The kiln drying of the new malt denatures (destroys) a lot of the different enzymes, but several types remain, including the ones necessary for starch conversion. The amount of enzymatic starch conversion potential that a malt has is referred to as its "diastatic power". .
From a brewer's point of view, there are basically two kinds of malted grain, those that need to be mashed and those that don't. Mashing is the hot water soaking process that provides the right conditions for the enzymes to convert the grain starches into fermentable sugars. The basic light colored malts such as pale ale malt, pilsener malt and malted wheat need to be mashed to convert the starches into fermentable sugars. These malts make up the bulk of the wort's fermentable sugars. Some of these light malts are kilned or roasted at higher temperatures to lend different tastes e.g. Biscuit, Vienna, Munich, Brown. The roasting destroys some of their diastatic power. .
The diastatic power of a particular malt will vary with the type of barley it is made from. There are two basic varieties of barley, two row and six row - referring to the arrangement of the kernels around the shaft. Two row barley is the generally preferred variety, having a bit higher yield per pound, lower protein levels, and claiming a more refined flavor than six row. However, six row has a little higher diastatic power than two row. Historically, the higher protein level of six row barley (which can produce a very heavy bodied beer) drove brewers to thin the wort with unmalted grains like corn and rice. Brewers were able to take advantage of six row barley's higher diastatic power to achieve full conversion of the mash in spite of the non-enzymatic starch sources (adjuncts).
Besides the lighter-colored base and toasted malts, there is another group of malts that don't need to be mashed and these are often referred to as "specialty malts". They are used for flavoring and have no diastatic power whatsoever.