Features of enzyme systems in "winter" insects?

there is, of course! The lower threshold of development in most insect species is about +10C. Times these (and some others) if they are active at lower temperatures, then they have special seasonal adaptations. Which ones, I can't say right off the bat. It is necessary to search in the literature... You can start with Ecology of Insect Overwintering.

Right here: http://vivovoco.rsl.ru/VV/JOURNAL/NATURE/02_03/TEMPERAT.HTM

I found the following:

"Amino acid substitutions.
A serious problem for the metabolism of cold - blooded animals at low temperatures is a decrease in the conformational flexibility of proteins, which significantly complicates their functions. Maintaining a certain flexibility of the molecules is achieved by mutations that cause amino acid substitutions in the proteins of animals that live in high latitudes. The nature of such substitutions is studied in detail on the example of the enzyme lactate dehydrogenase. When comparing the amino acid sequences of this protein isolated from the skeletal muscles of Antarctic and South American notothenic fish, it was found that the substitutions are localized in one of the a-helices that form the active center of the enzyme. In most fish of temperate latitudes, a proline residue is located at the beginning of this a-helix, which creates a certain "rigidity" in this area. In Antarctic notothenic fish, proline was replaced with alanine, which provided a more flexible structure for the active site of lactate dehydrogenase, which is so necessary at low temperatures. This is just one of many examples of genotypic adaptations."

The page in general turned out to be interesting, I advise you to look