A simple procedure for the preparation of αs2-casein is presented and the experiments with this fraction and plasminogen suggested that plasminogen activator (PA) activity may be involved in the αs2-casein fraction. For the preparation of αs2-casein, acid-precipitated whole casein treated previously with 2-mercaptoethanol was fractionated in 50% ethanol by the addition of ammonium acetate (50 mM at final concentration) at pH 7.2. The precipitate recovered by centrifugation was fractionated again as above and the resultant precipitate was dissolved in deionized water with NaOH, dialyzed against deionized water and freeze dried. For the determination of proteinase activity, dimethylcasein was incubated with casein fractions at 37℃ for various time intervals in the presence or absence of plasminogen, and the increase in absorbance at 420 nm was measured after the reaction with trinitrobenzensulfonic acid (TNBS). PA activity was estimated by subtracting proteinase activity in the absence of plasminogen (plasmin activity) from that in its presence. PA activity in αs2-casein fraction was also observed by urea-polyacrylamide gel electrophoresis (urea-PAGE). The results of urea-PAGE of this fraction heated at various temperature indicated that the PA activity was relatively heat stable. PA activity in the αs2-casein fraction was 2.5 times higher than that in unfractionated acid casein.
The milk, collected from a ginkgo-toothed beaked whale (Mesoplodon ginkgodens) which was stranded at the beach of Chitou Bay, Baisha village, Penghu County, Taiwan on 30 December, 2002, was analyzed. The milk consists of 66.5% of water, 14.6% of fat, 17.6% of protein, 0.1% of carbohydrate and 1.2% of ash. Fat content is less than that in the Stejneger's beaked whale and those in other whales, whereas protein content is higher. As to minerals, calcium, sodium, potassium, iron, magnesium and zinc were analyzed. Contents of sodium, potassium, magnesium and zinc are higher than those of Stejneger's beaked whale. Among fatty acids composition, oleic acid content was highest and accounted for about 50% of all fatty acids detected. Amino acid composition was similar to that of the minke whale, and glutamic acid and leucine contents were high.