METABOLISM OF HISTONES IN MALIGNANT TISSUES AND LIVER OF THE RAT AND MOUSE

The ninth Frederick H. Verhoeff lecture. The life history of retinal cells

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Studies on histones and non-histone proteins from rats treated with dimethylnitrosamine

A study has been made of the histone and non-histone chromosomal proteins of rat liver after treatment in vivo with dimethylnitrosamine (DMN) (2 mg/kg). DMN was found not to affect histone turnover, as measured by 3H-labelled amino-acids incorporation. A decrease was observed in specific activity of the histones with time after injection of [14C]DMN or [14C]-formate and this was attributable to demethylation of both abnormal and normal methylation sites in these proteins. In the case of the non-histone proteins, DMN was found to increase greatly the turnover of those non-histone proteins loosely associated with chromatin DNA and RNA; turnover of those non-histone proteins tightly bound to chromatin DNA and RNA was unaffected. Demethylation of both normal and abnormal methylation sites was found to take place from both non-histone protein fractions. In the case of the loosely bound non-histone proteins a lower rate of demethylation was observed after DMN treatment.

Treatment of immature mice with gonadotrophins. Effects on some enzymic activities of unfractionated ovarian homogenates

Treatment of immature mice with both follicle-stimulating hormone and human chorionic gonadotrophin in vivo resulted in large increases in the specific activities of ovarian alkaline phosphatase and alkaline nucleotidase. The specific activities of other ovarian enzymes studied were not altered by gonadotrophin treatment. A simultaneous change in the Michaelis constant of ovarian alkaline phosphatase accompanied the increase in specific activity. These changes commenced 6-8h after injection of human chorionic gonadotrophin plus follicle-stimulating hormone. Injection of human chorionic gonadotrophin induced the change in Michaelis constant and increased ovarian alkaline phosphatase activity. Treatment with follicle-stimulating hormone had no effect on ovarian alkaline phosphatase. However, follicle-stimulating hormone synergistically augmented the response to human chorionic gonadotrophin. A latent period of about 24h elapsed before this augmentation was expressed. Augmentation of ovarian alkaline phosphatase was directly related to the dose of follicle-stimulating hormone at a fixed dose of chorionic gonadotrophin. No response of ovarian alkaline phosphatase was observed after treatment of immature mice in vivo with oestrogens, progesterone, growth hormone or prolactin. Unlike chorionic gonadotrophin, sheep luteinizing hormone over a wide dose range induced no response within 24h. However, a response in ovarian alkaline phosphatase was observed when sheep luteinizing hormone was administered in combination with follicle-stimulating hormone. The specific activity and K(m) of ovarian alkaline phosphatase increased during normal maturation. The Michaelis constant ceased to increase as sexual maturity was reached. The changes in alkaline phosphatase activity were of a similar magnitude to those induced by gonadotrophin treatment. It is concluded that the changes induced acutely by treatment in vivo with unphysiological doses of gonadotrophins occur in the maturing mouse under the influence of endogenous, homologous gonadotrophins at physiological concentrations.

Immunochemical investigation of the modal specificity of taste

The taste mechanism was investigated in a primate (Macaca mulatta). Based on the hypothesis that intracellular enzymes contribute to the transduction of tastes to electric impulses by taste cells, a histochemical survey of the activity of several enzymes was made on taste buds from regions of the mouth associated with sweet, salt, sour, and bitter tastes. Considerable differences were noted among the modalities, which confirmed the hypothesis. An exclusively bitter enzyme was identified.

The histones of some human tissues

1. Histones were examined from five human tissues, namely thymus, liver, placenta, bronchial tumour and peripheral leucocytes. 2. The four main histone fractions [F1, F2(b), F2(a), and F3] were isolated and characterized. 3. The amino acid analyses, N-terminal group analyses and electrophoretic patterns were very similar to those of the corresponding fractions of calf thymus. 4. The yields of fractions F1 and F2(b) were high in human thymus, in human bronchial tumour and in some preparations of normal human leucocytes. 5. It is concluded that the pattern of nuclear histones found in lower forms of life was conserved during the evolutionary process leading to man.

Histones of genetically active and inactive chromatin

It has frequently been proposed that a variation in the relative content of lysine-rich, moderately lysine-rich, and arginine-rich histones might provide a mechanism by which specific portions of the genome may be genetically regulated. This possibility was investigated by comparing the electrophoretic pattern of these three fractions in cells differing markedly in their content of genetically active and genetically inactive chromatin. Three models were used: heterochromatin versus euchromatin; metaphase cells versus interphase cells, and mature lymphocytes versus phytohemagglutinin-stimulated lymphocytes. In no case was there a significant difference in the histone patterns of these contrasting models. It is concluded that, although histones may act as a generalized repressor and structural component of chromatin, factors other than a variation in histone pattern may be responsible for repression or derepression of specific segments of the genome.

The electrophoresis of histones in polyacrylamide gel and their quantitative determination

1. A new method has been devised for the separation of the histone fractions of calf thymus by electrophoresis in polyacrylamide gel at pH2.4. 2. The fractions have been characterized by their relative mobilities with respect to a marker protein, bovine plasma albumin. 3. A method has been developed for the quantitative determination of the separated histone fractions by measuring the colour yields of dye-histone complexes formed in the gel.

Trout-liver histones

1. The histones of trout liver were examined and four main fractions (f1, f2b, f2a and f3) were isolated and characterized. 2. The amino acid analyses, N-terminal group analyses and starch-gel electrophoresis patterns are remarkably similar to the corresponding fractions of calf thymus. 3. The group f2a was also separated into two subfractions, f2al and f2a2, which are similar to those of calf thymus.

Metabolic properties of histones from rat liver and thymus gland

1. The incorporation of (14)C-labelled amino acids into acid-extractable proteins from rat-liver and -thymus nuclei confirmed the existence of a protein component with a higher uptake than that into the major histone components. 2. This rapidly labelled component appeared to contain the thiol groups detectable in the acid extracts. 3. Histone f1 contained 1mol. of serine phosphate/mol. of mol.wt. of 42000-43000. 4. Phosphate was present in other components of the 50mm-hydrochloric acid extract from liver and thymus nuclei, and was probably associated with the thiol-containing component. 5. The difference in amino acid uptake into the histones of diffuse and dense chromatin was confirmed. Dense chromatin was found to have a higher proportion of disulphide than did diffuse chromatin.