Recombinant blood products and therapeutic enzymes - Pharmaceutical Biotechnology: Concepts and Aapplications

Biomedical Engineering Reference

In-Depth Information

CH 2 OH

O

CH 2 OH

O

HO

O

HO

OH

O

OH

Lactase

+

O

OH

H 2 O

OH

HO

OH

Glucose

Galactose

( β-D-Galactopyranose)

Lactose

(

β

-D-glucopyranose

)

(O-

β

-D-galactopyranosyl (1

→

4)

β

-D-glucopyranose)

Figure 12.17 Hydrolysis of lactose by lactase ( β -galactosidase)

Lactose, the major disaccharide present in milk, is composed of a molecule of glucose linked

via a glycosidic bond to a molecule of galactose. The digestive tract of young (suckling) animals

generally produces signifi cant quantities of the enzyme

-galactosidase (lactase), which catalyses

the hydrolysis of lactose, releasing the constituent monosaccharides (Figure 12.17). This is a pre-

requisite to their subsequent absorption.

The digestive tracts of many adult human populations, however, produce little or no lactase,

rendering these individuals lactose intolerant. This is particularly common in Asia, Africa, Latin

America and the Middle East. It severely curtails the ability of these people to drink milk with-

out feeling ill. In the absence of suffi cient endogenous digestive lactase activity, milk lactose is

not absorbed and, thus, serves as a carbon source for intestinal microorganisms. The resultant

production of lactic acid, CO 2 and other gases causes gastrointestinal irritation and diarrhoea. A

number of approaches have been adopted in an effort to circumvent this problem. Most involve the

application of microbial lactase enzymes. In some instances, the enzyme has been immobilized in

a column format, such that passage of milk through the column results in lactose hydrolysis. Free

lactase has also been added to milk immediately prior to its bottling, so that lactose hydrolysis can

slowly occur prior to its eventual consumption (i.e. during transport and storage).

Fungal and other microbial lactase preparations have also been formulated into tablet form,

or sold in powder form. These can be ingested immediately prior to the consumption of milk or

lactose-containing milk products, or can be sprinkled over the food before eating it. Such lactose

preparations are available in supermarkets in many parts of the world.

β