Lab Report Sample: Effect of Temperature on Catalase Activity

Model Answer

Abstract

This report investigates the effect of temperature on the rate of activity of catalase, an enzyme that catalyses the breakdown of hydrogen peroxide (H₂O₂) into water and oxygen. Fresh potato tissue was homogenised to provide a consistent catalase source, and the volume of oxygen gas released from a 20-volume H₂O₂ solution was recorded over 60 seconds at six temperatures between 10°C and 60°C. Reaction rate increased steadily from 10°C to a peak of 22.0 cm³ O₂ min⁻¹ at 40°C, then fell sharply to 1.3 cm³ O₂ min⁻¹ at 60°C. These results are consistent with a rising rate of molecular collision up to an optimum temperature, followed by progressive denaturation of the enzyme’s tertiary structure at higher temperatures. A Q₁₀ value of approximately 2.0 was calculated for the 20–30°C interval, in line with typical enzyme-catalysed reactions.

Introduction

Enzymes are globular proteins that act as biological catalysts, lowering the activation energy of specific reactions by providing an alternative reaction pathway (Berg, Tymoczko and Stryer, 2015). Catalase is found in almost all aerobically respiring cells and protects tissue from oxidative damage by rapidly converting the toxic by-product hydrogen peroxide into water and oxygen: 2H₂O₂ → 2H₂O + O₂. Because oxygen gas is released as the reaction proceeds, the rate of this reaction can be measured directly by collecting the volume of gas produced in a fixed time, making catalase a convenient and widely used model enzyme for investigating factors that affect reaction rate at undergraduate level (Reece et al., 2017).

Like all enzyme-catalysed reactions, catalase activity is temperature-dependent. As temperature rises, the kinetic energy of both enzyme and substrate molecules increases, raising the frequency and energy of successful collisions and therefore the reaction rate, broadly in line with collision theory (Campbell and Farrell, 2014). However, enzymes are proteins whose activity depends on a precise three-dimensional shape held together largely by hydrogen bonds and hydrophobic interactions. Beyond an optimum temperature, this structure begins to break down – a process called denaturation – and the active site can no longer bind substrate effectively, causing activity to fall away sharply (Nelson and Cox, 2017). The combination of these two competing effects – a rate-enhancing rise in molecular kinetic energy and a rate-reducing loss of enzyme structure – typically produces a bell-shaped curve of activity against temperature, with a relatively narrow optimum rather than a simple continuous increase (Daniel, Danson and Eisenthal, 2001).

Catalase is of particular practical interest because hydrogen peroxide is both a normal by-product of aerobic metabolism, generated for example during beta-oxidation of fatty acids in peroxisomes, and a widely used antiseptic and bleaching agent, so understanding how quickly it is broken down has applications ranging from cell biology to industrial biotechnology, where catalase is used to remove residual peroxide from textiles and food packaging (Chaplin and Bucke, 2013; Robinson, 2015). Measuring the rate of oxygen release therefore provides a simple, low-cost practical method for exploring general principles of enzyme kinetics that apply well beyond this single reaction. The aim of this investigation was to determine the temperature–rate relationship for potato catalase across a range of 10–60°C, to identify the approximate optimum temperature for this enzyme under the conditions used, and to quantify the associated measurement uncertainty using the Q₁₀ temperature coefficient.

Method

Apparatus: fresh potato tuber, pestle and mortar, distilled water, filter funnel and gauze, 20-volume hydrogen peroxide solution, 10 cm³ syringes, boiling tubes, water baths set at 10°C, 20°C, 30°C, 40°C, 50°C and 60°C, thermometer, gas syringe (100 cm³), delivery tubing, bungs, stopclock, and an electronic balance (±0.01 g).

Procedure: 20 g of peeled potato was homogenised with 40 cm³ of distilled water using a pestle and mortar and filtered through gauze to produce a standardised catalase extract. For each temperature, 5 cm³ of extract and 5 cm³ of 20-volume H₂O₂ were placed in separate boiling tubes and equilibrated in the corresponding water bath for five minutes to allow both solutions to reach the target temperature. The two solutions were then combined in a boiling tube fitted with a bung and delivery tube connected to a gas syringe, the stopclock was started immediately, and the volume of gas collected after 60 seconds was recorded. Each temperature was repeated three times using freshly prepared extract, and the boiling tube was rinsed with distilled water between repeats to avoid contamination. Extract concentration, substrate concentration and reaction volume were kept constant throughout so that temperature was the only variable deliberately changed.

Controlled variables: the same batch of potato extract was used across all repeats at a given temperature, prepared fresh at the start of each session to minimise loss of activity through standing; the H₂O₂ concentration (20-volume) and volume (5 cm³) were identical for every trial; and the same gas syringe was used throughout to avoid systematic differences in friction or calibration between apparatus. A risk assessment was completed before the practical: hydrogen peroxide at 20-volume is an irritant, so gloves and eye protection were worn, spills were rinsed immediately with water, and the higher-temperature water baths were handled with tongs to avoid scalds.

Results

Table 1 shows the volume of oxygen gas collected after 60 seconds for three repeats at each of the six temperatures tested, together with the mean and the range used as an estimate of uncertainty.

Table 1. Volume of O₂ produced in 60 seconds by potato catalase at six temperatures (n = 3 per temperature).

