lecture6 - 10.492 - Integrated Chemical Engineering (ICE)...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
Lecture #6 – Whole Cell Biocatalysts: Enzyme Production (The Growth Phase); By-Product Formation, Substrate/Product Inhibition and Toxicity (The Conversion Phase) Handout : Whole Cell Conversion Case Studies Recall that one of the things that makes a whole cell process different from a purified enzyme process is that in the former case, we now have two phases of process design: the growth phase and the conversion phase. We’ll consider each of these phases in turn, but remember that in all cases, the “active” ingredient is an enzyme and the characteristics of enzymes that we’ve studied to date will still apply. 1. The Growth Phase Enzyme Production The growth phase is in many ways the most critical part of a whole cell bioconversion process because it’s during this phase that the enzyme in which we’re interested will be produced. In the “ideal” scenario, the enzyme will be produced throughout all phases of the growth cycle and its production will not depend on the presence of any other compound in the growth medium. In the most common scenario, this is far from the truth! We will not be able to go into all of the details of how one would design or optimize a growth medium to maximize production of the enzyme of interest (a large but critical task). Instead, we will focus on a few specific ways to optimize enzyme production, including: pH and temperature optimization, inducible gene expression (positive control), and overcoming catabolite repression (a form of negative regulation of gene expression). A. Optimizing pH and Temperature In considering pH and temperature, this is conceptually straightforward. Typically speaking, microorganisms will grow optimally at the temperature and pH of their naturally-occurring habitat. We assume that evolution is pretty efficient and that the bugs will have been optimized for home growth! A bacterium like E. coli , which is naturally found in the human gut, will grow at body temperature (37 °C) and roughly neutral pH (usu. 7.2-7.5). On the other hand, many yeast tend to thrive at lower temperatures (30-35 °C) and acidic pH (~4-5). While generally speaking, the physical conditions that favor optimal growth of the organism will also favor production of the desired enzyme, this is not always the case. Therefore, although a whole cell process requires that you optimize both growth and conversion phases, you cannot do one independently of the other Experimentally, this is accomplished by testing the growth of the organism under a variety of conditions, and then observing how well the resulting cells perform the conversion. NOTE THAT THE GROWTH CONDITIONS CAN AFFECT NOT JUST 10.492 - Integrated Chemical Engineering (ICE) Topics: Biocatalysis MIT Chemical Engineering Department Instructor: Professor Kristala Prather Fall 2004 Dr. Kristala L. Jones Prather, Copyright 2004. MIT Department of Chemical Engineering
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
THE CONVERSION (IE, THE SPECIFIC ACTIVITY OF THE CATALYST) BUT ALSO THE EE!!! As an example, consider this reaction from Problem Set #2, Problem
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 6

lecture6 - 10.492 - Integrated Chemical Engineering (ICE)...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online