Enzymes

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Chapter: Pharmaceutical Microbiology : The Wider Contribution Of Microbiology To The Pharmaceutical Sciences

Several enzymes have important therapeutic, medical or pharmaceutical uses. In this article, those enzymes used therapeutically will be described.


ENZYMES

 

Several enzymes have important therapeutic, medical or pharmaceutical uses (Table 26.3). In this article, those enzymes used therapeutically will be described.



 

i)  Streptokinase and streptodornase

 

Mammalian blood will clot spontaneously within minutes if allowed to stand, but if left to stand longer the clot begins to dissolve as a result of the action of a proteolytic enzyme called plasmin. Plasmin is normally present as its inactive precursor, plasminogen. Certain strains of streptococci were found to produce a substance that is capable of activating plasminogen (Figure 26.3), a phenomenon that suggested a potential use in liquefying clots, i.e. fibrinolysis. This substance, called streptokinase, was isolated and determined to be an enzyme.

 


 

Streptokinase is administered by intravenous or intra-arterial infusion in the treatment of thromboembolic disorders, e.g. pulmonary embolism, deep vein thrombosis and arterial occlusions. It is also used in emergency medicine for acute myocardial infarction.

 

A second enzyme, streptodornase, present in streptococcal culture filtrates, was observed to liquefy pus. Streptodornase is a deoxyribonuclease that breaks down deoxyribonucleoprotein and DNA, both constituents of pus, resulting in a reduction in pus viscosity. Streptokinase and streptodornase together have been used to facilitate drainage by liquefying blood clots and/or pus in the chest cavity. The combination can also be applied topically to wounds that have excessive suppuration.

 

Streptokinase and streptodornase are isolated following growth of non-pathogenic streptococcal producer strains in media containing excess glucose. They are obtained as a crude mixture from the culture filtrate and can be prepared relatively free of each other. They are commercially available as either streptokinase injection or as a combination of streptokinase and streptodornase.

 

ii)  L-Asparaginase

 

L-Asparaginase, an enzyme derived from E. coli or Erwinia chrysanthemi, converts l-asparagine to aspartic acid and ammonia. In contrast to normal tissue, some tumours have an essential requirement for l-asparagine and L-asparaginase has therefore been investigated as a selective cancer chemotherapeutic. Although L-asparaginase showed early promise in a variety of experimentally induced tumours, it has primarily found utility in humans for the treatment of acute lymphoblastic leukaemia and occasionally for myeloid leukaemia.

 

iii)  Neuraminidase

 

Many tumours escape immune surveillance through mechanisms including the masking of cell surface antigens by, for example, N-acetylneuraminic (sialic) acid residues. Neuraminidase, derived from Vibrio cholerae, has been used experimentally to increase the immunogenicity of tumour cells by stripping sialic acid residues from the outer surface of certain tumour cells resulting in presentation of tumour-specific antigens to the host immune system. In laboratory animals, administration of neuraminidase-treated tumour cells was found to be effective against a variety of mouse leukaemias. Preliminary investigations in acute myelocytic leukaemia patients have suggested that treatment of tumour cells with neuraminidase in combination with conventional chemotherapy may increase remission rates.

 

iv)                 β-Lactamases

 

β-Lactamase enzymes, whilst presenting a considerable therapeutic challenge due to their ability to confer bacterial resistance by inactivating penicillins and cephalosporins, are nevertheless useful in the sterility testing of certain antibiotics and, prior to culture, in inactivating various β-lactams in blood or urine samples in patients undergoing therapy with these drugs. One other important therapeutic application is in the rescue of patients presenting symptoms of a severe allergic reaction following administration of a β-lactamase-sensitive penicillin. In such cases, a highly purified penicillinase obtained from B. cereus has been administered either intramuscularly or intravenously and in combination with other supportive measures such as adrenaline and antihistamines.

 

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