Matthew E. Jurek Week 3

Matthew E. Jurek BIOL398-03/S13

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• Final Presentation

The Concentration of Ammonia Regulates Nitrogen Metabolism in Saccharomyces cerevisiae

Eelko G. ter Shure, Herman H.W. Sillje, Arie J. Verkleij, Johannes Boonstra, and C. Theo Verrips

Defining Terms

All definitions from biology-online.org [1]

• Biosynthetic- Relating to or produced by biosynthesis.

• Flux-(Science: radiobiology) The total amount of a quantity passing through a given surface per unit time. Typical quantities include (magnetic) field lines, particles, heat, energy, mass of fluid, etc. Common usage in plasma physics is for flux by itself to mean magnetic field flux, unless specified otherwise.

• Glutamate-(Science: biochemistry, physiology) major fast excitatory neurotransmitter in the mammalian central nervous system.

• Metabolite-(Science: biochemistry) Any substance produced by metabolism or by a metabolic process. Any substance involved in metabolism (either as a product of metabolism or as necessary for metabolism). An end product as a result of metabolism.

• Proline- (Science: amino acid) One of the 20 amino acids directly coded for in proteins. Structure differs from all the others, in that its side chain is bonded to the nitrogen of the amino group, as well as the carbon. This makes the amino group a secondary amine and so proline is described as an imino acid. Has strong influence on secondary structure of proteins and is much more abundant in collagens than in other proteins, occurring especially in the sequence glycine proline hydroxyproline. A proline rich region seems to characterise the binding site of SH3 domains. An amino acid that is found in many proteins (especially collagen).One of 20 amino acids commonly found as part of a protein.

Outline

Introduction

• Ammonia is the preferred nitrogen source of yeast,Saccharomyces cerevisiae, as noted by rapid growth.
• The breakdown, or metabolism, of nitrogen is regulated at two levels: gene expression and enzyme activity.
• Continuous cultures differ in external ammonia concentration and ammonia assimilation.
• It is thought the flux of ammonia is more critical in nitrogen breakdown than ammonia concentration.

Physiological parameters

• A strain of yeast (SU32) was grown under the following conditions in continuous culture in a fermenter:
  • Different ammonia concentrations(mM): 29,44,61,66,78,90,96,114, and 118
  • Fixed glucose concentration (mM): 100
• Such parameters allowed for an investigation of ammonia's influence on both gene expression and regulation.
  • Fig 1A
    • X-axis shows ammonia concentration within the feed
    • Y-axis on the left shows residual ammonia concentration, or ammonia left in culture
    • Y-axis on the right shows biomass/ flux or the product of ammonia metabolism
    • Feed with 61mM ammonia or lower showed ammonia limitation
    • Feed with more than 61 mM ammonia resulted in glucose acting as the limiting factor
  • Fig 1B
    • X-axis shows which feed is used
    • Y-axis on the left shows the oxygen consumed and resulting carbon dioxide produced
    • Y-axis on the right shows the ratio of carbon dioxide produced over oxygen consumed
    • Feed with an ammonia concentration of 44mM or lower resulted in ammonia limitation
    • Input ammonia concentration above 44mM produced a constant respiratory quotient
    • No significant changes in carbon metabolism (aside from 29mM ammonia feed) occurred as excess of ammonia was introduced
• The different steps of glutamine production were observed as ammonia concentrations were increased.
  • Fig 1C
    • X-axis shows the ammonia concentration in the feed
    • Y-axis shows concentration of listed substance based on ammonia
    • Ammonia excess increased the levels of glutamate and glutamine intracellularly