Protein synthesis in a synaptosomal fraction from squid brain.

Area of Science:

• Neuroscience
• Molecular Biology
• Cell Biology

Background:

• Synaptosomes are isolated nerve terminals crucial for studying neuronal function.
• Protein synthesis within nerve terminals is essential for synaptic plasticity and function.
• Previous research has focused on protein synthesis in cell bodies and axons, with less known about nerve endings.

Purpose of the Study:

• To investigate the capacity for protein synthesis in isolated squid brain synaptosomes.
• To characterize the conditions and components influencing synaptosomal protein synthesis.
• To compare the newly synthesized proteins in synaptosomes with those in other neuronal compartments.

Main Methods:

• Incubation of squid brain synaptosomes with [(35)S]methionine to measure protein incorporation.
• Inhibition studies using cycloheximide, chloramphenicol, RNase, and various ionic conditions.
• Sucrose density gradient sedimentation to identify polysomes.
• Gel electrophoresis to analyze the size and pattern of newly synthesized proteins.

Main Results:

• Synaptosomes exhibited significant [(35)S]methionine incorporation into proteins, dependent on time and protein concentration.
• Protein synthesis was inhibited by hypo-osmotic shock, cycloheximide, and modulated by Na(+), K(+), and Ca(2+).
• Newly synthesized proteins, ranging from 14 to 200 kDa, showed distinct electrophoretic patterns compared to axoplasm and cell bodies.

Conclusions:

• Squid brain synaptosomes possess the machinery for active protein synthesis.
• Synaptosomal protein synthesis is regulated by ionic environment and specific inhibitors.
• The distinct protein synthesis profile suggests localized production of proteins within nerve terminals.