Insulin interactions with purified plasma membranes of rat liver were studied with respect to insulin degradation and specific binding to receptors. W-insulin was rapidly degraded upon exposure to liver membranes. After only 5 min of incubation at 30” of 1251-insulin (0.3 nlvr) and liver membranes (1 to 2 mg of protein per ml), 40 to 60% of the labeled hormone was degraded as measured by its ab...

One of the most unexpected and extraordinary cytological discoveries of electron microscopy was the observation of Sj6strand and Rhodin (9) and Rhodin (8) that the basal cell surface of the proximal tubule of the kidney is extensively and deeply infolded into the cytoplasmic mass. These folds penetrate between mitochondria and form multiple lateral anastomoses. Pease (6, 7) studied other portio...

The three universally accepted mechanisms of chloride transport across plasma membranes are: (i) sodium-coupled symport; (ii) anion-coupled antiport; and (iii) coupling to primary ion transport through electrical and/or chemical mechanisms. No direct evidence has been provided for primary chloride transport despite numerous reports of cellular, anion-stimulated ATPases and of chloride transport...

Using recently developed techniques for solubilization of RNA polymerase from soybean chromatin and isolation of plasma membrane fractions from plants we can show the presence of a transcriptional factor specifically released from the membranes by auxin, 2,4-dichlorophenoxyacetic acid. The nonauxin, 3,5-dichlorophenoxyacetic acid, does not release the factor, but subsequent exposure of the memb...

The sea urchin egg contains one or more tyrosine-specific protein kinase(s) which are active during the response of the egg to sperm fusion. Fertilization results in an 8-fold increase in the relative incorporation of [32P]orthophosphate into phosphotyrosine as compared to phosphoserine and phosphothreonine. Under defined in vitro conditions, plasma membranes from fertilized eggs incorporated 5...

Plasma membranes of a cell contain 2 kinds of Ca2÷-extruding mechanisms to maintain [Ca 2÷] of cytoplasm at submicromolar levels, ATP-dependent and extracellular NaLdependent mechanisms. In plasma membranes of several tissues, the ATP-dependent Ca2+-pumps associate with (Ca 2+ + Mg2÷)-ATPase activity [ 1-3 ]. In the case of erythrocyte plasma membrane, a reconstitution study has clearly demonst...

Plasma membranes of vertebrate lens fiber cells contain a major intrinsic polypeptide with an apparent molecular weight of 26,000 (MIP26). These plasma membranes are extremely rich in communicating junctions, and it has been suggested that MIP26 is a component of them. MIP26 was purified from cow lenses using preparative SDS gel electrophoresis followed by hydroxylapatite column chromatography....

Purified liver plasma membranes were prepared from rats fed a high-fat, carbohydrate-free diet or a high-glucose, fat-free diet. Membranes from rats fed the high-fat diet bound significantly less 125I-labeled concanavalin A (Con A) than did those from rats fed the fat-free diets. The magnitude of the binding difference increased with increasing concentrations of Con A. Neither association nor d...

The widespread assumption that cytoplasts generated from human polymorphonuclear leukocytes (PMNs) are vesicles consisting solely of cytoplasm surrounded by plasma membrane and devoid of granule activity remains to be tested. PMN cytoplasts were prepared by centrifugation of intact cells on a Ficoll step gradient in the presence of cytochalasin B. Two granule membrane markers, Mol, a fluorometr...

Oviductal apical plasma membrane fractions have been successfully used to provide an in vitro model to study the role of direct membrane contact in sperm-oviduct interactions. Apical plasma membrane preparations from pig oviductal tissues show a dose-response in their ability to maintain boar sperm viability in vitro. Membrane preparations obtained from other tissues (lung and duodenum) are inc...