![(DEC 2019) 37. Given below is the [P] vs time plot of an enzymatic reaction carried out by the enzyme X Which one of the following statements is the correct interpretation of the data? (1) The Km and Vmax of the enzyme X are 15 and 60 units, respectively. (2) The Vmax is 60 but the Km cannot be determined (3) The Km 15 but the Vmax cannot be determined (4) Neither the Km nor the Vmax of the enzyme X can be determined from these data](data:image/svg+xml;nitro-empty-id=MTE4NjoxMTY3-1;base64,PHN2ZyB2aWV3Qm94PSIwIDAgMTkyMCAxMDgwIiB3aWR0aD0iMTkyMCIgaGVpZ2h0PSIxMDgwIiB4bWxucz0iaHR0cDovL3d3dy53My5vcmcvMjAwMC9zdmciPjwvc3ZnPg==)
The correct answer is (2) The Vmax is 60 but the Km cannot be determined.
Introduction
Graphical data are fundamental tools in enzyme kinetics, helping derive quantitative parameters such as Vmax and Km. A typical plot of product concentration ([P]) versus time visualizes how quickly an enzyme generates product under specific conditions. The ability to interpret such plots and extract meaningful kinetic parameters is critical for experimental biochemistry, diagnostics, and academic evaluation. This article explains how to read [P] vs time plots, clarifies what information can and cannot be obtained, and solves a representative competitive exam question using these principles.
The [P] vs Time Plot: What Does It Show?
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Y-axis: Product concentration, [P]
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X-axis: Time (seconds)
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Enzyme reactions start with rapid product accumulation, which gradually plateaus as substrate depletes and/or product is inhibited.
Determining Vmax
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Vmax is the maximum initial rate at which product forms.
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On the [P] vs time plot, the steepest slope (initial linear portion) represents this maximum velocity.
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In the provided plot, product reaches 60 units, corresponding to the maximum rate displayed by the plateau.
Determining Km
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Km is the Michaelis constant, reflecting substrate affinity.
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Km requires measurement of reaction velocity across a range of substrate concentrations, not just the time-course of a single reaction.
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The [P] vs time plot alone, without varying substrate concentrations, does not allow for direct estimation of Km.
Why Km Cannot Be Determined
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Km is defined as the substrate concentration at which reaction velocity is half of Vmax (Vmax/2).
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Requires data from multiple substrate concentrations and a velocity–substrate concentration plot (Michaelis-Menten curve).
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With only [P] over time, Km remains undefined.
Stepwise Data Interpretation
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Vmax Determination:
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The horizontal asymptote in the [P] vs time plot reflects the point where maximum enzyme velocity is attained before substrate depletion or inhibition slows the reaction.
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The value where [P] plateaus (e.g., 60 units) can be interpreted as Vmax under the given conditions.
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Km Determination:
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Not possible from a single time-course plot—additional experimental data needed.
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Summary Table
| Plot Feature | Parameter Inferred | Can Be Determined? |
|---|---|---|
| Max. [P] plateau/steep slope | Vmax | Yes |
| [S] for half-max velocity | Km | No |
Conclusion
For a single [P] versus time plot from an enzyme reaction, Vmax (maximum velocity, here shown as 60 units) can be determined from the plateau, but Km cannot be determined without more data. Hence, the correct answer is:
The Vmax is 60 but the Km cannot be determined.
37 Comments
Varsha Tatla
September 13, 2025Here Vmax is 16 but km is not find because here instead of substrate concentration time give at x axis
Km =vax/2
Khushi Vaishnav
September 13, 2025The Vmax is 60 but the Km cannot be determined.
Aakansha sharma Sharma
September 13, 2025Here Vmax is 60 but km is not find because here instead of substrate concentration time give at x axis
Km =vax/2
Kajal
September 14, 2025Correct answer is 2
Here vmax is 60 and km is not determined..
