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The membrane fluidity of murine B16 melanoma and L5178 lymphoma variants is examined in relation to their metastatic potential. A higher lateral mobility of membrane proteins in metastasis is indicated by lectin receptor-mediated agglutination studies, but these do not constitute incontrovertible evidence that higher fluidity might be relevant in the metastatic process. The membranes of tumour cells with higher metastatic potential have a lower cholesterol/phospholipid ratio but greater unsaturated phospholipid content. This is partly supported by partition characteristics of metastatic variants in aqueous two-polymer phases. Steady-state fluorescence polarisation, which measures lipid order and the degree of rotational motion of lipids, does not suggest marked differences in bulk ‘fluidity’ of metastatic variants. Transbilayer fluidity differences have been described and these may be of some significance in the control of activity of membrane-associated enzymes and other membrane properties. The plasma membrane is a mosaic of domains possessing different degrees of microviscosity and this mosaicism may be relevant in the context of metastatic dissemination of tumours.

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The isoelectric characteristics of some nucleic acid preparations from rat liver have been examined. 10S and 4S RNA species and SV-DNA were found to have isoelectric points of 5.2, 6.0-6.7, and 4.35 respectively. The molecular charge ratios (net negative charge/nucleotide) were calculated. Using SV-DNA as a standard, these isoelectric characteristics and charge ratios have been interpreted as indicating that the 10S and 4S RNAs have 35 and 56% of the molecules involved in secondary structure.