Re: Could SpongeBob really live in a pineapple under the sea?

Dear Molly,

Pineapple contains a powerful protease (as does papaya) and this rapidly digests the gelanin (= collagen fibres) in jelly. The enzyme is unusual, in that it is almost unaffected by pH, unlike most enzymes. This suggests that the active site is determined by disuphide bridges, rather than the (more normal) hydrogen bonds.

I once made a starter for a summer lunch party, which consisted of mayonnaise, chicken, grapes, peanuts and pineapple, served as a cold dish in the empty half-pineapple shells. I made it an hour or so beforehand and when the guests arrived, the mayonnasise had separated because the albumin in the egg had been digested! It looked AWFUL! Clearly the enzyme is VERY powerful!

Hence its use in 'Hawaiian-style' meat dishes, where FRESH pineapple can be used to break down the tough fibres in the meat. More usually, canned pineapple is used, where it just tastes good!

Another example was in WW II, when a group of Australian survivors from a plane or shipwreck, found themselves on a part of the Indonesian peninsula which had water and tropical fruit - particularly pineapples and papayas. They had pleanty to live on, until they were rescued. When they were picked up some 3 months later, their teeth had all fallen out, due to the enzymes digesting the suspensory fibres in their jaw!

Seawater is a solution of (mainly) sodium chloride at about 3.5% concentration. As such, it has powerful osmotic and disinfectant properties, and saltwater is a good, cheap treatment for sore throats! The sodium and chloride ions bind powerfully to charged groups in membrane and other proteins, and denature them. They would therefore be expected to do the same to the pineapple enzymes, thus rendering them ineffective.

More importantly, the vast volumes of water in the oceans would dilute the enzyme and so minimise its effects. It would, however, work well at the sort of pH and temperatures found in the sea.

The pineapple would also float, being less dense than seawater and would rapidly decay too! Not an ideal (mobile?) home!

This could form the basis of a project - mix small cubes of hard-boiled egg-white (or jello) with (fresh) pineapple juice, mixed 50:50 with fresh water. Time how quickly they break down on a warm day. Then repeat with seawater, instead of freshwater - and don't forget the controls - BOILED pineapple juice and seawater alone!

The science behind the movie thus seems a bit dodgey (no surprise there!)

BUT

The question I cannot answer is, what use is this very powerful enzyme to the pineapple itself? Perhaps answering that can be YOUR future route to a Nobel prize!

Moderator's note: Zoology Moderator Allison Gong adds the following:

Sponges can live just about anywhere there's water to be filtered. Some can live in pretty foul water, while other species prefer clean water. I'm inclined to think that if you took a pineapple, cut it in half, and sunk it, sponges would be among the "fouling" organisms to colonize it. Unless, of course, the bromelain enzyme does indeed dissolve all of the spongin. Even so, if the pineapple is colonized by other animals first, say, mussels or tunicates, sponges could certainly grow on the secondary surfaces they provide.

Now, the shoes and those disturbing tidy-whities are another story! :-)