Chromaffin granule membrane glycoprotein IV is identical with Ac45, a membrane-integral subunit of the granule's H(+)-ATPase.

Glycoprotein IV of bovine adrenal chromaffin granule membranes was purified by membrane fractionation with Triton X-114 and lectin affinity chromatography. An antiserum raised against this protein recognized the same component as one directed against subunit Ac45 of the proton-translocating adenosine triphosphatase in the granule membrane. Amino acid sequencing confirmed that glycoprotein IV and Ac45 are identical proteins, and also showed that they are derived from a larger precursor by removal of a 246-amino acid N-terminal sequence. Enzymatic deglycosylation indicated an apparent polypeptide molecular mass of 29 kDa for the mature Ac45/glycoprotein IV. Blue Native electrophoresis confirmed that this protein is a component of the membrane sector of the V-ATPase.