Heparin metachromasia

Metachromasia is of potential value in model systems for pharmacological phenomena because the strengths of the forces involved are probably in the same range as those involved in certain biological molecular processes.The metachromatic properties of heparin have received considerable attention in this context. 

One of the most distinctive properties of these compounds is metachromasia. Certain dyes change color and this change of color is termed metachromasia. Azure A is blue in dilute solution. Addition of heparin or dextran sulfate to this changes it to red-purple. This color change is suppressed by alcohol, heating and by electrolytes. 

Heparins and heparinoids form complexes with proteins and bases, and as shown by the ability to produce metachromasia with submicro quantities are very effective complexing agents in trace amounts. Hence, these substances in trace amounts affect many biological agents such as enzymes, etc. When heparin or a heparinoid is injected in animal or man, an enzyme appears in the blood plasma, lipoprotein lipase. When an oil emulsion is incubated with varying amounts of blood plasma obtained after injection of heparin, the oil is cleared. The heparin has caused the release of this enzyme from tissues to the blood. Heparin and heparinoids have a pronounced action on many enzymes - proteolytic enzymes, carbohydrases, etc. and may inhibit, activate. 

A model [22] of how heparin acts specifically in many biological systems in modifying activities of complex ions may be provided by the metachromatic effect on dyes referred to earlier. The dye. Azure A, shows maximum light absorption at 610 nm. This is decreased when heparin is added, and a new absorption band at 505 mu develops. Heparins and heparinoids are able to produce this color change at very low concentrations and under conditions unfavorable to other metachromatic inducing substances. However, little attention has been paid to the numerous experimental observations reported on metachromasia with heparin and heparinoids, of practical importance to those using this color reaction in studies on heparin and mast cells. In... 

---