Final answer:
Isocitrate lyase is involved in the glyoxylate cycle, which is utilized by organisms like plants, bacteria, and fungi to convert fats into carbohydrates. This enzyme is not active in animal tissues, as they do not have the glyoxylate cycle.
Step-by-step explanation:
Activities of isocitrate lyase are typically associated with organisms that use the glyoxylate cycle, which is a modified version of the citric acid cycle. The enzyme isocitrate lyase is crucial in the glyoxylate cycle, enabling organisms, like plants, bacteria, and fungi, to convert fats into carbohydrates. This process predominantly occurs in seeds during germination when the carbohydrate reserves are low, and the organism relies on fatty acids for energy. Isocitrate lyase cleaves isocitrate into succinate and glyoxylate, bypassing the two decarboxylation steps of the citric acid cycle where CO2 is released. The glyoxylate cycle is not found in animals, so we don't expect isocitrate lyase activity in animal tissues under normal conditions.