Succinylated asi-casein

Primary Mode of Reaction and Consequences (9). Bovine a8i-casein (Variant B) was prepared from fresh milk (12) and immediately succinylated to increase water dispersibility (13). This succinylated asi-casein preparation, molecular weight of ca. 25,000 daltons, was used as the hydrophilic protein substrate. The compound L-norleucine 1-13C-dodecyl ester, prepared from K13CN and 1-bromoundecane through four steps (14,15,16), was used as the lipophilic nucleophile. C-13 NMR measurements showed that this sample gave only one signal at a distance of 65.2 ppm from the signal of tetramethylsilane (TMS). 

Another experiment was carried out with the 5-min, 15-min, and 30-min incubation mixtures in order to determine the correlation between their content of the 20,000-dalton product and the emulsifying activity. The result was that the emulsifying activity increased in accordance with the formation of this polypeptide (see Table II). No increase in the emulsifying activity results when succinylated asi-casein is incubated with papain in the absence of L-norleucine n-dodecyl ester. 

All of the data from Table II indicate that, under the unconventional conditions intentionally set in the present study, papain can catalyze the aminolysis of the ES intermediate that probably occurs from succinylated asi-casein (substrate) and papain (enzyme) by L-norleucine n-dodecyl ester (nucleophile), with formation of a surface-active 20,000-dalton product to which this lipophilic nucleophile is attached covalently as illustrated in Figure 1. The observed amphiphilic function of the 20,000-dalton product is probably a result of the formation of a localized hydro-... 

Table I. Properties of a 20,000-Dalton Polypeptide Formed from Succinylated asi-Casein by Treatment with Papain in the Presence of L-Norleucine l-13C-Dodecyl Ester...

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