The Effects of Histones and Other Polycations on Cellular Energetics

A new class of inhibitors for in vitro small intestinal transport of sugars and amino acids in the rat

Polycationic compounds like polylysine, protamine or polyethylenimine may interfere with a cation-related membrane transport system depending on superficially accessible binding sites for particular cations. In vitro experiments were performed using either everted segments of rat small intestine to measure tissue accumulation or everted sacs to determine mucosal-to-serosal transport. The effect of polycations was also tested using brush-border membrane vesicles of rat jejunum. Polycations inhibited the tissue accumulation of methyl alpha-D-glucoside as well as binding of phlorizin. Inhibition of accumulation was increased by raising the polycation concentration and by preincubation of the tissue with the polycations. Kinetic experiments revealed a competitive type of inhibition for the uptake of neutral amino acids and actively transported sugars. Using everted sacs to compare the monomeric cations with their corresponding polymeric forms for their inhibitory effect, it was found that only polymers applied to the mucosal compartment impaired active transport. The passive diffusion of solutes, e.g. 2-deoxy-D-glucose or mannitol, was slightly increased by polycations. With some intermediate oligomers of lysine it could be shown that more than 20 cationic groups are required for approximate complete inhibition. That membrane-related events are responsible for the observed inhibition is suggested by the reduced uptake of D-glucose by brush-border membrane vesicles in the presence of polycations. Therefore an interaction with transport-related cation binding sites, i.e. anionic residues, at the mucosal surface may be assumed.

Histone inhibition of mitochondrial proton transport

Histone blocks proton uptake by mitochondria incubated in the presence of valinomycin or DNP. In the presence of DNP valinomycin-induced H+ uptake is not affected by histone. H+ uptake induced by nigericin is not affected by histone as well. Postulated mechanism of histone action involves the immobilization of proton translocation in mitochondrial membrane and induction of local change in H+ concentration, the prevention of the interaction between H+ and natural K+-carrier and Mg2+ transport system or valinomycin.

Histone-produced magnesium extrusion from mitochondria and magnesium binding to histone

Histone (60 microgram/mg mit. protein) extrudes Mg2+ from mitochondria by 30% with the utilization of endogenous substrates; in the presence of rotenone extrusion drops to about 18%. Dinitrophenol and ADP prevent this effect of histone. Mg2+ extrusion produced by histone depends on histone concentration being at a maximum (100% extrusion) at 107 microgram histone/mit. protein. It was found also that histone alone binds Mg2+ (1.6 nmol Mg2+/microgram histone).

Studies on the action of myelin basic protein (MBP) in rat brain

The specificity of I125-MBP uptake and subcellular distribution on a discontinuous sucrose density gradient, compared to those of histone H 4 and cytochrome c, showed a high affinity of MBP for mitochondria and heavy synaptosomes, and of histone H 4 for lighter synaptosomes. One heavier synaptosomal subpopulation was almost equally labelled by both proteins. Cytochrome c showed only a low uptake into particular material. Receptor interaction studies of MBP with H3-labelled 5-hydroxytryptamine and naloxone gave negative results.

[Possibilities of the regulation of differential DNA activities in higher plants by histone]

By staining calf-thymus histones with fluorescein isothiocyanate and by diazotation it could be shown that externally applied histones enter the cells and accumulate specially in the nucleus. The permeability of the cell membranes does not increase upon application of 100 μg/ml calf-thymus histone (the calf-thymus histone is soluble to less than 50% in water) as measurements of the betacyanin-efflux in tissues of the red beet showed. Application of actinomycin D and calf-thymus histone during the first days of culture (24-72 hrs after culture initiation) inhibits root formation and root growth without diminishing the number of newly formed spots of embryonic cells. Externally applied histone therefore with high probability intervenes mostly in the nucleic acids of the cells.The inhibition of root formation, of differentiation of tracheae and of root growth shows no specific differences upon application of histone from calf-thymus glands or from pea epicotyls or of protamine or poly-1-lysine.With increasing concentration of histone the inhibition of root formation occured over a longer period. After the percentage of free NH2-groups had been diminished by gently acetylation and after the secondary structure had been altered by thermal denaturation of histones, the inhibition of root formation and differentiation of tracheae decreased strongly. The inhibition of root growth, however, still remained. Thermally denatured protamine inhibited root formation and root growth over a longer period than untreated protamine did. The performed acetylation and thermal denaturation hardly lessened the binding capacity of histone to DNA. It is assumed that changes in the histone content of the cells as well as little alterations of histone binding capacity to DNA may play an important role in the regulation of some differential DNA activities by histones and perhaps by other basic proteins.

Effects of basic nuclear proteins on cardiac muscle function

A method for the preparation of semipurified basic proteins from cardiac muscle was presented. At low ionic strengths (below 0.05) and in the presence of Mg ++ , these compounds, as well as purified histones from a variety of tissues, inhibited the Mg ++ - ATP ase activity of cardiac and skeletal muscle actomyosin or myofibrillar suspensions. Under similar conditions, a retardation of superprecipitation occurred. At high ionic strengths (above 0.06) the histones stimulated the Mg ++ - ATP ase.

In the presence of Ca ++ , and at all ionic strengths studied, the histones elicited a marked stimulation of actomyosin ATP ase.

Administration of histones to anesthetized, open-chest guinea pigs, caused a significant depression of the force of contraction of the hearts. These data suggest a possible involvement of basic nuclear proteins in cardiac activity.

Histones and basic polyamino acids stimulate the uptake of albumin by tumor cells in culture

Basic proteins and polyamino acids are taken up by mammalian cells at rates up to 3000 times greater than serum albumin. When given together with serum albumin they increase the albumin uptake by a factor that correlates with their own rate of uptake and can reach more than 50-fold. The lowest threshold of activity detected (10(-10)M)is comparable to the activities of the most potent membrane-active agents.