A number of cytochemical changes were revealed by microscopic observations of Aerobacter aerogenes populations starving for Mg++. During the first few hours, while the synthesis of deoxyribonucleic acid (DNA) was paralleled by an increase in viable bacteria, the cells became progressively smaller. Subsequently, the number of viable cells in the culture remained constant in spite of continuing DNA synthesis, and the cells progressively elongated into filamentous forms. During this time, a second population of very small bacteria could beidentified. These cells, whose number increased progressively, were inert with respect to (i) growth or reproduction when returned to a complete medium and (ii) biosynthetic activity as judged by autoradiographic estimation of uracil-H' incorporation into nucleic acids. When observed by electron microscopy, many thin sections from bacteria that had been starved of Mg+ for 20 hr appeared to be almost devoid of ribosomal particles. Thionine staining indicated that the inert cells contain DNA. Furthermore, the rate of DNA synthesis in the culture corresponded to the rate of accumulation of inert cells, suggesting that their presence-can account for the difference between total DNA and viable count.
The rates of synthesis of Aerobacter aerogenes nucleic acids were estimated during incubation of the bacteria in a Mg++-free medium. Deoxyribonucleic acid (DNA) synthesized during Mg++ starvation, or in the preceding exponential growth, remained acid-precipitable for 2.5 hr before breaking down to acid-soluble products during a period of many hours. Rates of DNA synthesis were calculated by correcting the net amounts of DNA per milliliter to values that would have appeared had there been no decay. After the first few hours, this rate was constant, the amount of DNA present at the start of Mg++ starvation being synthesized every 130 min. Rates of synthesis of total ribonucleic acid (RNA) were established in two ways: (i) by measurements of the incorporation of exogeneous uracil and glucose carbon into RNA, and (ii) by the accumulation of transfer RNA (tRNA), since this component is stable during Mg++ starvation. After the first few hours, this rate was constant, the amount of RNA present at the start of Mg++ starvation being synthesized about every 120 min. Fractionation by gradient centrifugation revealed that at all times of starvation the ratio of newly synthesized tRNA-rRNA was the same as it was during exponential growth. Furthermore, newly synthesized ribosomal RNA (rRNA) became a part of polysomal structures. Thus, in the absence of Mg++, DNA, tRNA, and rRNA were synthesized in the same relative proportions as during exponential growth, at rates close to one-half the instantaneous rates of synthesis in the bacteria growing exponentially at the start of starvation.
Aerobacter aerogenes incubated in a medium containing all factors necessary for exponential growth except Mg++ continued to synthesize nucleic acids and proteins for more than 70 hr, provided the major carbon source was in excess at all times.
Τα αποτελέσματα της χορηγήσεως των αναστολέων της πρωτεϊνικής συνθέσεως, ακτινομυκίνης και πουρομυκίνης, πάνω στην ηλεκτρονικό-μικροσκοπική εμφάνιση των ηπατοκυττάρων νεογέννητων επίμυων, μελετήθηκαν, με ιδιαίτερη έμφαση στις μεταβολές που σχετίζονται με την νεογλυκογένεση και την διάσπαση του γλυκογόνου. Στην εργασία αυτή βρέθηκαν τα ακόλουθα: η χορήγηση της ακτινομυκίνης κατά τη γέννηση οδήγησε σε αναστολή της φυσιολογικής μετά τη γέννηση ανάπτυξης των υπεροξυδοσωμάτων (κυρίως αυτών που δεν είχαν κρυσταλλοειδή πυρήνα), των λυσοσωμάτων και της συσκευής Golgi όπως και σε αναστολή της υδρολυτικής διάσπασης του γλυκογόνου μέσα στα λυσοσώματα. Η χορήγηση της πουρομυκίνης οδήγησε σε αναστολή της ανάπτυξης των λυσοσωμάτων. Αυτά τα αποτελέσματα δείχνουν ότι η ανάπτυξη των δομικών χαρακτήρων των μεταβολικών επεξεργασιών της γλυκογένεσης και της λυσοσωματικής διάσπασης του γλυκογόνου εξαρτώνται από την πρωτεϊνική σύνθεση και ότι τα αγγελιοφόρα RNA γι' αυτή την ανάπτυξη σχηματίζονται μετά τη γέννηση. Η χορήγηση των αναστολέων της πρωτεϊνικής σύνθεσης προκάλεσε διάφορες άλλες μεταβολές όπως ελάττωση του αριθμού και του μήκους των δεξαμενών του κοκκιώδους ενδοπλασματικού δικτύου, ελάττωση της συχνότητας των ριβοσωμάτων πάνω στις μεμβράνες των δεξαμενών, ελάττωση του όγκου του πυρηνίου και μεταβολή του σχήματος των μιτοχονδρίων. Οι μεταβολές αυτές μπορούν να εξηγηθούν με βάση την αναστολή της σύνθεσης του RNA και των πρωτεϊνών. Η πουρομυκίνη επίσης προκάλεσε επιτάχυνση της φυσιολογικής μετά την γέννηση διασπάσεως του γλυκογόνου σαν αποτέλεσμα της γνωστής ενεργοποιήσεως του ενζύμου φωσφορυλάση και αναστολή της ελαττώσεως του αριθμού των ενδομιτοχονδριακών πυκνών κοκκίων σαν αποτέλεσμα πιθανώς της εμπλοκής αυτού του παράγοντα στο μεταβολισμό της αδενίνης και των παραγώγων της.
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