Rhizomucor miehei Aspartic Proteinases Having Improved Properties

Abstract

Aspartic proteinases are widely spread in most organisms, where they carry out many different functions. The oldest and most well–known use of aspartic proteinases is as coagulants in cheese–making. The coagulants are probably still the only commercial products containing aspartic proteinases as the active substance. The main commercial interest in coagulants is focused on how to enhance the enzyme activity and its performance during cheese–making. In contrast to this, most commercial interests in other aspartic proteinases deal with how to inhibit their activity in order to control their function. The main commercial coagulants can be divided into three groups according to their origin, animal rennet, fermentation produced chymosin (FPC) and microbial coagulants.¹ Of animal rennets, calf rennet is the traditional and the most desired coagulant for cheese–making, but FPC products made by recombinant organisms and microbial coagulants, the natural aspartic proteinases of the fungi, make up a considerable part of the coagulant market. Fermentation produced chymosin is the product of the future, and the great interest in microbial coagulants is due to the fact that they constitute a significant part of the market because of their lower prices. Rhizomucor miehei aspartic proteinase (EC 3.4.23.23) constitutes the active component of the most widely used microbial coagulant. The molecule consists of 361 amino acids, has a molecular weight of 38701 and contains in addition approx. 6% carbohydrate.² The enzyme is commercially available in its natural form, in various heat labile forms made by post-treatment of the natural form (oxidation) and as recombinant coagulant produced in Aspergillus oryzae.