Insulin the simplest unicellular eukaryotes. Apart from animals, insulin-like proteins are also known to exist in the Fungi and Protista kingdoms. Insulin is produced by beta cells of the pancreatic islets in most vertebrates and by the Brockmann body in some teleost fish. Cone snails "Conus geographus" and "Conus tulipa", venomous sea snails that hunt small fish, use modified forms of insulin in their venom cocktails. The insulin toxin, closer in structure to fishes' than to snails' native insulin, slows down the prey fishes by lowering their blood glucose levels. The preproinsulin precursor of insulin is encoded by the "INS" gene.
Pulsatile insulin blood into the liver in variable amounts, closely related to ingestion of meals. For induction and maintenance of insulin-dependent enzymes essential for glucose metabolism in the liver (e.g. hepatic glucokinase, phosphofructokinase, and pyruvate kinase), the hepatocytes require a defined insulin level (200-500 µU/ml in the portal vein) concomitant with high glucose levels (which acts as a bimolecular signal). In non-diabetic subjects, portal insulin concentrations are twofold to threefold greater than those in the peripheral circulation. During the first pass through the liver, 50% of the insulin is removed, strongly insinuating that the liver is the principal metabolic target organ of