Globular proteins or spheroproteins are spherical "globe-like" proteins and are one of the common protein types (the others being fibrous, disordered and membrane proteins). Globular proteins are somewhat water-soluble (forming colloids in water), unlike the fibrous or membrane proteins. There are multiple fold classes of globular proteins, since there are many different architectures that can fold into a roughly spherical shape.
Examples:
* Insulin – regulatory hormone for controlling glucose metabolism * Myoglobin – involved in oxygen storage in muscles * Hemoglobin – involved in oxygen transport in blood * Transferrin – involved in iron transport in blood * Immunoglobulins – involved in immune system responses
Fibrous proteins is a protein with an elongated shape. Fibrous proteins provide structural support for cells and tissues. There are special types of helices present in two fibrous proteins α-keratin and collagen. These proteins form long fibers that serve a structural role in the human body. Fibrous proteins are distinguished from globular proteins by their filamentous, elongated form. Also, fibrous proteins have low solubility in water compared with high solubility in water of globular proteins. Most of them play structural roles in animal cells and tissues, holding things together. Fibrous proteins have amino acid sequences that favour a particular kind of secondary structure which, in turn, confer particular mechanical properties on the proteins.
Examples:
* Keratins – found in wool, feathers, hooves, silk, and fingernails * Collagens – found in tendons, bone, and other connective tissue * Elastins – found in blood vessels and ligaments * Myosins – found in muscle tissue * Fibrin – found in blood clots

Enzymes * Enzymes serve a wide variety of functions inside living organisms. They are indispensable for signal transduction and cell regulation, often via kinases and phosphatases. They also generate movement, with myosin hydrolyzing ATP to generate muscle contraction, and also transport cargo around the cell as part of the cytoskeleton. Other ATPases in the cell membrane are ion pumps involved in active transport. Enzymes are also involved in more exotic functions, such as luciferase generating light in fireflies. Viruses can also contain enzymes for infecting cells, such as the HIV integrase and reverse transcriptase, or for viral release from cells, like the influenza virus neuraminidase.

* An important function of enzymes is in the digestive systems of animals. Enzymes such as amylases and proteases break down large molecules (starch or proteins, respectively) into smaller ones, so they can be absorbed by the intestines. Starch molecules, for example, are too large to be absorbed from the intestine, but enzymes hydrolyze the starch chains into smaller molecules such as maltose and eventually glucose, which can then be absorbed. Different enzymes digest different food substances. In ruminants, which have herbivorous diets, microorganisms in the gut produce another enzyme, cellulase, to break down the cellulose cell walls of plant fiber.

Examples: * Catalase - It is a very important enzyme in protecting the cell from oxidative damage by reactive oxygen species (ROS).
Application: sterilization of milk * Glucose Oxidase - Glucose oxidase is synthesized in several species of fungi and insects where it is used to produce hydrogen peroxide which in turn kills bacteria.
Application: removal of glucose from food * Peroxidase – is the plant enzymes that use peroxide to break down bacteria and other harmful material.
Application: paper manufacturing * Cellulase - break down the cellulose molecule into monosaccharides ("simple sugars") such as beta-glucose, or shorter polysaccharides and oligosaccharides.
Application: wine making * Lipoxygenase - is present in oil seeds (particularly soybeans), in cereal grains and in other plant tissues. In the presence of oxygen, the enzyme oxidises unsaturated fatty acids, during which lipid hydroperoxides are produced.
Application: bleach in white bread * Glucoamylase - helps to break down starch that occurs naturally in most vegetables that we eat (in very high amounts in common foods like potatoes, corn, rice, and wheat) or is added as filler or processing additive in many prepared food products. It is a specific type of amylase (starch-digesting enzyme) that our bodies produce in the mouth and pancreas, but it may also be derived from non-animal sources.
Application: starch processing * Amylase – is the digestive enzyme needed to digest carbohydrates.
Application: brewing * Keratinase - have wide range of substrate specificity such as it can degrade other fibrous protein fibrin, elastin, collagen and other non fibrous protein like casein, bovine serum albumin gelatin etc.
Application: leather manufacturing * Funerate Hydratase - is an enzyme that catalyzes the reversible hydration/dehydration of fumarate to malate.
Application: malic acid * Glucose Isomerase - Conversion of glucose to fructose
Application: fructose syrup production

Vitamins * Vitamins are a group of substances that are essential for overall health, normal cell function, growth and development. There are 13 vitamins that are essential for body function. Because these vitamins are so vital to good health, it is important to understand their roles and functions. All essential vitamins can be found in food sources as well as supplemented in various forms.

Examples: * Thiamine (vitamin B1) - Part of an enzyme needed for energy metabolism; important to nerve function. Sources: Found in all nutritious foods in moderate amounts: pork, whole-grain or enriched breads and cereals, legumes, nuts and seeds. * Riboflavin (vitamin B2) - Part of an enzyme needed for energy metabolism; important for normal vision and skin health.
Sources: Milk and milk products; leafy green vegetables; whole-grain, enriched breads and cereals. * Niacin (vitamin B3) - Part of an enzyme needed for energy metabolism; important for nervous system, digestive system, and skin health. Sources: Meat, poultry, fish, whole-grain or enriched breads and cereals, vegetables (especially mushrooms, asparagus, and leafy green vegetables), peanut butter. * Pantothenic acid - Part of an enzyme needed for energy metabolism.
Sources: Widespread in foods * Biotin - Part of an enzyme needed for energy metabolism.
Sources: Widespread in foods; also produced in intestinal tract by bacteria. * Pyridoxine (vitamin B6) - Part of an enzyme needed for protein metabolism; helps make red blood cells.
Sources: Meat, fish, poultry, vegetables, fruits * Folic acid - Part of an enzyme needed for making DNA and new cells, especially red blood cells.
Sources: Leafy green vegetables and legumes, seeds, orange juice, and liver; now added to most refined grains * Cobalamin (vitamin B12) - Part of an enzyme needed for making new cells; important to nerve function.
Sources: Meat, poultry, fish, seafood, eggs, milk and milk products; not found in plant foods * Ascorbic acid (vitamin C) - Antioxidant; part of an enzyme needed for protein metabolism; important for immune system health; aids in iron absorption.
Sources: Found only in fruits and vegetables, especially citrus fruits, vegetables in the cabbage family, cantaloupe, strawberries, peppers, tomatoes, potatoes, lettuce, papayas, mangoes, kiwifruit * Calciferol (vitanim D2) - During childhood and adolescent period Vitamin D is needed for the proper formation of bones and teeth. It also prevents dental caries. Parathyroid gland regulates the calcium level in the blood, and for healthy functioning Vitamin D is essential.
Sources: When sunlight falls upon the surface of the body, a substance present beneath the skin produces Vitamin D. It is present only in meager amounts in butter, eggs and clarified butter. Fish-liver oil is however the best source of Vitamin D.

Lock and Key model of enzymes
To explain the observed specificity of enzymes, in 1894 Emil Fischer proposed that both the enzyme and the substrate possess specific complementary geometric shapes that fit exactly into one another. This is often referred to as "the lock and key" model. This early model explains enzyme specificity, but fails to explain the stabilization of the transition state that enzymes achieve.

Enzyme changes shape by induced fit upon substrate binding to form enzyme-substrate complex. Hexokinase has a large induced fit motion that closes over the substrates adenosine triphosphate and xylose. Binding sites in blue, substrates in black and Mg2+ cofactor in yellow.