title: Specificity of hydrolysis of bovine kappa-casein by cell envelope-associated proteinases from Lactococcus lactis strains.
abstract: The cell envelope-associated proteinases from Lactococcus lactis subsp. cremoris H2 (a PI-type proteinase-producing strain) and SK11 (a PIII-type proteinase-producing strain) both actively hydrolyze the kappa-casein component of bovine milk but with significant differences in the specificity of peptide bond hydrolysis. The peptide bonds Ala-23-Lys-24, Leu-32-Ser-33, Ala-71-Gln-72, Leu-79-Ser-80, Met-95-Ala-96, and Met-106-Ala-107 were cleaved by both proteinase types, although the relative rates of hydrolysis at some of these sites were quite different for the two proteinases. Small histidine-rich peptides were formed as early products of the action of the cell envelope-associated proteinases on kappa-casein, implicating this casein as a possible significant source of histidine, which is essential for starter growth. The major difference between the two proteinase types in their action on kappa-casein was in their ability to cleave bonds near the C-terminal end of the molecule. The bond Asn-160-Thr-161 and, to a lesser extent, the bond Glu-151-Val-152 were very rapidly cleaved by the PIII-type proteinase, whereas hydrolysis of these bonds by the PI-type proteinase was barely detectable (even after 24 h of digestion). Differential hydrolysis of kappa-casein at these sites by the two different proteinase types resulted in the formation of distinctive, high-M(r) products detectable by sodium dodecyl sulfate-polyacrylamide gel electrophoresis.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Chemistry and Biochemistry, Massey University, Palmerston North, New Zealand.
authors.forename: J R
authors.initials: JR
authors.lastname: Reid
authors.forename: T
authors.initials: T
authors.lastname: Coolbear
authors.forename: C J
authors.initials: CJ
authors.lastname: Pillidge
authors.forename: G G
authors.initials: GG
authors.lastname: Pritchard
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000302:isolation & purification / Q000378:metabolism*; D002364:Caseins / Q000302:isolation & purification / Q000378:metabolism*; D002462:Cell Membrane / Q000201:enzymology; D010450:Endopeptidases / Q000302:isolation & purification / Q000378:metabolism*; D006868:Hydrolysis; D013294:Lactococcus lactis / Q000201:enzymology*; D008969:Molecular Sequence Data; D010455:Peptides / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D013045:Species Specificity; D013379:Substrate Specificity
chemical_list: D001426:Bacterial Proteins; D002364:Caseins; D010455:Peptides; D010450:Endopeptidases