Experiments were conducted to measure the effects of extended freezing on the st

Question

Experiments were conducted to measure the effects of extended freezing on the stability of different metabolic enzymes. Subcellular fractions were freshly isolated and enzyme activities were measured. The microsomes and cytosol were then frozen at -78 degree C for up to two years. Aliquots were thawed and assayed for enzyme activity at different time points. The results (means plusminus standard deviations) are shown below. What can you conclude about the stability of these enzymes when frozen? Overall, what comparison can you make between the stability of microsomal versus cytosolic enzymes? Typically, subcellular fractions that are to be used in repeated experiments are frozen in small aliquots rather than single large batch. Can you suggest a reason for this?

Explanation / Answer

Answer:-

a) The stability of enzymes will be affected not much but literatures are available which suggest there is a drop of around 30% activity with a couple of thaws. According to the given data we can conclude that the activity of cytoslic enzymes are more affected than microsomal ezymes due to freezing, as it is wrapped under microsomal vesicles.

b) It is suggested that we should preserve/freeze the enzyme in small-small aliquots rather than a large batch.

The reason behind it is,after repeatedly thawing of enzyme will destabilize the enzyme and its activity is getting reduced due to sructural distortion. Hence, it is always preffered small aliquots over a large batch.

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