Home
Resources
Publications
Isoforms of Human Cytochrome-C Oxidase. Subunit Composition and Steady-State Kinetic Properties

Isoforms of Human Cytochrome-C Oxidase. Subunit Composition and Steady-State Kinetic Properties

A B Van Kuilenburg, H L Dekker, C Van den Bogert, P Nieboer, B F Van Gelder, A O Muijsers

Eur J Biochem. 1991 Aug 1;199(3):615-22.

PMID: 1651240

Abstract:

The subunit pattern and the steady-state kinetics of cytochrome-c oxidase from human heart, muscle, kidney and liver were investigated. Polyacrylamide gel electrophoresis of immunopurified cytochrome-c oxidase preparations suggest that isoforms of subunit VIa exist, which show differences in staining intensity and electrophoretic mobility. No differences in subunit pattern were observed between the other nucleus-encoded subunits of the various cytochrome-c oxidase preparations. Tissue homogenates, in which cytochrome-c oxidase was solubilised with laurylmaltoside, were directly used in the assays to study the cytochrome-c oxidase steady-state kinetics. Cytochrome-c oxidase concentrations were determined by immunopurification followed by separation and densitometric analysis of subunit IV. When studied in a medium of low ionic strength, the biphasic kinetics of the steady-state reaction between human ferrocytochrome c and the four human cytochrome-c oxidase preparations revealed large differences for the low-affinity TNmax (maximal turnover number) value, ranging from 77 s-1 for kidney to 273 s-1 for liver cytochrome-c oxidase at pH 7.4, I = 18 mM. It is proposed that the low-affinity kinetic phase reflects an internal electron-transfer step. For the steady-state reaction of human heart cytochrome-c oxidase with human cytochrome c, Km and TNmax values of 9 microM and 114 s-1 were found, respectively, at high ionic strength (I = 200 mM, pH 7.4). Only minor differences were observed in the steady-state activity of the various human cytochrome-c oxidases. The interaction between human cytochrome-c oxidase and human cytochrome-c proved to be highly specific. At high ionic strength, a large decrease in steady-state activity was observed when reduced horse, rat or bovine cytochrome c was used as substrate. Both the steady-state TNmax and Km parameters were strongly affected by the type of cytochrome c used. Our findings emphasize the importance of using human cytochrome c in kinetic assays performed with tissues from patients with a suspected cytochrome-c oxidase deficiency.

Chemicals Related in the Paper:

Catalog Number	Product Name	Structure	CAS Number	Price
IAR4248200	Cytochrome c from human heart			Price

As a specialist in analytical chemical Products, Alfa Chemistry offers consumers a wealth of raw materials and a full range of technologies and services.

QUICK LINKS

HEADQUARTERS

Tel:

Fax:

Email: