Microtubule-associated adenylate cyclase.

Area of Science:

• Biochemistry
• Cell Biology
• Neuroscience

Background:

• Microtubules are key cytoskeletal components involved in various cellular processes.
• Adenylate cyclase is a crucial enzyme in signal transduction pathways, regulating cyclic AMP (cAMP) levels.
• Previous research has explored the association of enzymes with cytoskeletal elements.

Purpose of the Study:

• To investigate the presence and characteristics of adenylate cyclase activity associated with purified microtubule proteins from bovine and rat brains.
• To determine the regulatory properties of this microtubule-associated adenylate cyclase, including its response to known activators and inhibitors.

Main Methods:

• Purification of microtubule proteins from bovine and rat brains through repeated cycles.
• Assay of adenylate cyclase activity using filtered microtubule preparations.
• Testing the effects of forskolin, fluoride, guanine nucleotides, hormones, Ca2+/calmodulin, and divalent cations (Mg2+, Mn2+) on enzyme activity.
• Evaluating the effect of adenosine P-site agonists on cyclase activity.

Main Results:

• Twice-cycled microtubule protein preparations exhibited adenylate cyclase activity that passed 0.2-micron filters.
• The activity showed significant activation by forskolin (2-7 fold) and modest stimulation by fluoride, particularly with added Al3+.
• The enzyme was largely insensitive to guanine nucleotides, hormones, and Ca2+/calmodulin.
• Adenylate cyclase activity was observed with both Mg2+ and Mn2+, with higher activity in the presence of Mn2+.
• Enzyme activity was inhibited by agonists of the adenosine P site.

Conclusions:

• Microtubule-associated adenylate cyclase activity is present in both bovine and rat brain preparations.
• This enzyme exhibits unique regulatory properties, distinct from typical membrane-bound adenylate cyclases, particularly its insensitivity to guanine nucleotides.
• The findings suggest that the catalytic unit of adenylate cyclase, and potentially the Ns regulatory protein, may cycle with microtubules, implying a novel role in cellular signaling or microtubule dynamics.