Formation of protein in the pancreas

1. The total known secretory enzyme content of the mouse pancreas has been determined and found to represent about 20 per cent of the weight of the dry, fat-free tissue. 2. The changes in secretory enzyme content that occur during the cycle of secretion and synthesis have been measured. 3. In the course of the cycle no significant changes have been found in DNA or RNA content of pancreatic tissue. 4. Constancy of DNA content, along with other observations, indicates that total protein content of the gland remains substantially unchanged during the cycle of secretion and synthesis. These facts point to the conclusion that following upon the secretion of enzyme protein, synthesis of new protein takes place relatively rapidly in the exocrine cells of the pancreas and this protein is then gradually transformed into the characteristic pancreatic enzyme proteins.     

Active and passive properties of carotid arteries]

A mathematical model of carotid arteries is constructed from the known experimental data. Passive properties of the vascular wall are characterized by an alternating module of elasticity, the active ones by the specific power of muscle contraction. Its maximum value (0,023 n/m-3) is shown to be reached with intravascular pressure 190 mm Hg. The dependence of inner radius on the power of muscle contraction is studied at different values of intravascular pressure. It is shown that theactive properties of carotid arteries are essentially determined by their passive properties and depend on the stretching of the vessel wall.     

Some enzymes of isolated nuclei

THE COMPOSITION OF ISOLATED NUCLEI AND CELL PREPARATIONS FROM TISSUES OF CALF, BEEF, HORSE, AND FOWL WAS STUDIED WITH RESPECT TO THE FOLLOWING COMPONENTS: 1. Liver and kidney arginase, catalase, and uricase; pancreatic lipase and amylase; cardiac muscle myoglobin; erythrocyte hemoglobin; intestinal alkaline phospharase. These are referred to as "special" components in view of their characteristically restricted distribution reflecting the differentiated nature of the tissues in question. 2. Esterase, beta-glucuronidase, alkaline and nucleotide phosphatases, adenosine deaminase, guanase, and nucleoside phosphorylase. These are enzymes of general distribution. The differences in nuclear composition noted with respect to the "special" components, together with the broad variability in nuclear activity found for enzymes of general distribution, led to the conclusion that nuclei are differentiated structures. The following distribution was observed: 1. "Special" components: Hemoglobin was found to be present in fowl and goose erythrocyte nuclei, but myoglobin was entirely absent from heart muscle nuclei; of the special enzymes listed, only catalase and arginase appeared to be concentrated in some of the nuclei. There was no significant nuclear concentration of lipase, amylase, uricase, or alkaline phosphatase. No simple relationship was found between the concentration of a special enzyme in a tissue and its activity in the corresponding nuclei. For example, arginase activity, which is high in mammalian liver and in fowl kidney, was found in liver, not kidney, nuclei. Similarly, catalase activity was demonstrated only in mammalian liver nuclei, although, in mammals, both liver and kidney are rich sources of this enzyme. 2. Enzymes of general distribution fell into three classes: (a) Those present in low concentrations, if at all, in the nuclei-alkaline phosphatase, the nucleotide phosphatases) and beta-glucuronidase. (b) Those present in nuclei in varying concentrations-esterase. (c) Those present in high proportions in most nuclei-adenosine deaminase, nucleoside phosphorylase, and guanase. The exceptionally low nuclear activity of intestinal mucosa with respect to these enzymes was discussed in relation to physiological considerations. The response of nuclei to changes in physiological state was demonstrated by experiments on starvation. The outstanding aspect of this response was a change in nuclear enzymatic activity opposing that observed in the cytoplasm. A comparison of fetal and adult mucosa cells led to the following tentative interpretation of the observed intracellular enzyme distribution: In cells tending to moribundity, as in those subjected to starvation, relative nuclear enzymatic activity falls. The occurrence of special enzymes in nuclei was considered in terms of differentiation, and the high nuclear concentration of the nucleoside-specific enzymes was interpreted in terms of general nuclear metabolic activity.     

The incorporation of N15 glycine by avian erythrocytes and reticulocytes in vitro

A study of the incorporation of glycine-N¹⁵ by chicken red cells in vitro has shown that: 1. There is no detectable nitrogen turnover in the histone or desoxyribonucleic acid of erythrocytes or reticulocytes. 2. Hemoglobin synthesis in the nucleated reticulocyte proceeds at 2 to 3 times the rate observed in the mature erythrocyte. 3. The uptake of glycine-N¹⁵ by heme is 9 to 14 times the corresponding uptake into hemoglobin, and 12 to 20 times the calculated uptake into globin. 4. Maturation of the red cell results in a decline in the rate of synthesis of both heme and globin, but the deceleration is much more marked in globin. synthesis. 5. No significant differences could be detected in the low N¹⁵ incorporations of nuclear and cytoplasmic hemoglobins.     

Methyl green-pyronin; stoichiometry of reaction with nucleic acids

Study of the stoichiometry of the DNA-methyl green reaction by dialysis, precipitation of stain-nucleic acid mixtures, and the staining of nuclei of known DNA content, indicate that the compound consists of one dye molecule per 10 P. The significance of this result was discussed in the preceding paper (1). Histone and lanthanum (and probably other multivalent cations (3)) compete with the dye for the nucleic acid molecule, indicating a common site of attachment, presumably the phosphoric acid groups. With care in the avoidance of procedures which might depolymerize DNA, and the use of a buffer at about pH 4.1, a quantitative histochemical method for DNA by the use of methyl green is possible. Pyronin staining appears to be of qualitative significance only. Slight differences in degree of polymerization, as between the shad and mammalian DNA appear to have no effect on methyl green staining. It may be that a critical level of polymerization for DNA staining exists. This level must exceed 20 nucleotides to account for the 10 P to 1 dye molecule and the effect on the methyl green absorption spectrum; but it may be considerably greater. Beyond this critical level, whatever it may be, further polymerization probably has no influence on staining.     

Histones with high lysine content

1. The preparation and properties of lysine-rich histones, which differ in a number of respects from the classical arginine-rich histones, have been described. 2. Lysine-rich histones, like those previously known, are located in cell nuclei. 3. Lysine-rich histones dissociate more readily from combination with nucleic acid than do other histones.