NATURALLY-OCCURRING VARIANTS OF HUMAN-MILK BILE SALT-STIMULATED LIPASE

Analysis of milk samples from a number of lactating women revealed mol ecular variants of bile salt-stimulated lipase (BSSL) of both lower an d higher molecular mass than that commonly occurring. In contrast to p revious observations, we report on individuals having only a variant o f lower mass, both one of lower and one of common mass, or both one of lower and one of higher mass of the lipase. From two individuals we p urified the lower molecular mass BSSL variant and characterized it. Th e amount of lipase in the milk of these two individuals was considerab ly less than average (mean of 10 women with BSSL of the most common mo lecular mass). The BSSL variant of lower mass showed the same bile sal t activation, pH dependency, temperature stability as those most commo nly occurring. We could localize the difference in mass to the large O -glycosylated repeat sequence close to the C-terminus of the protein. With respect to all characteristics studied, the BSSL variant of highe r mass was also similar to that most commonly ocurring. Again, the dif ference in mass could be localized to the repeat region of the protein . Hence, it appears as if the repeat region, normally carrying 16 repe ats of 11 amino acids each, varies in size between individuals. (C) 19 97 Academic Press.