Developmental changes in brain-specific enolase isoenzymes.

to membranes in brain and liver was similar to, but more marked than, that observed with Mg2.+ (Table 2). This can be explained on the basis of a possible interaction between cations and the negatively charged groups on the endoplasmic-reticulum membranes. Brain endoplasmic reticulum has considerably more phospholipid than liver, hence the requirement for spermine and Mg2+ may also be greater in brain than in liver. Alternatively, structural differences between the ribosomes from liver and brain might be responsible for the differential requirement of cations in the ribosomemembrane interactions in brain cortex and liver. The possible functional significance of the observed structural differences between the endoplasmic reticulum of secretory and non-secretory tissues requires investigation.