I have home brewed but never malted my own grain.
Malting is the process of allowing the grain to germinate then roasting the sprouted seed (darkers roasts make darker beer).
It converts starches into simpler carbs that ferment more readely. Not aware of an enzimes needed for brewing being involved. I could be wrong.
The best beers tend to use only barley; American mega-brewers often add other grains (called adjuncts), such as rice and corn (maize). These are used as an inexpensive way to introduce fermentable starches, without adding much body or flavor.
The exception would be specialty beers such as wheat or rye beers. Both of those are nevertheless usually brewed with at least half barley.
When you get right down to it, there are two types of alcohol. Fruit alcohols generally go to make wines (or, when distilled, brandies).
The rest, by and large, are grain alcohols. Scotch, and various other whiskeys are simply distilled grain alcohol.
(Stuff like mead and that fermented mare's milk drunk by mongols are to be counted as exceptions.... One can make alcohol pretty much from anything containing sugar.)
Beer-type drinks can be made from a variey of grains. For example, Japanese sake is made from rice, and there are indeed wheat, millet, rice, and rye beers.
I'm guessing that barley works best.
Finally, beer is distinguished by its use of the hop flower, which acts as a preservative; and by its carbonated nature, which comes from letting yeast operate within sealed containers.
Answer to the enzyme question: In order for grain to germinate and grow it needs enzymes to break down the long starch molecules contained within the husk into simpler sugar molecules. Brewers use the process of malting to more fully develop these naturally occurring enzymes (ALPHA AMYLASE AND BETA AMYLASE) within the grain, and then during the mashing process they heat the grain with water at about 150F (the temperature at which the enzymes work most efficiently) for a half hour or so to complete the conversion from starch to sugar. This "sugar water" is then separated from the spent grains, boiled with hops and then cooled before pitching the yeast for fermentation.
Barley is particularly suited to making beer because it contains higher concentrations of enzymes when malted than wheat, corn, rice or other grains. Also different types of grain (two-row versus 6-row) and different malting procedures (degree of modification) produce different amounts of available enzymes.
From Wikipedia: [Alpha-amylase randomly cleaves the α(1-4)glycosidic linkages of amylose to yield dextrin, maltose or glucose molecules. It adopts a double displacement mechanism with retention of anomeric configuration. Beta-amylase also catalyzes the hydrolysis of a-1,4 glycosidic bonds but only from the non-reducing end to yield maltose molecules. Beta-amylase is present in germinating seeds prior to germination whereas a-amylase and proteases appear once germination has begun.]