Aspartate Aminotransferase

I.U.B.: 2.6.1.1
L-Aspartate: 2-oxoglutarate aminotransferase
Glutamic Oxaloacetic Transaminase

Aspartate aminotransferase (also known as glutamic oxaloacetic transaminase: GOT) catalyzes the following reaction:

Enzymatic reactions involving intermolecular transfer of amino groups are important in metabolic processes; they have been reviewed by Braunstein (1973).

In mammalian tissues the enzyme is especially concentrated in heart and liver tissue. When either organ is damaged there is a marked elevation of serum GOT. This phenomenon is of diagnostic significance and the assay for serum GOT is a very important clinical test.

Aspartate aminotransferase, for which pyridoxal phosphate is a cofactor, exists as two isozymes, one mitochondrial (m-GOT) and the other from the cytosol (s-GOT). Though differing markedly in primary structure, chemical and physical properties, both catalyze the same reaction with subtly different catalytic steps (Stankewicz et al. 1971; Wada et al. 1971; Watanabe and Wada 1971; Marinez-Carrion et al. 1970).

The enzyme most extensively studied is that from pig heart. The usual preparations contain only the cytosol enzyme.

Characteristics of Aspartate Aminotransferase from Pig Heart:

Molecular weight:

m-GOT	91,200 ± 2,700 (Feliss and Martinez-Carrion 1970)
s-GOT	93,000 ± 2,800
s-GOT	94,000 (dimeric) (Polyanovsky et al. 1972)
	47,000 (monomeric)

Composition: s-GOT comprises four subunits separable by ion-exchange chromatography or electrophoresis (Martinez-Carrion et al. 1967). Denisova and Polyanovsky (1973) report on the different activities and sugar and sialic acid moieties in the four subforms. See Braunstein (1973, page 393). See also Ovchinnikov et al. (1973).

Extinction coefficient: = 14.0 (Polyanovsky et al. 1972).

Optimum pH: 8.0.

Activators: Pyridoxal or pyridoxamine phosphate activate undenatured enzyme (Jenkins et al. 1959). See also Walter et al. (1975).

Specificity: Aspartate aminotransferase acts upon a number of aromatic amino acids (See table in Shrawder and Martinez-Carron 1972). See Braunstein (1973, page 435.)

Inhibitors: p-mercuribenzoate (Stankewicz et al. 1971), L-α-methylaspartic acid (Melander 1975), 2-amino-3-butenoic acid (Rando 1974), maleate, succinate, glutarate and adipate (Jenkins et al. 1959).

Stability: In solution the enzyme may be stabilized with α-ketoglutarate and EDTA in maleate or succinate buffers. (Jenkins et al. 1959).

Worthington lyophilized preparation is stable 6 - 12 months at 5°C.