The hydrolysis of indoxyl esters by esterases of human blood

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Abstract
The rates of hydrolysis of 3 indoxyl esters (and of [alpha]-naphthyl acetate) by the esterases of human red cells and plasma were measured and compared with those of the corresponding phenyl and choline esters. All the substrates are hydrolyzed by both aceto- and butyro-cholinesterase but the non-choline esters are also hydrolyzed by an aliphatic and an aromatic esterase of red cells and an aromatic esterase of plasma. The contribution of the cholinesterases towards the total hydrolysis of the indoxyl esters is far greater than that of the other esterases. The indoxyl and [alpha]-naphthyl esters are hydrolyzed in a similar manner by the esterases, but only slowly, compared with phenyl esters, by the magnesium-sensitive aromatic esterase of plasma. The aromatic esterases of red cells and plasma are not identical. The relative rates of hydrolysis by the 3 esterases of red cells depend upon the substrate concentration employed. It is concluded that the use of either indoxyl esters or [alpha]-naphthyl acetate as substrates in histochemical staining procedures leads to the demonstration of a mixture of esterases.