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The effect of cycled high pressure treatment of milk on the yield, sensory, and microbiological quality of Cheddar cheese was investigated. Cheddar cheeses were made from pasteurized, raw, or pressure treated milk according to traditional methods. Flavor scores from trained dairy judges were not different for pasteurized and pressurized milk cheeses (P≤0.05). Percent moisture and wet weight yields of pressure treated milk cheeses were higher than pasteurized or raw milk cheeses (P≤0.05). Microbiological quality of pressurized milk cheeses was comparable to pasteurized milk cheeses. Texture defects were present in pressurized milk cheeses and were attributed to excess moisture. High pressure treatment of milk shows promise as an alternative to heat pasteurization prior to cheesemaking.

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Protein L is a multidomain cell-wall protein isolated from Peptostreptococcus magnus. It belongs to a group of proteins that contain repeated domains that are able to bind to Igs without stimulating an immune response, the most characterized of this group being Protein A ( Staphylococcus aureus ) and Protein G ( Streptococcus ). Both of these proteins bind predominantly to the interface of C(H)2-C(H)3 heavy chains, while Protein L binds exclusively to the V(L) domain of the kappa -chain. The function of these proteins in vivo is not clear but it is thought that they enable the bacteria to evade the host's immune system. Two binding sites for kappa -chain on a single Ig-binding domain from Protein L have recently been reported and we give evidence that one site has a 25-55-fold higher affinity for kappa -chain than the second site.

Protein L is a multidomain cell wall bound protein found in ϳ10% of the Peptostreptococcal isolates (1) and contains a series of repeated domains, some of which are able to bind to immunoglobulins without initiating an immune response. Expression of this protein has been correlated to the virulence of these opportunistic pathogenic bacteria (1) that are found in the gastrointestinal and urogenital tracts (2). Its presence has been found to cause cellular responses such as histamine release from basophils and mast cells (3) presumably by crosslinking IgE molecules bound to surface Ig receptors.1 H NMR spectroscopy of a single Ig-binding domain of protein L (isolated from strain 312, PpL 312 ) 1 revealed that PpL 312 is a rigid structure consisting of a ␤-sheet, formed by two pairs of antiparallel ␤-strands, lying on top of a single ␣-helical section (4), with a flexible N terminus (5). Further NMR studies (6) led to the proposal that the binding site of PpL 312 for -chain involves residues from the second ␤-strand and from the loop between the third ␤-strand and the ␣-helix and located the binding site for PpL 312 on the -chain to the second ␤-strand and the two ␤-strands located on the outer surface of the framework region of the V L domain (7).Parallel studies on the binding interaction of a single Igbinding domain of protein L from strain 3316 (PpL 3316 ) found that it forms a high affinity complex with -chains with a K d of 112 nM (8, 9). The x-ray crystallographic structure of this domain has been determined in complex with the human antibody fragment, Fab 2A2, and revealed that two Fab 2A2 fragments can in fact bind to sites on opposite faces of PpL 3316 (10). Site 1 of PpL 3316 is that characterized by Beckingham et al. (9) and equivalent to the site studied on PpL 312 using NMR by Wikström et al. (5). Site 2 of PpL 3316 , involving part of the helix and strands 3 and 4, was identified for the first time by the crystallographic study (10). This site has not yet been characterized although preliminary studies suggested that the affinity of site 2 is lower than that of site 1 (10).By use of a program of site directed mutagenesis we have been able to derive the relative binding affinities of sites 1 and 2 and propose a mechanism by which PpL 3316 binds light chains that is consistent with published data. The hydroxyl group of Tyr 53 is important for the formation of a high affinity complex at site 1. Previous enzyme-linked immunosorbent assay experiments (11) have shown that nitration of Tyr 53 or its mutation to Phe dramatically increases the K d of the -chainPpL 3316 interaction. Another important residue at site 1 is Leu 57 . No binding of the 1 -chain used in these studies can be detected at site 1 of the mutant Y53F/L57H by fluorimetry or isothermal titration calorimetry, and this mutant is thus ideal for measuring the affinity at site 2.Important residues for binding at site 2 are Asp 55 and Ala 66 . The mutation D55A eliminates a salt bridge and dramatically weakens or eliminates binding (12), and co...

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Infertile men with sperm antibodies in serum and seminal plasma undergo premature acrosome loss. This loss may expose the reproductive tract immune system, especially that involving IgA, in autoimmune infertile men and the wives to high immunogenic levels of sperm acrosome membrane antigens, thereby rendering them immunologically infertile.