ISSN:
1573-4943
Keywords:
α-Lactalbumin
;
pepsin
;
trypsin
;
α-chymotrypsin
;
digestion
;
bis-ANS
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
Notes:
Abstract The kinetics of the partial digestion of bovine α-lactalbumin (α-LA) by trypsin, α-chymotrypsin, and pepsin was monitored by lactose synthase activity, HPLC, and difference spectrophotometry. The relative stabilities of the various metal-bound states of α-LA to trypsin and chymotrypsin at 37 and 5°C decrease in the following order: Ca(II)-α-LA〉Zn(II), Ca(II)-α-LA〉apo-α-LA. The HPLC digestion patterns of Ca(II)-α-LA and Zn(II), Ca(II)-α-LA at 5 and 37°C were similar, while the corresponding digestion patterns for apo-α-LA were quite different, reflecting the existence of the thermally induced denaturation states of apo-α-LA within this temperature region. Occupation of the first Zn(II)-binding site in Ca(II)-loaded α-LA slightly alters the HPLC digestion patterns at both temperatures and accelerates the digestion at 37°C due to Zn(II)-induced shift of the thermal transition of α-LA, exposing some portion of thermally denatured protein. The results suggest that the binding of Zn(II) to the first Zn(II)- (or Cu(II))-specific site does not cause any drastic changes in the overall structure of α-LA. The acidic form of α-LA (atpH 2.2 and 37°C) was digested by pepsin at rates similar to that for the apo- or Cu(II), Ca(II)-loaded forms by trypsin or α-chymotrypsin at neutralpH. Complexation of α-LA with bis-ANS affords protection against pepsin cleavage. It is suggested that the protective effects of similar small lipophilic compounds to α-LA may have physiological significance (e.g., for nutritional transport).
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01025092
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