Measurement of fast biochemical reactions

In the 4 years since Hammes (87) reviewed, in this journal, the application of flow and relaxation techniques to the study of primary processes in chemical reactions these methods have been applied to a wide range of biochemical problems. These applications have been facilitated by advances in stopped flow and temperature jump instrumentation, especially with respect to the range of physical properties that may be observed during a reaction, and the availability of instruments.

Progesterone "receptors" in the cytoplasm and nucleus of chick oviduct target tissue

This report demonstrates that the chick oviduct, a specific target organ for progesterone, contains both cytoplasmic and nuclear macromolecules which bind progestins. These binding molecules can be clearly distinguished from transcortin by centrifugation through sucrose gradients of low ionic strength and by agarose gel filtration. The cytoplasmic progesterone-binding molecules also bind 5-alpha-pregnane-3,20-dione, but have significantly lower affinity for cortisol, estrone, or aldosterone. They are absent from blood and nontarget organs such as lung and spleen. The tissue-specific binding components appear to be heat-labile proteins with an average dissociation constant for progesterone of about 8 x 10(-10) M at 2 degrees C. These results are consistent with the identification of the progesterone-binding molecules as the functional hormone receptors. In further support of this concept is the finding that treatment of the chicks with estrogen coordinately induces a 20-fold increase in the number of progesterone-binding molecules and enhances the capacity of progesterone to induce avidin synthesis.A progesterone-"receptor" complex can be detected in both the cytoplasm and nuclei of oviduct tissue after an injection of [(3)H]progesterone to estrogen-treated chicks. By contrast, incubation of oviduct tissue with [(3)H]progesterone in vitro at 2 degrees C for 5 min leads to labeling of the cytoplasmic "receptor" only. Transfer of the "receptor"-steroid complex into the nucleus then appears to occur upon subsequent incubation in vitro at 37 degrees C. This observation suggests that the transfer of bound progesterone across the nuclear membrane may be an energy-requiring enzymatic process.

Macromolecular glucosamine-containing component of the surface of cultivated mouse cells

It has been demonstrated that a glucosamine-containing macromolecular component of the cell surface of 3T3 mouse cells, and SV40-transformed cells, is released from cells by treatment with trypsin under conditions in which the plasma membrane remains functionally intact. This was shown by the fact that the treated cells could be cloned with high plating efficiency and remained impermeable to the vital stain, erythrocin. A method for specifically marking this surface component has been devised based on the finding that in 3T3 cells growing synchronously after subculture by trypsin maximum incorporation of glucosamine into this material occurs 12-13 h thereafter. Of the total radioactive glucosamine incorporated into macro-molecular cell constituents, over 80% was recovered in surface component.

Studies on the biosynthesis of surface component revealed that this was periodic during a cycle of cell duplication, with an increased rate of formation immediately after cell division. It was found that the surface component of 3T3 cells differed from that of SV40-transformed cells.

Cellular metabolism in genetic transformation of pneumococci: requirement for protein synthesis during induction of competence

Metabolic inhibitors have differential effects on various phases of genetic transformation in pneumococci. Evidence is presented suggesting that, in addition to the competence factor, another specific protein or class of proteins is essential for the development of cellular "competence." The precise role of this protein(s) in genetic transformation is not known, but it seems essential for some function subsequent to the interaction of competence factor and cells.

A histochemical study of gut maturation

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The influence of specific chemical factors in the solvent on the absorption of macromolecular substances from the small intestine of the new-born calf

