Studies on thek-casein complex: I. The release of sialic acid-containing material by rennin

Abstract

SummaryWhen k-casein was treated with rennin at neutral pH all the sialic acid contained in the protein was found in the glycopeptide released by the enzyme. From the known molecular weight of the glycopeptide and its proportion in k -casein, a molecular weight of the order of 50000 was calculated for the protein

Studies on the к-casein complex: II. The isolation of a sialic acid-containing fraction by disrupting the complex at low pH in the presence of sodium chloride

“…This is supported by the observation that /c-casein contains sulphydryl groups which are masked. Conditions similar to those employed in freeing /q-casein temporarily unmask the SH-groups although these become unavailable again not through oxidation but presumably because they are once more buried within a tightly formed complex (Beeby, 1964).…”

“…Reaction time, min Waugh et al (1960) reported that /c-casein contained cystine, while Beeby (1964) showed that cysteine and not cystine was present in fresh /c-casein preparations. The lack of cystine or cysteine and the recovery of up to 80 % of the sialic acid of /c-casein in the supernatant after precipitating the protein at pH 3 thus further supports the postulate of Beeby & Nitschmann (1963) that /c-casein is a complex.…”

Milk coagulants

“…A simple but discontinuous method for following the rate of exudation of whey is to measure the volume of whey collected after separation from the curd by a sieve (54). A continuous method, based on the dilution by exuded whey of casein micelles treated so as to be non-coagulable, was described by Beeby (55) and later modified to increase its sensitivity (56). Other methods have been reviewed recently (53).…”

Constitution de la caséine

“…L'hypothèse a été émise que la caséine x est complexe [32,33] ; elle serait formée de 3 unités de même poids moléculaire: 16000, différant entre elles par le contenu en acide sialique et en cystine;…”