Re: Are more complex enzymes more likely to be denatured by heat?

Afraid I am not sure what you mean by 'convoluted' when talking about an enzyme though the answer to your question is: sometimes yes and sometimes no. There is not a direct relationship between protein quaternary (subunit to subunit) structure and heat stability that acts as a definitive rule. Amino acid sequence encodes conformation (again, usually) and this conformation determines (usually) stability, along with substrates, coenzymes, ligands, etc. Large multisubunit proteins can be more stable then monomeric forms, there is just no cardinal rule. Non-globular proteins do tend to be more heat labile, and often multi-subunit proteins are non-globular, thus with this line of thought larger proteins *are often* less stable then smaller ones. THOUGH THIS IS NOT A RULE, simply an observation from experience. Another factor to consider when looking at thermophillic proteins are molecular chaperones, heat stability usually occurs because of chaperone proteins that actively stabilize the protein at higher temperatures (Hsp-Heat shock proteins are an example), not anything to do with the proteins structure.

Your next question, ability to return to the 'correct' conformation following heat shock. Thermodynamics infer the most stable conformation of a protein is the one it assumes, and this would infer the protein would return to its original conformation following partial denaturation by heat. This is not always the case. Many times chaperones are requried for the protein to obtain its original conformation, proteins can also fold into more then one conformation under stress-such as high heat. Thus, the answer to your question is sometimes yes and sometimes no. Biochemical processes are very complex and not subject to easy guidelines. This dynamic nature is the true beauty of living systems.

Hope this helps!!