Specific absorption studies upon calf rennin.

Abstract

The question of the identity of pepsin and rennin has been under consideration for many years, Pekelharing, 1 Pawlow 2 and others, holding to the view that pepsin and rennin activities were not distinct, with Hammarsten, 3 and more recently Fenger, 4 claim that the two activities are different in character.

The study made in this laboratory was carried on in order to help bring further proof as to the identity of these two activities.

A very active preparation of rennin was made by the method of Fenger. 4 The dried product from this method of preparation showed on the average a milk-curdling power of 1:1,000,000 in ten minutes on fresh pasteurized milk at 40° C. Reprecipitation of this material gave a final product 41.66 times as active as Armour's commercial rennin. It was more active than could be consistently prepared by the sodium chloride salting out process and it had the advantage of being free from absorbed sodium chloride. The product can be kept for a long time without losing activity.

Studies were then carried out in order to determine if a more active product could be prepared. This was attempted by absorbing the rennin activity from the calf preparation, on solid purified casein suspended in solutions at various pH values. In these studies it was observed that the rennin activity could be absorbed to the extent of 90 to 95 per cent when the pH value of the solution was from 4.4 to 4.6. This was shown to be true by testing the filtrates, after absorption, for milk curdling power. It was also observed that the absorbed rennin activity could be recovered from the casein to the extent of 75 per cent to 80 per cent by bringing the solution to a pH value of from 6.4 to 6.6 by means of NaHCO₃.