Characterization of ferritin from human placenta. Implications for analysis of tissue specificity and microheterogeneity of ferritins.

Mammalian ferritins can be resolved into multiple components by isoelectric focusing, and each tissue contains a characteristic subset of isoferritins. Ferritin isolated from human liver was compared to acidic ferritin isolated from mid-gestational human placenta to define a structural basis for ferritin heterogeneity. Placenta ferritin contained several major bands with isoelectric points in the range of pI = 4.7-5.0 which were more acidic than the predominant isoferritins of human liver. Ferritin from each tissue was resistant to denaturation by 10 M urea and appeared to be identical by electron microscopy. Circular dichroism measurements revealed that placenta ferritin had substantially less ordered secondary structure than liver ferritin. Both types of ferritin contained only two subunits when analyzed by electrophoresis in sodium dodecyl sulfate gels, but isoelectric focusing of dissociated subunits in urea revealed 6-7 different components. In this system, placenta ferritin was enriched in the more acidic subunits and it completely lacked the most basic subunits noted in liver ferritin; placental ferritin had no unique components. Differences in isoelectric points among assembled ferritins from these two tissues appear to result from different proportions of these acidic and basic subunits.

False recognition effects in young and older adults' memory for text passages.

Recent work has demonstrated an age-related increase in susceptibility to illusory memories; specifically, older adults make more false recognition responses to unstudied items when such items are semantically related to studied items. The majority of studies have examined false recognition for semantically associated words; the current study extends that previous work by examining false recognition effects for schematized story actions. In two experiments young and older adults studied schematized stories and were later given a recognition test for studied and unstudied story actions. Our results indicate that both age groups produced robust false recognition effects, but older adults were not more susceptible to these effects. These results suggest there are limits to the range of circumstances that yield age differences in illusory memories.

Age differences in false recognition using a forced choice paradigm.

Recent findings suggest that older adults may be more susceptible to false recognition responses than younger adults because of age differences in gist-based processing at both encoding and retrieval. It has been suggested that age differences in the quality of memory representations that result from this age-related reliance on gist processing can produce age differences in response criteria, with older adults employing more lenient criteria than young adults. Support for this argument comes from studies where suppressed false recognition in older adults occurs with shifts toward more conservative response criteria. The current study further examined this issue by minimizing the effects of response criteria by using a two alternative forced-choice task in the study of false recognition in young and older adults. This manipulation reduced false recognition in both young and older adults, but did not eliminate age differences in false recognition.

Correlations between subunit distribution, microheterogeneity, and iron content of human liver ferritin.

Subunit heterogeneity of human liver ferritin was investigated by two-dimensional electrophoretic methods. The protein which ordinarily remains assembled in 10 M urea solution was dissociated into subunits in acid-urea or sodium dodecyl sulfate solutions. In agreement with earlier studies, the subunits migrated as two bands in sodium dodecyl sulfate or acid-urea gel electrophoresis systems or in two-dimensional combinations of these systems. Isoelectric focusing methods, however, resolved four major subunit bands and three to five minor bands. Each of these components migrated as either a 22 000 or a 19 000 molecular weight component in sodium dodecyl sulfate gel electrophoresis in the second dimension. The multiple subunit model, which is contrary to currently accepted representations of ferritin structure, is compatible with certain inherent properties of the protein. Thus, ferritin was fractionated on the basis of iron content to show that the relative amounts of individual subunit types were directly dependent upon the iron composition of the protein. Iron-loaded molecules were deficient in the most basic subunit types, and apoferritin was enriched in these components. Aspects of microheterogeneity of assembled ferritin molecules were correlated to subunit heterogeneity, and discrete differences in subunit populations among purified isoferritin components were demonstrated.