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Membrane Glycoprotein Differences between Normal Lactating Mammary Tissue and the R3230 AC Mammary Tumor¹

Department of Biochemistry, Oklahoma State University, Stillwater, Oklahoma 74074

Membrane glycoproteins have been studied in the normal lactating mammary gland and R3230 AC mammary tumor of the rat. Plasma membrane-enriched fractions were obtained from these tissues by discontinuous sucrose gradient centrifugation of a microsomal preparation from the tissue homogenates. The lightest membrane fractions (F-1 and F-2) have the greatest enrichment of plasma membrane markers, with a 14- to 20-fold purification of 5'-nucleotidase and Na⁺-K⁺-adenosine triphosphatase over the homogenate values in both tumor and normal tissues for F-1. Electron microscopy shows smooth membrane vesicles for these fractions. Polypeptide analysis by acrylamide gel electrophoresis shows essentially the same patterns for F-1 and F-2 and only relatively minor differences between membrane components of tumor and normal tissues. Glycoprotein analysis of the polyacrylamide gels by periodate-Schiff staining indicates more dramatic differences. Membrane Fraction F-1 from normal tissue contains two major glycoproteins, GP-II and GP-III, while Fractions F-2 and F-3 contain an additional glycoprotein, GP-I, with a higher apparent molecular weight. In the tumor, the component corresponding to GP-III is decreased or absent and a new component GP-IV is seen at a lower apparent molecular weight.

¹ Journal article J-2928 of the Agricultural Experiment Station, Oklahoma State University, Stillwater, Oklahoma. This research was conducted in cooperation with the United States Department of Agriculture, Agricultural Research Service, Southern Region. This research was supported in part by National Cancer Institute Grant NO 1-CB-33910 and by the Oklahoma Agricultural Experiment Station.

² Present address: Department of Biochemistry, University of Kansas Medical Center, Kansas City, Kan. 66103.

Received 11/15/74. Accepted 1/22/75.