -OH group on lactate at a pH of 9.3 the reduction of pyruvate to lactate by lactate dehydrogenase the conversion of NADH to NAD+ the absorbance of lactate at 340 nm the oxidation of lactate to pyruvate by lactate dehydrogenase ResetMaximum marks: 1 Flag question undefined单项选择题
A
the ionisation of the -OH group on lactate at a pH of 9.3
B
the reduction of pyruvate to lactate by lactate dehydrogenase
C
the conversion of NADH to NAD+
D
the absorbance of lactate at 340 nm
E
the oxidation of lactate to pyruvate by lactate dehydrogenase

Question

Question4 Complete the following sentence by selecting the most correct answer option from the list below. For the experiment on the formation of lactate by muscle extracts, the amount of lactate formed is ultimately quantified by: Select one alternative: the ionisation of the -OH group on lactate at a pH of 9.3 the reduction of pyruvate to lactate by lactate dehydrogenase the conversion of NADH to NAD+ the absorbance of lactate at 340 nm the oxidation of lactate to pyruvate by lactate dehydrogenase ResetMaximum marks: 1 Flag question undefined单项选择题

A

the ionisation of the -OH group on lactate at a pH of 9.3

B

the reduction of pyruvate to lactate by lactate dehydrogenase

C

the conversion of NADH to NAD+

D

the absorbance of lactate at 340 nm

E

the oxidation of lactate to pyruvate by lactate dehydrogenase

BlackTom AI · Accepted Answer

Question4 Complete the following sentence by selecting the most correct answer option from the list below. For the experiment on the formation of lactate by muscle extracts, the amount of lactate formed is ultimately quantified by: Select one alternative: the ionisation of the -OH group on lactate at a pH of 9.3; the reduction of pyruvate to lactate by lactate dehydrogenase; the conversion of NADH to NAD+; the absorbance of lactate at 340 nm; the oxidation of lactate to pyruvate by lactate dehydrogenase.

Option 1: 'the ionisation of the -OH group on lactate at a pH of 9.3' This option focuses on a chemical deprotonation event, but the quantitative readout of such enzymatic formation assays is typically not governed by pH-driven ionisation of lactate itself. In most lactate formation assays, pH can influence reaction rates, but it is not the direct quantitative reporter of product formation itself. Thus this choice does not provide the mechanism by which the amount of lactate is measured.

Option 2: 'the reduction of pyruvate to lactate by lactate dehydrogenase' This describes the reverse reaction that converts pyruvate to lactate, which is catalyzed by lactate dehydrogenase under reducing conditions. In the context of forming lactate from muscle extracts, this backward reaction does not typically serve as the quantifiable readout of produced lactate unless the experimental setup is specifically designed to monitor reverse flux, which is uncommon for standard lactate assays.

Option 3: 'the conversion of NADH to NAD+' This option relates to the coupled enzymatic assay where lactate formation is linked to the oxidation of NADH to NAD+. The amount of NADH oxidized is stoichiometrically related to lactate produced, and this conversion provides the primary biochemical signal that is monitored to quantify lactate formation. In many standard assays, the decrease in NADH (absorbance at 340 nm) correlates with product formation, making this a plausible quantitative readout.

Option 4: 'the absorbance of lactate at 340 nm' Lactate itself does not have a significant absorbance at 340 nm in typical assay conditions. Instead, the useful signal at 340 nm arises from NADH, not from lactate directly. Therefore, this option misidentifies the actual chromophore responsible for the readout.

Option 5: 'the oxidation of lactate to pyruvate by lactate dehydrogenase' This describes the reverse reaction where lactate is converted back to pyruvate, which would not be the intended direction for quantifying lactate formation from muscle extracts. While lactate dehydrogenase can catalyze this reaction, standard assays quantify the forward formation of lactate via NADH oxidation, not the reverse oxidation of lactate itself.

The core idea in these types of assays is to couple lactate production to a detectable change in a reporter cofactor, typically NADH/NAD+. The most informative readout is the oxidation of NADH to NAD+, which reflects the amount of lactate produced. The other options either describe non-quantitative aspects (pH ionisation of lactate), refer to reverse reactions that do not serve as the primary readout, or incorrectly assign absorbance to lactate itself rather than to NADH.