Enzymes from mammalian sources generally have an optimum operating temperature near body temperature, and their optimum pH is governed by their location in the body. However, most commercial enzymes are derived from bacterial or fungal cultures that can be grown in large bioreactors to maximize the yield. Research is aimed at isolating enzymes from "extremeophiles", micro-organisms that live in unusual environments and have a tolerance for high temperatures and high or low pH conditions. Enzymes that can operate in "extreme" conditions are regarded as more useful for industrial processes.
Generally you will maximise storage life by keeping enzymes in the fridge. Unless specifically stated, do not store in a freezer. Keep powders dry and make up only enough working solutions for your immediate needs.
The efficacy of enzymes is usually described in terms of their “activity”, or the quantity of substrate they can convert in a given time. This is more meaningful than “concentration” when comparing two similar enzymes. For example, it makes no sense to describe two types of amylase at the same concentration as being equivalent if one is ten times more active than the other.
Enzymes are biologically active proteins that should be handled with care. Proteolytic enzymes in particular may irritate the skin, eyes and mucous membranes. Wear suitable protective clothing such as safety glasses, laboratory coat or apron, and latex gloves. Avoid direct contact or inhalation.