DXA (unpublished rosults of J. R.). Thus the origin of tlioso molécules as well as the DNAdépendent DNA polymerase romains an open question. G. S. B. is a visiting professer of the Czeehoslovak Acudomy of Sciences, from Orcgon State Univoraity, sup]iortod by the exchango programme between the Czeehoslovak and tho US Academy of Sciences, and récipient of a cancer devolopmeut award.
Lactoferrin (Lf)t is an 80-kD iron-binding glycoprotein found in high concentrations in human milk and at much lower but detectable levels in a number of other secretions of glandular epithelium (1). The principal functions of Lf are thought to be iron transport and storage (2), and bacteriostasis through strong chelation of iron required for microbial growth (3). However, Lf is also a major constituent of the secondary or specific granules of neutrophils (4), and has been implicated in several operational and regulatory functions in the immune and hematopoietic systems (5). To date, only a single form of Lf has been described, and is presumed to account for all of the diverse functions of the molecule.One of us (M. R. Das) previously reported (6) the presence in human milk of a unique and potent RNase activity, termed human milk RNase (hmRNase). This enzyme was initially identified based on its interference with the detection ofretrovirallike RNAs in human milk, and was subsequently shown to be present in low concentrations in a consanguineous community with a high incidence of breast cancer, the Parsi women of Bombay. The hmRNase was detected in high concentrations only in human milk and was thus considered to be potentially a marker for breast epithelium as well as for risk to development of breast cancer.The hmRNase has recently been purified to homogeneity and revealed to be a high molecular mass (80 kD) glycoprotein with a preference for mRNAs, viral RNAs, and purine homopolymers (7). Activity of the enzyme is influenced by various cations and is optimal at pHs of 7.5-8 .0.We report here that hmRNase is an isoform of Lf, sharing physical, chemical, and antigenic properties with the major species of Lf, but differing from it in the possession of potent nuclease activity and in the lack of significant iron-binding capacity. These findings establish the presence of multiple forms of Lf, with very distinctive properties, that may be related to the highly diverse physiological functions of the molecule .
A unique cell surface antigen of a chemically induced rat hepatoma (Zajdela Ascitic Hepatoma, ZAH) has been identified serologically and purified to apparent homogeneity. ZAH cells, when injected subcutaneously or intradermally into syngeneic hosts, elicit a weak humoral antibody response directed against a single cell surface antigen. In spite of prolonged and extensive immunization, the syngeneic anti-tumor antibodies are solely of the IgM class. Antisera from such immunized animals lyse tumor cells in the presence of complement. These observations were utilized in developing methods for the identification and purification of the antigen. It was observed that administration of purified preparations of this antigen confers ZAH-specific tumor immunity in syngeneic animals. Hence the serologically unique antigen is also the tumor-associated transplantation antigen (TATA) of this tumor. This is the first reported purification of a TATA from a rat tumor. There is considerable earlier evidence for the existence of tumor-associated factors which elicit a strong suppressor-cell response in tumor-bearing rats. The availability of the purified TATA from a rat tumor provides, for the first time, a handle for the identification and further characterization of such molecular species.
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