Identification of the N-ethylmaleimide reactive protein of the mitochondrial phosphate transporter

Area of Science:

• Biochemistry
• Mitochondrial Biology
• Protein Chemistry

Background:

• The mitochondrial phosphate carrier is crucial for cellular energy metabolism.
• Sulfhydryl (SH) reagents are known inhibitors of this carrier.
• Previous studies identified potential protein candidates but lacked definitive characterization.

Purpose of the Study:

• To identify the specific protein component of the mitochondrial phosphate carrier.
• To confirm the role of SH-reactive groups in carrier inhibition.
• To characterize the molecular properties of the identified protein.

Main Methods:

• Inhibition of mitochondrial phosphate carrier using SH reagents (p-(hydroxymercuri)benzoate and N-ethylmaleimide).
• Analysis of protein components using dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE).
• Labeling of proteins with N-[3H]ethylmaleimide for identification and quantification.

Main Results:

• A 32,000-dalton protein containing SH groups was identified as a component of the phosphate carrier system.
• This 32,000-dalton protein binds N-[3H]ethylmaleimide, indicating SH group reactivity.
• Other previously proposed proteins (45,000 and 6,500 daltons) were ruled out due to absence or lack of reactivity with SH reagents.
• The mobility of the 32,000-dalton protein on SDS-PAGE was distinct from mitochondrial ATPase gamma subunit and carboxyatractyloside binding protein.

Conclusions:

• The 32,000-dalton protein is identified as a key component of the mitochondrial phosphate carrier.
• The inhibition of the carrier by SH reagents is directly linked to the reactivity of this 32,000-dalton protein.
• This finding clarifies the molecular basis of mitochondrial phosphate transport regulation.