Concanavalin A and wheat germ agglutinin are as effective as insulin in enhancing the rate of glucose transport and in inhibiting epinephrine-stimulated lipolysis in isolated adipocytes. These lectins, also like insulin, inhibit basal as well as epinephrine-stimulated adenylate cyclase activity of membranes obtained from homogenates of fat cells. Low concentrations of wheat germ agglutinin enhance the specific binding of insulin to receptors of fat cells and liver membranes. Higher concentrations of this plant lectin, as well as of concanavalin A, competitively displace the binding of insulin to receptors in these tissues. These effects are equally apparent in insulin-binding proteins solubilized from membranes, indicating that the plant lectins interact directly with insulin receptors. All of the effects observed with the plant lectins are reversed by simple sugars that bind specifically to these plant proteins. Agarose derivatives of the plant lectins effectively adsorb solubilized insulin-binding proteins, and these can be eluted with buffers containing specific simple sugars. The possible implications of these findings to certain biological properties (mitogenicity) of these lectins and to the mechanism of action of other growth-promoting substances are considered.

http://www.pnas.org/content/70/2/485.full.pdf

Insulin-like activity of concanavalin A and wheat germ agglutinin--direct interactions with insulin receptors.

Role of calcium in the hormonal regulation of liver metabolism

Publisher Summary This chapter explains that growth hormone itself exercises no direct metabolic action on skeletal tissue, but rather acts through a second substance, which is detectable both in normal plasma and in plasma from hypophysectomized rats after growth hormone administration. The term sulfation factor is applied to this plasma activity because the assay used for its detection depends upon the in vitro incorporation of radioactive sulfate into proteoglycans of cartilage. The chapter describes with evidence that several distinct growth hormone dependent substances are responsible for the biological activity of plasma in sulfation factor assays and that these substances are all insulin-like; thus, these substances are components of non-suppressible insulin-like activity (NSILA). These insulin-like growth-promoting peptides has much in common with the elusive serum growth factors that are required for the proliferation of cells in tissue culture. The chapter also discusses that the sulfation factor plays a much more pervasive role in somatic growth. The term somatomedin encompasses all growth hormone-dependent plasma factors that mediate the growth of responsive tissues..

The Somatomedins: A Family of Insulinlike Hormones under Growth Hormone Control

INSULIN receptor has been purified by affinity chromatography and studied by affinity labeling techniques. It is composed of two types of subunits, α (molecular weight ∼135,000) and β (molecular weight α90,000), which form a disulfide-linked heterotetramer (αβ)2. Both α- and β-subunits are glycoproteins. Both are exposed on the outer surface of the membrane, a is the subunit that is predominantly affinity labeled by insulin and is probably the insulin-binding subunit; however, β may also comprise a portion of the insulin-binding site. Receptors for insulin-like growth factors have also been affinity labeled. A photoaffinity labeling derivative of basic somatomedin affinity labels a protein with a subunit structure very similar to the insulin receptor. In contrast, multiplication-stimulating activity is affinity cross-linked to a protein with an entirely different subunit structure. After binding to cell surface receptors, insulin, along with its receptor, is internalized by an endocytic process, which in ...

Insulin receptor: structure and function.

Stimulation of a low Km phosphodiesterase from liver by insulin and glucagon.

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1016/0014-5793%2872%2980791-9

K.D. Hepp

Papers

Insulin action on the adenyl cyclase system: Antagonism to activation by lipolytic hormones