Because gas was collected over exactly 60 seconds, the mean volume in cm³ is numerically equal to the mean rate in cm³ O₂ min⁻¹. Rate increased from 2.3 cm³ min⁻¹ at 10°C to a clear maximum of 22.0 cm³ min⁻¹ at 40°C, before falling to 1.3 cm³ min⁻¹ at 60°C. This pattern is plotted in Figure 1.

Figure 1. Mean rate of oxygen production against temperature.

Worked calculations. The temperature coefficient Q₁₀ describes how much the rate increases for a 10°C rise and was calculated for the 20–30°C interval, where the enzyme was not yet denaturing:

Q₁₀ = Rate at 30°C ÷ Rate at 20°C = 12.3 ÷ 6.3 = 1.95 ≈ 2.0

The uncertainty in the gas syringe reading was taken as ±0.5 cm³. Expressed as a percentage of the mean reading, this uncertainty was largest at the lowest rate and smallest at the highest rate:

At 10°C: (0.5 ÷ 2.3) × 100 = 21.7%    At 40°C: (0.5 ÷ 22.0) × 100 = 2.3%

This shows that the readings at the lowest temperatures, where less gas was produced, carry proportionally the greatest measurement uncertainty, and this is reflected in the wider range bars for those repeats in Table 1.

Discussion

The results support the hypothesis that catalase activity increases with temperature up to an optimum, then declines rapidly as the enzyme denatures. Between 10°C and 40°C, rising temperature increased the kinetic energy of enzyme and substrate molecules, raising the frequency of effective collisions at the active site and producing an approximately exponential increase in rate, consistent with a Q₁₀ close to 2 (Berg, Tymoczko and Stryer, 2015). The sharp fall in rate above 40°C is best explained by progressive denaturation: heat energy disrupts the hydrogen bonds and hydrophobic interactions that maintain the enzyme’s tertiary structure, distorting the active site so that hydrogen peroxide can no longer bind efficiently (Nelson and Cox, 2017). By 60°C, activity had fallen to only 6% of the peak rate recorded at 40°C, suggesting that most of the enzyme population was irreversibly denatured at this temperature.

The optimum of around 40°C recorded here is slightly higher than the 35–40°C range most commonly cited for plant catalases in undergraduate texts (Reece et al., 2017), which may reflect the five-minute equilibration period used, differences between potato cultivars, or a genuine optimum close to the upper end of the typical range. It is also possible that the true optimum lay between the 40°C and 50°C data points and was not captured precisely by the 10°C intervals used; a smaller interval of 2–5°C around the suspected optimum would allow it to be located more accurately in a repeat investigation.

Several limitations should be considered when interpreting these results. First, enzyme concentration was standardised by volume of homogenate rather than by a measured protein concentration, so variation in potato tuber composition between repeats could have introduced some error; two potatoes of different ages or storage conditions could plausibly contain different catalase concentrations even at identical homogenate volumes. Second, the five-minute equilibration period, while sufficient for the small reaction volumes used, may not have allowed the potato extract to reach the water bath temperature exactly at the moment the reaction was started, particularly at the higher temperatures where thermal gradients within the tube are greater. Third, gas loss through the bung seal, if present even briefly, would cause the recorded volume to underestimate the true reaction rate; this was minimised by checking each seal before starting the stopclock but was not measured directly. Finally, using a fixed 60-second collection window meant that at higher rates the gas syringe approached its 100 cm³ capacity, which could slightly compress the true rate at 40°C if the plunger encountered resistance near the top of its range.

The small range values in Table 1 (0.5–1.0 cm³ across repeats) suggest that the practical method itself was reasonably precise and repeatable at each individual temperature, and that the overall shape of the curve in Figure 1 is likely to reflect a genuine biological pattern rather than random measurement scatter. This is supported by the fact that the rate roughly doubled between each of the 10°C, 20°C and 30°C readings, closely matching the calculated Q₁₀ of 2.0, before the pattern broke down abruptly once denaturation became the dominant effect above 40°C. Nonetheless, with only three repeats per temperature and a single potato as the tissue source, the sample size was too small to calculate a meaningful standard deviation or to generalise confidently beyond this specific batch of extract; a class-pooled data set combining results from several groups using different potatoes would give a more robust estimate of the true optimum and its variability.

Future work could address these limitations by measuring enzyme activity with a colorimetric or spectrophotometric assay to quantify protein concentration directly, by extending the equilibration period and monitoring extract temperature with a data logger, and by using a smaller temperature interval around 35–45°C to pinpoint the true optimum more precisely. Repeating the investigation with a second tissue source, such as celery or liver, would also help establish whether the optimum temperature found here is specific to potato catalase or reflects a more general property of the enzyme.

Conclusion

This investigation found that the rate of oxygen production by potato catalase increased with temperature between 10°C and 40°C, reaching a maximum mean rate of 22.0 cm³ O₂ min⁻¹ at 40°C, before falling sharply to 1.3 cm³ O₂ min⁻¹ at 60°C. A Q₁₀ of approximately 2.0 was calculated for the pre-optimum range, consistent with typical enzyme kinetics, and the decline above 40°C is attributed to progressive thermal denaturation of the enzyme’s active site. These findings are broadly consistent with the published literature on plant catalases and demonstrate, using a simple gas-collection method, how temperature governs the balance between increased molecular collision and structural stability that determines enzyme activity.

References

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