Seasonal Evolution of Hydrophilic and Hydrophobic Peptide Contents in Cheeses Made from Ewe’s Goat’s or Cow’s Milk

Proteolysis is the principal and most complex biochemical event occurring during the maturation of the majority of ripened cheese varieties. In addition to softening the cheese body, proteolysis influences the development of cheese flavour via the formation of amino acid and peptides which make a direct contribution to flavour. Goat, cow and sheep cheeses have been elaborated with raw milk and calf rennet. The extent of proteolysis was monitored over six months of ripening and means of HPLC peptide profile analysis. The influence of season on the changes in hydrophobic and hydrophilic peptides and the HO/HI ratio during the ripening of the cheeses were studied.

Ligation of VLA-4 on T cells stimulates tyrosine phosphorylation of a 105-kD protein.

The VLA/integrins are a family of heterodimeric adhesion receptors shown to be involved in cell-to-cell and cell-to-extracellular matrix (ECM) interactions. Given recent evidence that VLA molecules can synergize with the CD3/T cell receptor (TCR) pathway to activate T cells, it is important to identify biochemical event(s) generated by these molecules. Here, we report that the engagement of VLA-4 on T cells with specific antibodies or its ligand activates protein-tyrosine kinase (PTK) activity as detected by antiphosphotyrosine immunoblotting. The crosslinking of VLA-beta 1 (CD29) with a specific monoclonal antibody (mAb) (anti-4B4) plus anti-mouse immunoglobulin resulted in the rapid tyrosine phosphorylation of a 105-kD protein (pp105) in the human T cell line H9, as well as in peripheral resting T cells. The increase in tyrosine phosphorylation of pp105 was specifically mediated by VLA-4, since mAbs against alpha 4, but not against other VLA alpha chains, could induce this phosphorylation. In addition, the binding of T cells with the CS1 alternatively spliced segment of fibronectin (the binding site recognized by VLA-4) induced pp105 tyrosine phosphorylation. Crosslinking the CD3 complex or VLA-4 molecules with mAbs demonstrated that each of these molecules stimulated the tyrosine phosphorylation of unique sets of proteins with different kinetics, suggesting that these two receptor systems are coupled to distinct PTKs. Since tyrosine phosphorylation of cellular proteins has been shown to be a crucial biochemical event in cell growth, our findings suggest that the induction of pp105 tyrosine phosphorylation via VLA-4 may play a role in the transduction of activation signals through this molecule.

A scheme for the partial fractionation of cheese peptides

Although proteolysis is regarded as the most important biochemical event in the ripening of most cheese varieties (Rank et al. 1985; Grappin et al. 1985; Law, 1987), current methods for the fractionation of cheese N, yield very heterogeneous fractions (Rank el al. 1985; Grappin et al. 1985; Fox, 1989). This communication describes the results to date of a study undertaken to develop a comprehensive scheme for the fractionation of cheese N.

Regulation of tyrosinase in human melanocytes grown in culture.

Tyrosinase, the enzyme that controls the synthesis of melanin, is a unique product of melanocytes. Normal and malignant human melanocytes grown in culture were used to study the factors that regulate the expression of tyrosinase. Immunoprecipitation experiments showed that newly synthesized tyrosinase appeared as a protein with an apparent molecular weight of 70,000 that was processed to a protein with an apparent molecular weight of 80,000. Neither tunicamycin nor 2-deoxy-D-glucose inhibited this conversion, suggesting that O-glycosylation is the major biochemical event in the posttranslational modification of tyrosinase. Agents that stimulated the proliferation of normal melanocytes also stimulated tyrosinase activity. Melanocytes with low levels of tyrosinase activity synthesized less tyrosinase, processed the enzyme more slowly, and degraded it more rapidly than melanocytes with high levels of tyrosinase activity. We conclude that tyrosinase activity in cultures of human melanocytes derived from different donors is determined predominantly by its abundance.

The Relevance of Blood Tests in the Management of Thromboembolism

Fibrinopeptide A (FPA) levels reflect fibrin I formed by thrombin proteolysis of fibrinogen - a single biochemical event in fibrin formation and thrombosis. Studies in symptomatic patients suspected of venous thromboembolism (TE) demonstrated a good correlation in 40/45 patients between elevated FPA levels and the presence of thrombosis and/or pulmonary embolism indicated by venogram and/or lung scan and in 50/55 patients between normal FPA levels and the absence of TE. Within 15 minutes of intravenous heparin in 30 patients with documented TE, FPA levels had reached the normal range. In 3 of 17 patients studied over 10 days of anticoagulant therapy elevated FPA levels were associated with recurrence or extension of embolism. Thus, plasma FPA measurements may be useful in the diagnosis and management of venous TE. A second biochemical event - fragment X formation by plasmin cleavage of the Aα and N-terminal Bऔ chains of fibrinogen - can be monitored as thrombinincreasable fibrinopeptide B immunoreactivity. Initial studies suggest imbalance between thrombin and plasmin action favoring thrombin during the inception of thrombosis and favoring plasmin during resolution. The use of these tests is providing specific and quantitative information concerning biochemical reactions associated with clinical TE. In correlation with 125I-fibrinogen scanning and conventional diagnostic techniques, these tests will provide basic pathophysiological understanding which will facilitate the development and use of new techniques in diagnosis, prediction and management of venous TE.

Cytoplasmic DNA and basic protein synthesis in Megalobatrachus davidianus oocytes

Mature Megalobatrachus oocytes contain 43 µg DNA per oocyte, as compared with 250 pg DNA in a hepatocyte of the same animal. Megalobatrachus oocytes respond to CdR treatment by an increased incorporation of [3H]lysine into basic proteins associated with ooplasmic particles, with an optimal CdR concentration at 2 mM. The nucleolus is the most active site of [3H]lysine incorporation. It is suggested that CdR-stimulated basic protein synthesis is a common biochemical event during amphibian oogenesis. The dose response to CdR treatment may be a function of the c-DNA content or c-DNA synthesis potential in the ooplasm.