The major human and murine histocompatibility antigens are tetrameric molecules with an apparent molecular weight of about 130,000. They are composed of two types of polypeptide chains. The two light chains, previously identified as 6B2-microglobulins, are bound to the two heavy, alloantigenic HL-A or H-2 polypeptide chains by noncovalent interactions only. The heavy chains are held together by disulfide bridge(s) located in the part of the molecule that is attached to the cell membrane.By limited proteolysis of the histocompatibility antigens evidence was obtained suggesting that the heavy chain may consist of three compact domains connected by more extended stretches of polypeptide chain. Each domain appeared to contain a single disulfide bridge encompassing about 60 to 70 amino-acid residues.Staphylococcus aureus protein A is known to bind exclusively to the Fc region of immunoglobulin G. It was, however, observed that protein A interacts in a similar way with the H-2 antigen heavy chain. This observation, together with the homology of the primary structure of ,62-microglobulin to immunoglobulin G, the tetrameric structure of the alloantigens, the organization of the heavy polypeptide chain into compact domains, and the presence of a single, immunoglobulin-like disulfide loop in each domain, establishes a close similarity in structure between histocompatibility antigens and immunoglobulins. The similarity in structural features suggests a common evolutionary origin of the two types of molecules.

The partial amino acid sequence of the epidermal growth-factor-binding protein was determined. Residues in 108 unique positions, corresponding to 45 % of the molecule, were identified. The protein is a serine protease, closely related to the nerve growth factor 7 subunit. It is suggested that the epidermal growth-factor-binding protein, like other serine protease, is synthesized as a single polypeptide chain which undergoes limited endoproteolysis.The isolated material also contained minor amounts of a second serine protease. This protease is closely related to the epidermal growth-factor-binding protein, differing from it in 7 out of the 45 amino acid positions available for comparison. The latter protease may be identical to the previously described protease A.

Many different cleaning agents were used. The average exposure to solvents was low, but some working tasks included relatively high short-term exposure. To prevent adverse health effects, it is important to inform workers about the health risks and to restrict the use of the most toxic chemicals. Furthermore, it is important to develop good working procedures and to encourage the use of personal protection equipment.

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