Lysosomes

Dan Harper Dan at eidolon.demon.co.uk
Sat Nov 2 06:55:13 EST 1996


>I'm not sure if this is the proper newsgroup, but I am looking for an
>answer to why lysosomes do not "digest" themselves.  Thanks.
>
>> From my reading it seems that 'they' think that
>>the lysosome membrane is not digested by the enzymes because (i) the
>>proteins embedded in the membrane have a tertiary configuration which
>>prevents them being hydrolysed and (ii) the pH that the enxymes are
>>active in is not allowed in the lysosome.

It is not fully understood how the lysosome membrane is impervious to
degradation while it is still functional.  However theories include:

(i) High degree of glycosylation of the lysosomal membrane proteins,
possibly protecting them from the proteases in the lumen.

(ii) Membrane possesses certain proteins that function as enzyme
inhibitors, and unusual lipids that may not be readily attacked by
lipases.

(iii) A protective 'halo' - material interposed between the limiting
membrane and the digestive space, possibly composed of domains protuding
from integral glycoproteins and glycolipids of the lysosomal membrane.

Note:   The lysosomal enzymes are optimal at c. pH 4.8, this is the pH
of the lysosome, if the pH were different the lysosome would not be able
to perform its degradative functions.  

From:   Dan Harper

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Alt.Contact:    eidolon at bcs.org.uk
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