Abstract: Separation of tPA and undesired proteins is securely and effectivity accomplished by using a cation-exchanger in the two step procedure for selective elution of undesired proteins from the cation-exchanger on which tPA and undesired proteins are adsorbed: undesired proteins having the pI equivalent to or lower than that of tPA was eluted out in the first step and then undesired proteins having the pI equivalent to or higher than were eluted in the second step.

Abstract: Crude tPA containing, as an impurity, a protein which is reactive with an anti-human tPA antibody and has a molecular weight of 110,000.+-.20,000 daltons is purified by bringing the crude tPA into close contact with an affinity reagent containing an immobilized Kunitz inhibitor which is produced in seeds of Erythrina latissima and other Erythrina plants and acts as an inhibitor on trypsin, plasmin and tPA but does not act on urokinase, so that tPA is collected selectively.

Abstract: Tissue plasminogen activator (tPA) species having a molecular weight of about 70,000 daltons is isolated in a purified form from a crude tPA preparation containing various tPA species having different molecular weights by bringing the crude tPA preparation into contact with a cation exchanger in advance and separating the desired tPA species selectively from the cation exchanger by means of the salt gradient elution method.

Abstract: The distinction of tissue plasminogen activator, especially, the separation of its single-chain species and double-chain species is effected by using the Erythrina trypsin inhibitor which occurs in seeds of a plant of the Erythrina species.

Abstract: A mixture containing a single-chain tissue plasminogen activator (tPA) and/or double-chain tPA is brought into close contact with a column carrying an immobilized Erythrina trypsin inhibitor as an affinity agent. Adsorbed protiens are eluted with eluents having different pHs with or without arginine or benzamidine, so that single-chain tPA is obtained in the eluent with a pH at least 4.5 and double-chain tPA is obtained in the eluent with a pH lower than 4.5.

Abstract: .beta.-Chloroalanine is prepared by reacting in an aqueous medium an aziridine-2-carboxylate with hydrogen chloride in an amount of 2.0-5.0 moles per mole of the aziridine-2-carboxyalte and causing the thus-formed .beta.-chloroalanine to selectively crystallize out from the liquid reaction mixture. Since the solution recovered after the isolation of the crystallized .beta.-chloroalanine still contains .beta.-chloroalanine and by-produced .alpha.-chloro-.beta.-alanine dissolved therein, they may be converted into an aziridine-2-carboxylate by treating them with a base to recirculate it for reuse.

Abstract: DL-cystein is produced by reacting a .beta.-halogenoalanine with a trithiocarbonate to obtain the mono(aminocarboxyethyl) ester of trithiocarbonate and then subjecting the ester to acid decomposition. The above process requires mild reaction conditions, is easy to carry out its reactions and can afford DL-cystein with high yield. It is thus an excellent production process of DL-cystein from the industrial viewpoint.