Control of Lactase Activity beyond the Lac-Operon

Controls on β-Galactosidase Activity Beyond Those of the Lac-Operon

As presented to the Virginia Academy of Science, 29 May 2003 Mireille Captieux¹, Taylor Swain², Alicia and Lauren Mills³, Lena Liang⁴, Diana Kuruvilla⁴ and Carl W. Vermeulen, Ph.D.⁵*
(1) University of Edinburgh, Scotland; (2) Jamestown High School, Williamsburg, VA; (3) Messiah College, Pennsylvania; (4) Midwood High School, Brooklyn NY; (5) Science-Projects.Com, Williamsburg, VA (ecoligist@yahoo.com)

Reasoning that there must be more than the genetic level to the story of the control of lactase activity, we sought to reveal the fine controls on enzymatic level. Our work is shown in detail at the link circled in the diagram (left) of the home page of www.science-projects.com. Of particular interest to educators is that all of this work is readily and safely applicable to the teaching lab on the high school level and above. Within the circled link is a set of student lab protocols.

SUMMARY: In vitro, lactase was found to be affected by competitive feedback inhibition. Not unexpectedly, when the molar ratio of galactose to lactose was one, the enzyme was 50% inhibited.

In vivo: On MacConkey agar plates containing a constant concentration of lactose but variable galactose, a lac⁺ gal^- strain of E.coli was phenotypically lac⁺ at low levels of galactose, but became phenotypically lac^- when the molar ratio of gal/lac exceeded one. Interestingly, these lac^- phenotypes contained levels of lactase exceeding those of the wild-type strain. All of this is shown in the following schematic:

What is "Science-Projects.com? Students who access this website are encouraged to work collaboratively on original projects with an aim toward making presentations beyond science fair. This is the seventh presentation made under this logo to societies of professional scientists. The website is owned and operated by Dr. Vermeulen, emeritus microbiologist from the College of William and Mary in Williamsburg, Virginia.