From owner-metabolic-reg@net.bio.net Mon Feb 24 22:00:00 1997 Path: biosci!daresbury!not-for-mail From: C Cantina Newsgroups: bionet.metabolic-reg Subject: Biochemistry/metabolic regulation question Date: 25 Feb 1997 18:20:27 -0000 Lines: 42 Sender: lpddist@mserv1.dl.ac.uk Distribution: bionet Message-ID: <5evahb$dg1@mserv1.dl.ac.uk> Reply-To: ccantina@iafrica.com MIME-Version: 1.0 Original-To: bioforum@dl.ac.uk, cellbiol@dl.ac.uk, glycosci@dl.ac.uk, microbio@dl.ac.uk, btk-mca@dl.ac.uk Hi, I am a final year BSc student in Biochemistry, Microbiology, and Botany. In the course of enzyme mechanisms I encountered a problem, and do not seem to find the answers in the books I have consulted. Even the lecturer could not answer my question, so I hope that somebody out there might have the answer. (This question goes beyond the scope of the course, so I so not seek an answer to any Test/Exam question, but for my personal gain only!) The enzyme phosphoglucomutase catalyzes the following reversible reaction: Glucose-1-phosphate to Glucose-6-phosphate. This reaction proceeds only in the presence of Magnesium and Glucose-1,6-bisPhosphate; a phosphoryl intermediate is formed in which a phosphate group on a single serine residue of the enzyme is exchanged with substrate and Glucose-1,6-bisPhosphate. 1. Enz-OH + Glucose-1,6-bisPhoshate to Enz-O-Phosphate + Glucose-1(or -6)-Phosphate 2. Enz-O-Phosphate + Glucose-1-Phosphate to Glucose-1,6-bisPhosphate + Enz-OH 3. Enz-OH + Glucose-1,6-bisPhosphate to Glucose-6-Phosphate + Enz-O-Phosphate. Here is the question: Why can the enzyme in the first reaction either cleave the phosphate from position C1 or position C6, but in the last step of the reaction (3.) it only cleaves the phosphate from position C1? Please if any one knows where I can find the answer, or could direct me to it would be greatly appreciated. Please send an email to ccantina@iafrica.com One idea I have is that a sort of steric hinderance could be involved. As said before I cannot find it in the text books. .