A high level of heparin, infused into blood, often causes severe complications such as hemorrhage, especially when a drug is administered over a long period. The most common way of preventing a patient from bleeding after transfusion is by administering a heparin antagonist such as protamine. The complex molecules formed between heparin and protamine, if left in the bloodstream, may cause hypotension and other side effects. Protamine was immobilized as a bioligand on the affinity matrix formed by grafting an acrylic polymer on cellulose backbone. By flowing blood tangentially along the matrix surface immobilized with protamine, 70-90% heparin reduction was achieved from 1 L of blood containing 10 IU/ml of heparin studied in vitro. The acrylic gel surface avoids lysis of blood, the cellulose support sustains the flow of viscous blood at 50 ml/min, and the tangential flow design permits direct processing of blood without pressure buildup in the system. The example demonstrates the feasibility of applying such a device as a means of immunoadsorptive filter for the selective removal of disease-causing factors from blood.

1. The replacement of the phenolic proton of tyrosine by alkyl, aryl or acyl groups completely abolishes the chymotryptic hydrolysis of tyrosine esters. Similarly, chymotrypsin fails to hydrolyze the tyrosyl bonds of dinitrophenyladrenocorticotropin.2. Several model substrates have been synthesized and characterized. The action of chymotrypsin was followed potentiometrically in buffer containing some alcohol. The hydrolysis of the analogous compounds unsubstituted a t the phenolic group was normal.3. We conclude that inhibition is due, not to an inductive effect, but to a blocking effect which is markedly affected by replacement of the phenolic proton, even with a group as small as a methyl group.In the course of our effort to develop an isotopic chemical method for the assay of adrenocorticotropin by dinitrophenylation with fluor~dinitro-[~H]-benzene and subsequent hydrolysis with chymotrypsin, it has been observed that no bis(dinitropheny1)-seryltyrosine could be identified from the digested mixture. We inferred that the o-dinitrophenyl derivative of tyrosine may interfere with the action of chymotrypsin of tyrosyl peptide bonds [l]. The rates of hydrolysis of the ester bond of L-tyrosine derivatives having the general formula I with R' = H are somewhat increased or decreased depending upon the nature of the substituents on the amino group [2], but very limited work has been done on the esterase activity of chymotrypsin when the phenolic group of tyrosine is blocked by alkylation [3] or acylation. I n order to verify our hypothesis, model substrates of structure I were synthesized, and the esterase action of chymotrypsin on them was studied.

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