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THE CONTRIBUTIONS OF DIFFERENTIAL CENTRIFUGATION TO THE INTRACELLULAR LOCALIZATION OF ENZYMES

1957; SAGE Publishing; Volume: 5; Issue: 6 Linguagem: Inglês

10.1177/5.6.552

1551-5044

Alex B. Novikoff, Estelle Podber,

Nuclear Structure and Function

The most essential contribution of differential centrifugation to our understanding of the cell is so commonplace now that we may overlook it . The intracellular localization of chemical substances, revealed by this technique above all others, implies an inter-dependence of subcellular units. Almost from the birth of cytology, the biologist has assumed such inter-dependence, but it remained for the biochemist to supply the evidence-with cell fractions obtained by differential centrifugation. In Figure 1 we have diagrammed one of the most striking instances of biochemical inter-relatedness of subcellular units in the liver cell, the only cell with which we shall deal. We have drawn both the biochemical and structural aspects in extreme form, for purposes of discussion. The two most firmly established portions of this diagram come from work of George Hogeboom and Walter Schneider. For almost a decade these two investigators worked together, to spark the rapid advance of this field. Last July, death took George Hogeboom from us. Seven months later, cytochemistry suffered another blow with the death of George Gomori. Both men shall be sorely missed, scientifically and personally. Recent observations of electron microscopy, like the data of differential centrifugation, attest to the complexity and inter-relatedness of subcellular units. Particularly in the hands of Porter and Palade, the electron microscope has revealed a system of membranes within the cytoplasm called by them “endoplasmic reticulum” (68, 66). Increasing evidence is accumulating that in many cells this membranous system is Coiltinuous, at one end with the nuclear membrane (92), and at the other end with the cell or plasma membrane (66, 56). In the liver cell, Watson (92) has estimated that some 10 % of the nuclear surface consists of so-called “pores”, where nucleus and cytoplasm may be in direct continuity. The remainder of the nuclear surface may be conceived, as Palade (66) has done, as a “moat” enclosing the nucleus and connected, through the endoplasmic reticulum, to the cell surface or the material bathing the cell. It was found by Hogeboom and Schneider (34) that the nuclear fraction isolated from sucrose homogenates of liver contained almost all the enzymatic activity leading to the synthesis of diphosphopyridine nucleotide (DPN) from adenosine triphosphate (ATP) and nicotinamide mononucleotide (XMX).