Introduction

Abstract

Circulating proteins as discussed in the present study generally will be divided in circulating tissue proteins and plasma proteins. Circulating tissue proteins are present in plasma but have known biological functions outside the circulation. Examples of such proteins are intracellular contractile proteins like myosin or metabolic enzymes excreted into the gastrointestinal tract. The concentrations of these proteins in plasma are usually much lower than in tissues and their presence in plasma is considered as the result of normal leakage of proteins from cells or as a sign of cell death. The large majority of circulating tissue proteins consists of enzymes that catalyse specific intracellular reactions. Therefore they may also be referred to as circulating tissue enzymes.