Mohd juber Ali
September 14, 2025Vmax = 60
Km = half of maximum valocity. But we can not calculate km bcz x-axis = time not substrate
So km define at substarte concentration .not time
Pratibha Jain
September 14, 2025correct answer is option (2)
The Vmax is 60 but the Km cannot be determined.
Aafreen Khan
September 14, 2025Option 2 is correct answer
The Vmax is 60 but the Km cannot be determined.
Pooja
September 14, 2025The Vmax is 60 but the Km cannot be determined
Dharmpal Swami
September 14, 2025Vmax is 60 but km cannot be determined
Kanica Sunwalka
September 14, 2025V max is 60 but Km cannot be determined ( substrate conc is not known )
option 2 is correct
Soniya Shekhawat
September 14, 2025The Vmax is 60 but the Km cannot be determined bcz substrate concentration is not known , So option 2 is right.
Kirti Agarwal
September 14, 2025Vmax is 60 but km is not determine
Santosh Saini
September 14, 2025The Vmax is 60 but the km cannot be determined
Rishita
September 14, 2025The Vmax is 60 but the Km cannot be determined.
Khushi Agarwal
September 14, 2025Option b is correct answer
The Vmax is 60 bt the Km cannot be determined
Manisha choudhary
September 14, 2025Km substrate concentration p calculate ki jaati h jaha vmax kaa half ho km is substrate concentration at which vmax /2
Product verses time graph s km direct pta nhi kr skte
Vmax initial concentration jaha maximum catalysis hota
Sakshi Kanwar
September 14, 2025Vmax is 60 but Km is not determined because km is that substrate concentration where V is half of Vmax
Bhawna Choudhary
September 14, 2025The vmax is 60 but the km is not determined
Vanshika Sharma
September 14, 2025Vmax is 60 but the Km is not determined
Konika Naval
September 14, 2025The Vmax is 60 but the Km cannot be determined.
Tanvi Panwar
September 14, 2025Vmax. is 60 but the substrate conc. cannot be determined.
HIMANI FAUJDAR
September 14, 2025Ans Vmax can be determined which is 60 but km cannot be determined for a single [P] versus time plot from an enzyme reaction.
Muskan singodiya
September 14, 2025Vmax can be detrmine which is 60 but Km cannot be detrmine
Option 2
Nilofar Khan
September 15, 2025correct answer is (2)
The Vmax is 60 but the Km cannot be determined becouse instead of sub. Concentration time will be given at x-axis.
Payal Gaur
September 15, 20252. The Vmax is 60 but the km is not be determined because km is not depends on time( km is rate constant) and in the graph on x axis time is given
Mansukh Kapoor
September 15, 2025The correct answer is option 2nd
The Vmax is 60 but the Km cannot be determined
Ankita Pareek
September 15, 2025Vmax is 60 but km is not defined from the x axis because km is determined from substrate concentration and in the given graph time is given at the x axis
Pallavi Ghangas
September 15, 2025The Vmax is 60 but the Km cannot be determined.
Bhavana kankhedia
September 15, 2025The Vmax is 60 but the Km cannot be determined.
Anjana sharma
September 16, 2025Vmax= 60 km unidentified
Sonal nagar
September 16, 2025Option 2
The Vmax is 60 but the Km cannot be determined.
Avni
September 16, 2025The correct answer is (2) The Vmax is 60 but the Km cannot be determined.
Palak Sharma
September 16, 2025The Vmax is 60 but the Km cannot be determined.
Muskan Yadav
September 17, 2025The Vmax is 60 but the Km cannot be determined.
Minal Sethi
September 18, 2025Vmax is 60 but Km can not be determined
option 2
Deepika sheoran
September 18, 2025Option 2nd is correct
Vmax is 60 but km cannot be determined.
anjani sharma
September 19, 2025Answer would be D
As in michealis menten, the graph is plot between Vo and substrate concentration, and here the graph is between the product and time which is not giving any km or V max value.