Studies in protein synthesis with special reference to the pancreas

Douglas, Thomas A (1957) Studies in protein synthesis with special reference to the pancreas. PhD thesis, University of Glasgow.

Abstract

A study has been made of the biochemical changes associated with the formation of secretory granules in pigeon panoreas. This subject was treated as one aspect of the biosynthesis of proteins. Section 1. The composition of the panoreas at rest and during secretion. (1) The effort of different homogenising media on the distribution of Cell constituents in the cell fraction obtained by differential centrifugation was investigated. The two media which were used were 0.25 M sucrose and 0.25 M sucrose buffered at pH 7.2 with 0.2 M Phosphate buffer. The use of the letter medium, which had/higher molarity, led to less efficient sedimentation of particles, with the Result that the cell sap fraction isolated in this medium was enriched Both with total nitrogen and with amylase derived from other fractions. (2) The distribution of amylase and nitrogen was determined in five sub-cellular fractions using 0.25 M sucrose as homegenising medium. The order of occurrence of amylase was as follow :- Cell sap > Microsomes > Mitochondria > Granules > Ultramicrosomes. The distribution of nitrogen was found to be this:- Cell sap > Microsomes >Ultramicrosomes > Mitochondria > Granules. When the concentration of amylase per mg N was calculated it was found that the amylase was more concentrated in the call sap than in the granules. These result indicated that the amylase of the cell sap Could be derived from the rupturing of granules during the homegenising process. This interpretation would be valid only if the ruptured granules had a higher amylase content than the granules which were recovered intact in the from of the granular fraction. (3) The examination of the panoreas during the secretary cycle showed that neither the weight nor the total nitrogen content underwent any significant change. The amylase content underwent a reduction of about 50% during depletion. Two hours later, however, the amylase content had risen to level above that found in the resting panereas. The cellular sub-fraction which underwent the greatest change in amylase content during depletion was the cell sap (- 54%); the microsomes and mitochondria changed by - 30% under the same conditions. During the recovery phase of the secretary cycle, the most marked gain in amylase content was to be found in the cell sap. Compared with the other cell fraction, the microsomes lost the largest percentage of their initial protein content during depletion. on the other hand, the concentation of amylase per mg N in the microsome fraction was found to be constant during the secretary cycle. This suggested that the microsome fraction was losing particles of a fixed amylase-to-protein ratio. Section 2. The uptake of 14C-2-glycine by the proteins of different cell fractions of the pancreas. (1) Measurement was made of the uptake of 14c-2-glycine into proteins of pancreatic cell sub-fractions. In the first instance, sucrose-P04 was the homogenising medium, The result obtained led to the conclusion that the cellular sub-fractions obtained with this medium were not homogeneous. (2) On repetition of the 14C uptake experiments using 0.25 M sucrose as homogenising medium we found that, at short time intervals, the microsome fraction had the greatest uptake. At all time intervals the uptake into the ultramicrosomes was less than that into the microsomes. (5) The pattern of incorporation of 14C-2-glycine in pancreases of birds Injected with carbamyleholine was very arrived and no definite conclusion could be arrived at as to any change in incorporation as a result of depletion, Section 3. The metabolism of RNA during the secratory eyele in the pancreas. (1) The quantitutive change in RNA during the secretary cycle was investigated. It was found that there was no appealable change in RNA content per gm. Of pancreas as compared to controls. (2) Using 32P as a precursor, no definitely increased incorporation Into nucleotides of RNA of the pancreas was obtained during the secretory eyele. The labelling of nucleotides required the use of very large doses of isotope (500/ c 52P per bird). (3) Using 14C-2-glyelne as a precursor of the purines of pancreatic RNA no significant increase in incorporation could be detected after stimulation with cerbamylebeline. This confirmed the quantative and the 32P data. (Abstract shortened by ProQuest.).

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Additional Information: Adviser: J N Davidson
• Keywords: Biochemistry
• Date of Award: 1957
• Depositing User: Enlighten Team
• Unique ID: glathesis:1957-72560
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 11 Jun 2019 11:06
• Last Modified: 11 Jun 2019 11:06
• URI: https://theses.gla.ac.uk/id/eprint/72560