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Microsomal membranes were prepared from fresh beans (Phase&s vulgaris) and from samples kept 9 mo at various temperatures and humitidies. Increasing storage severity produced progressively hardto-cook (HTC) beans as well as higher solids loss and lower waterholding capacity during soaking. Membrane phase transition temperature (PTT), calcuated from spin label electron paramagnetic resonance data, also increased and showed a highly significant (r=0.997) correlation with cooked hardness. Fatty acid analysis of membrane lipids demonstrated higher PlT values were due to a significant increase in proportion of saturated fatty acids. These data reflect membrane deterioration during aging that could explain solids loss and water-holding capacity changes. Changes in the membrane may be the primary event in initiation of the HTC defect.

intracellular membranes in that cell type, rather than a property peculiar to the two systems under consideration. Thus any indication of similarity must be viewed critically in the light of studies on other membranes.

SUMMARYA method is described for the preparation of an enriched population of proximal tubules from the cortices of neonate (21-28 d old) rabbits. The method uses collagenase-hyaluronidase digestion, followed by gentle shear to yield a suspension of tubules and glomeruli. Tubular enrichment is achieved by discontinuous density gradient centrifugation in a Percoll gradient. Two fractions were obtained by this method. The denser fraction contained predominantly proximal tubules, was depleted of glomeruli and was enriched in the proximal tubule marker enzyme alkaline phosphatase. Qualitatively similar results to those obtained with neonate animals were obtained with adult tissue. Neonate tubules from the denser gradient fraction grew readily in tissue culture. When examined by electron microscopy the cells exhibited a marked polarity of ultrastructural organization and retained apical tight junctions. Despite this, there was an obvious loss of structure in comparison with in vivo proximal tubule cells. The use of primary culture techniques to study in vitro renal epithelial function is discussed.