1. The absorption, without change, of [(131)I] and [(125)I]solutes of high molecular weight after duodenal infusion has been measured in anaesthetized calves less than 20 hr old by analysis of lymph collected from the thoracic or intestinal duct.2. Factors present in boiled bovine colostrum whey known to be necessary for the rapid absorption of [(131)I]bovine serum gamma-globulin have now been shown to accelerate the passage of [(131)I]polyvinyl pyrrolidone (PVP) of mean mol. wt. 160,000 (K.60) into the lymph in a comparable manner.3. [(131)I]PVP K.30 (mean mol. wt. 40,000) and [(131)I]human serum albumin could be absorbed to some degree in the absence of solvent factors necessary for the absorption of solutes of higher mol. wt. and a large proportion of the solute thus absorbed passed directly into the portal capillaries.4. Lactate and pyruvate and salts of certain lower volatile fatty acids resemble factors in colostrum whey in their facilitation of the absorption of both gamma-globulin and PVP K.60: these active compounds were not however found in colostrum in significant quantities.5. Potassium isobutyrate was the most effective of the compounds tested and at concentrations of 56.7 m-mole/l. generally accelerated absorption to a greater degree than did colostrum whey itself.6. Absorption of both gamma-globulin and PVP K.60 from colostrum whey was characterized by a profuse flow of lymph containing relatively low concentrations of labelled solute. In contrast, when these solutes were fed in solutions containing simple compounds such as potassium isobutyrate they appeared in very high concentrations in the lymph, the flow of which remained relatively scant.7. When [(125)I]PVP was administered in water, little was absorbed. If, however, such an infusion was followed 3 hr later by a duodenal infusion of colostrum, [(125)I]PVP passed into the lymph almost immediately. This response was too rapid for the colostrum to have reached the absorbing cells in the terminal ileum.8. Intravenous infusions of L+lactate have been found to facilitate the absorption of [(125)I]PVP K.60 introduced into the duodenum in water. This indicates that some of the solvent factors which accelerate absorption may reach the terminal ileum via the blood vascular system after they themselves have been absorbed from the upper small intestine.

The digestive function of lysosomes as studies by the turnover of ingested foreign macromolecules

The persistence of small foreign molecules in lysosomes described by Dr Dingle stands quite in contrast with the fast turnover of foreign macromolecules captured by these organelles. Since Dr de Duve chose to talk today about peroxysomes rather than lysosomes, it might perhaps add to the Discussion to present some data related to this important function, i. e. the ability of lysosomes to digest foreign macromolecular material. As part of our study of the penetration of macro­molecules into mammalian cells (Ryser 1968), we have been studying for some time the fate of 131 I albumin ingested by Sarcoma S180 cells in culture (Ryser 1968; Gabathuler & Ryser 1967). Cells are first labelled with albumin under conditions enhancing albumin penetration (Ryser & Hancock 1965). They are then washed and re-incubated in label-free medium. The fate of the ingested albumin can be followed in two ways; first, by measuring as a function of time the decrease in specific activity of the cellular proteins; secondly, by measuring the radioactivity appearing with time in the re-incubation medium. Figure 60 shows a result of the first type. The value given on the logarithmic ordinate at time zero corresponds to the level of albumin uptake obtained during the labelling period. The loss of acid-insoluble label from the cells is represented by the descending straight lines. This loss is biphasic. Although the second phase has a rather flat slope, it cannot be accounted for by an isotope dilution due to cell growth in vitro . Half-lives of ingested albumin can easily be read from such diagrams, and turn out to be of the order of 50 to 90 min. The rate of breakdown can be influenced to some extent by changing conditions of re-incubation as shown by the difference between the two curves of figure 60, due to a different serum concentration in the medium. Simultaneously with the loss of acid-insoluble activity from the cells, there is a pro­gressive appearance of radioactivity in the re-incubation medium. It was of interest to determine the molecular size of the label appearing in the medium by means of gel filtration on Sephadex G 75. Figure 61 shows the elution diagrams of samples taken from the re-incubation medium at three different times. In all three diagrams there is a strong initial peak of activity excluded by the gel and corres­ponding, therefore, either to unchanged or only slightly modified albumin. It is not yet clear whether this peak results from a desorption of surface-bound albumin or to a regurgitation of ingested material or both. In the upper diagram (sample taken at time zero), radioactivity is found in this initial peak only. As time goes on, however, activity of a different form appears in the medium, as indicated by the occurrence of a second peak, which coincides with the elution of the small-sized marker phenol red (PhR). This peak corresponds to free tyrosin or a dipeptide containing tyrosin. It is evident, therefore, that ingested albumin is broken down not only rapidly, but also thoroughly to the level of free amino acids or dipeptides. Similar evidence has been obtained with phagocytic cells (Mego, Bertini & McQueen 1967; Ehrenreich & Cohn 1968; Unanue & Askonas 1968). Electron microscopy of normal and tumour cells indicates that ingested foreign protein such as ferritin, haemoglobin, peroxydase and 125 I-albumin are essentially localized in secondary lysosomes (multivesicular bodies, phagosomes) (Maunsbach 1966; Neustein & Maunsbach 1966; Friend & Farquhar 1967; J. P. Revel & H. J. -P. Ryser 1967, unpublished data; Ryser, Caulfield & Aub 1962). It can be assumed, therefore, that the intracellular degradation of these proteins takes place in these structures.