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ANGIOTENSIN CONVERTING ENZYME (ACE)

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General (top of page)

Angiotensin converting enzyme (ACE) is an enzyme catalysing the conversion of Angiotensin I (10 amino acids) to Angiotensin II by removal of a C-terminal His-Leu dipeptide. It is a dipeptidyl carboxypeptidase of MW 140-170,000 which has 2 active sites and requires zinc for activity. The EC number is 3.4.15.1.

ACE is found on all endothelial cells and play a vital role in maintaining blood pressure control as part of the renin-angiotensin-aldosterone system. There is also a testicular form with 1 active site. ACE also has kininase activity, breaking down bradykinin. ACE is produced by monocytes under influence from CD4 lymphocytes, such as may be found as epithelioid cells in granuloma.

Pathology (top of page)

Raised levels of serum ACE are found in the serum of patients with active sarcoid. The serum levels are related to the level of the activity of disease, the amount of granulomata and CXR changes. Serum ACE levels above the normal range are about 75% sensitive for detecting clinically verified sarcoid in the lungs or eyes, however levels are rarely elevated in early sub-acute sarcoidosis. ACE levels fall with remission of disease activity and rise with reactivation, and may be used to monitor treatment.
ACE levels in active sarcoid average 1.5 x the upper limit of normal controls, with levels 3-4 x the upper limit occurring with extensive sarcoidosis involving glandular, hepatic, cutaneous and pulmonary tissues.
Serum ACE may also be raised in other granulomatous conditions such as asbestosis (20% of cases), silicosis (45%), coccidiomycosis and tuberculosis (especially miliary TB, 90%), as well as hyperthyroidism (60%), Gaucher’s disease (80%), alcoholic liver disease (30%) and diabetics (25%). ACE may also be elevated with chronic renal failure.
Serum ACE levels are reduced by treatment with ACE inhibitors or corticosteroids.

Measurement (top of page)

Reference Interval: 40-135 U/L

Sample: Serum (not EDTA). ACE is stable for 20 days at 25°C, or at least 6 months at –20°C.

Assay: Spectrophotometric enzymatic assay using 2-furanacryl-L-phenyl alanylglycine as substrate.

Further Information (top of page)

Review article: Studdy PR, Bird R. Ann Clin Biochem, 1989;26:13-18. Serum angiotensin converting enzyme in sarcoidosis - its value in present clinical practice.

For further information contact Dr Graham Jones, 8382-2179

gjones@stvincents.com.au

Last updated 18/6/99                        disclaimer